PHD2 v2.6.

10
User Guide

June 26, 2021

 Table of Contents
Table of Contents 2
Introduction 4
Main Screen 5
Basic control 5
Menus 6
Status Bar 6
Using PHD2 Guiding 7
Equipment Connection 7
Equipment Profiles 7
Camera Selection 7
Support for SBIG Dual-chip Cameras 8
ASCOM Camera Properties 9
Multiple Cameras of the Same Type 9
Mount Selection 9
Aux Mount Selection 10
Benefits of Using ASCOM (or INDI) connections 10
Adaptive Optics and Rotator Selections 10
Simulators 11
New-Profile-Wizard 11
Exposure Time and Star Selection 12
Multi-Star Guiding 13
Automatic Calibration 13
Conventional Mounts 13
Adaptive Optics Devices 14
Guiding 14
Dark Frames and Bad-pixel Maps 16
Introduction 16
Dark Frames 16
Bad-pixel Maps (Defect Maps) 17
Step-by-Step Guide to Refining a Bad-pixel Map 18
Reusing Dark Frames and Bad-pixel Maps 19
Visualization Tools 20
Overlays 20
Graphical Display 20
Stats 21
Star Profile and Target Displays 21
Adaptive Optics (AO) Graph 22
Dockable/Moveable Graphical Windows 22
Advanced Settings 23
Global Tab 23
Camera Tab 24
Guiding Tab 26
Algorithms Tab 29
Declination Backlash Compensation 30
Uni-directional Declination Guiding 31
Other Devices Tab 31
Guide Algorithms 33
Guiding Theory 33
Guide Algorithm Parameters 33
Tools and Utilities 37
Manual Guide 37
Auto-Select Star 37
Calibration Details 38
PHD2 Server 38
Dithering 39
Logging and Debug Output 39
Polar Alignment Tools 40
Drift Alignment Tool 41
Static Polar Alignment Tool 41
Polar Drift Alignment Tool 41
Lock Positions 41
Comet Tracking 42
Guiding Assistant 43
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 Star-Cross Tool 47
Meridian flip calibration Tool 48
Managing Equipment Profiles 48
Aux-Mount Connection using "Ask for coordinates" 48
Advanced Settings for the Simulators 49
Multiple Program Executions 50
Keyboard Shortcuts 50
Software Update 50
Checking for updates 50
Table of PHD2 keyboard shortcuts 51
Trouble-shooting and Analysis 52
Calibration and Mount Control Problems 52
Display Window Problems 55
Hot-pixel and Star-Selection Problems 56
Restoring a Working Baseline 56
Camera Timeout and Download Problems 56
Poor Guiding Performance 57
Alert Messages 57
Log Analysis 58
Guiding Log Contents 58
Problem Reporting 59
PHD2 Drift Alignment Tool 60
Preparation 60
Azimuth Alignment 60
Altitude Alignment 66
Using Bookmarks 68
Notes about ASCOM 68
PHD2 Static Polar Alignment (SPA) Tool 68
Automated Mode 68
Manual Mode 71
Using the Polar Alignment Overlay 74
PHD2 Polar Drift Alignment Tool 75

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Introduction
PHD2 is the second generation of Craig Stark's original PHD application. PHD became a fixture of the amateur astronomy community with more
than a quarter million downloads. From its inception, it has successfully embraced three seemingly conflicting objectives:
1. For the beginning or casual imager, to deliver ease of use and good guiding performance "out of the box"
2. For the experienced imager, to deliver sophisticated guiding algorithms, extensive options for tuning, and broad support for imaging
equipment
3. For all users, to consistently exhibit a commercial level of quality while being available free of charge
In order to extend PHD to more platforms and further expand its capabilities, Craig released his program to the open-source community, and
PHD2 is the direct result of that change. It has been substantially restructured to make it more extensible and supportable going forward. Now,
after over 5 years of independent development, PHD2 includes a substantial number of new features and refinements, many of which focus on
helping you achieve better guiding results. Users of PHD2 can be confident it will remain committed to the three objectives that made the original
application so successful.

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Main Screen
The PHD2 main window is designed for ease of use and clarity. Its intent is to support a quick and natural sequence of interactions to start and
control guiding. The basic steps for doing this are as follows:
1. Connect to your guide camera and mount
2. Start a sequence of guide exposures to see what stars are available in the field of view
3. Let PHD2 auto-select a suitable star and calibrate the guider
4. Continue guiding on the target star while using various display tools to see how things are going
5. Stop and resume guiding as necessary

The majority of the screen is taken up by the display of the star field from your guide camera. The display is automatically adjusted for size,
brightness, and contrast so you can view the available stars. However, these adjustments are done only for display purposes. Internally, PHD2
operates on the raw, un-adjusted data in order to maximize guiding accuracy. This display can also used to manually select a guide star by
clicking on it although it's better to use the 'Auto-select star' feature.. You can adjust the slider control to see even the faintest stars in the field.

Basic control
Near the bottom of the screen are the main controls. PHD2 is largely controlled by these buttons and sliders, with additional pull-down menus at
the top of the window for more detailed functions. Moving from left to right in the window, the primary buttons are as follows:
1. The USB connector icon - used to connect to your camera and mount devices
2. The Loop icon - used to start a sequence of repeated exposures with the guide camera ("looping"), with each resultant image (guide frame)
being displayed in the main window. If guiding is subsequently started, clicking on the 'loop' icon again will pause guiding while continuing to
take guide exposures.
3. The Auto-Select Star icon - used to trigger an automatic selection of the best guide star candidate in the field of view. This selection is done
quantitatively, taking many things into account - star saturation, minimum star size, signal-to-noise ratio, proximity to other stars, proximity to
the edge of the field, etc. The technique will nearly always make a better choice than you can manually even though the selected star may
appear quite faint.
4. The PHD2/Guide icon - used to start calibration, if needed, and then to start guiding on the selected star.
5. The Stop icon - used to stop both guiding and looping
To the right of the stop icon is a pull-down list of exposure durations (0.01s - 15s). You use this control to quickly set the guide camera's
exposure duration. If your camera does not support an exposure duration, PHD2 will do its best to emulate that duration. For example, if you use
a short-exposure webcam, your maximum true exposure duration might be only 1/30th of a second. If you select one second as the desired
exposure time, PHD2 will automatically acquire images for one second and stack them on the fly to create a composite image for guiding.
The next control to the right is a slider for adjusting screen stretch and contrast, essentially a "gamma" adjustment. PHD2 automatically adjusts the
display accounting for the darkest and brightest pixels in the image, and the slider is used to fine-tune the display to better see the stars in the field
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of view. This may be useful, for example, if you are trying to focus the guide camera for the first time and need to see the large, out-of-focus star
image. Moving the gamma slider only makes the display brighter or dimmer for your viewing. PHD2 always uses the raw pixels from the camera
for guiding, and moving the gamma slider has no effect on guiding. A display of "completely white" or "completely black" is usually an indication
that no stars are available in the field of view. The automatic gamma-stretching of the image is a very common source of confusion for users
because they don't adjust the gamma slider properly to see faint stars on the display. The stars that PHD2 auto-selects may appear to be overly
faint and inferior to bright stars you see in the display. These results are illusory because PHD2 can generally do a better job of selecting a guide
star than you can accomplish by eye. As a rule of thumb, if you've chosen a star whose name is known to you, it is almost certainly too bright to
be a good choice as a guide star.
Next to the gamma slider is the "brain button." This button brings up an Advanced Settings dialog for making detailed adjustments to PHD2's
guiding operations. An important design goal of the program is to minimize your need to change these parameters, but "the brain" is nothing to be
feared - there are adjustments available there that can improve your guiding results and make your life easier. Over a period of time, you should
take a look at this dialog and learn what it can do for you.
The rightmost control in this row is a "camera properties" button. Depending on the particular camera, this button may be enabled to provide
access to a configuration dialog unique to the camera. However, common camera properties such as gain and binning will normally be set in the
'Camera' tab of the PHD2 Advanced Settings dialog. If the button is disabled, any available properties can be set in the PHD2 Advanced Settings
dialog. With the newer class of guide cameras, this button is often disabled because it adds no capabilities beyond what is available in the PHD2
Advanced Settings dialog.

Menus
The pull-down menus above the main guider display are used to access a variety of functions. These are described in the Darks, Tools and
Utilities, and Visualization sections of this help document.

Status Bar

The status bar at the bottom of the main window is used to display messages and status information that will help you keep track of guiding
operations.

Near the center of the status bar are fields showing the current state of the guide star. If the SNR value drops below 10, its value will be shown in
yellow as a warning that you may encounter some 'lost-star' events. If the guide star is saturated, the field to the left of SNR will show 'Saturated'
in a red typeface.

To the right of the star status fields are two text fields showing the latest RA and Dec guide commands. These show the size of the guide pulse, the
guide star displacement size in pixels, and an arrow showing the direction. The arrows follow the usual compass conventions: Dec up/down
corresponds to north/south, RA left/right corresponds to west/east. All of this information is captured in the log files and displayed in the various
graphical tools, and those are what you should use for visualizing your guide performance. But these status fields may give you a quick visual clue
when something is behaving unusually.

The rightmost panels in the status bar show icons that give you visual clues about the current state of PHD2:. These icons are color-coded to give
you a dashboard view of current status and have the following meanings:

'Dark' - red means neither a dark library nor a bad-pixel map is being used, green means one or the other is in-use. If you're using a bad-pixel
map, the text will say 'BPM' rather than 'Dark'

'Cal' - shows the state of calibration. Red means the mount is currently uncalibrated, while yellow means there is a calibration but it isn't being
adjusted automatically to account for scope pointing position. This will happen when you aren't using either an ASCOM or 'aux' mount connection
in PHD2. If the icon is yellow, you will generally need to recalibrate when you move the scope to different declination positions.

"The Ball" - shows whether all the equipment in your profile has been successfully connected. If the ball is yellow, some components are not
connected, while green means everything is connected.

If you hover the mouse cursor over any of these status icons, you'll see details about the current state.

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Using PHD2 Guiding
There are five basic steps to start guiding.
1. Press the USB-icon button and connect to your guide camera and mount.
2. Pick an exposure duration from the drop-down list.
3. Hit the loop button and look at the available stars, adjusting focus if necessary. Move the mount or adjust the exposure duration as needed
to find a suitable guide star.
4. Click the 'Auto-Select Star' icon to choose the best guide star candidate.
5. Press the PHD2 Guide button.
Details of these operations will be described in the sections below.
Equipment Connection
Exposure Time and Star Selection
Calibration
Guiding

Equipment Connection
In order to begin guiding, PHD2 must first connect to your hardware: the guide camera, the mount, and, optionally, an 'aux' mount, an adaptive
optics (AO) device, or a rotator. When you click on the USB icon, you'll see a dialog that looks like this - the various choices in this dialog are
discussed below.

Equipment Profiles

At the top of the 'Connect Equipment' dialog are controls for managing equipment profiles. All of the guider settings in PHD2, default or
otherwise, are automatically stored as part of an equipment profile. If you have only one guiding setup - you use the same camera and guide scope
combination each time - you will only need one profile. But you may have multiple equipment configurations - for example, an off-axis-guiding
arrangement for a long focal length scope and a separate guide scope/camera configuration for a shorter focal length imaging scope. The PHD2
guide settings for those configurations are likely to be different, so you would want to use separate equipment profiles The controls at the top of
the 'Connect Equipment' dialog let you choose the profile you want to use and to create/edit/remove profiles as you see fit. When you select a
profile and connect to its associated equipment, all of the settings last used with that profile are automatically reloaded. Once you've established
the profiles you need - perhaps only the default one - you can simply click on the 'Connect All' button and you're ready to move ahead. If you
already have a suitable default equipment profile and you simply want to connect to the equipment just as before, you can do a <shift>-click on the
main screen 'USB' button and PHD2 will automatically re-connect to your hardware.

For new users especially, the most important option in the 'Manage Profiles' list is the New Profile Wizard. Using this wizard is the easiest way to
be sure you've specified all the required parameters and have a coherent profile definition for your gear.

Camera Selection

The Camera drop-down list shows all the camera types currently supported by PHD2. In all cases, the OS-level drivers for the camera must be
installed correctly in order for PHD2 to connect to the device. If the camera uses an ASCOM interface, you'll also need to install the
corresponding ASCOM driver for the camera. If you don't see your ASCOM-compatible camera shown in the drop-down list, you probably
don't have the ASCOM driver installed. Neither the ASCOM nor OS-level drivers are included with PHD2, so they must be located,
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downloaded, and installed separately. For non-ASCOM cameras, the PHD2 distribution does include the additional application libraries needed
by PHD2 to use the camera. In some cases, the camera may have both ASCOM and proprietary interfaces and you're free to choose whichever
you prefer. In some cases, the two different versions may operate the camera in a slightly different way or expose different sets of camera
properties.

It is not practical to provide an exhaustive list of cameras that are supported by PHD2. In many cases, camera vendors extend their product lines
by updating their lower-level drivers without having to change the application libraries used by PHD2. In those cases, we aren't aware of the
changes unless a user reports problems. The list shown below should be interpreted as follows:
1. If the camera vendor is completely absent, it is unlikely that the camera is supported, or it may only be supported using a web-cam interface
2. If the camera model is shown in the list, it is supported unless there are unresolved problems with the vendor's drivers
3. If the specific camera model is absent but earlier models are shown, it is likely the camera is supported
4. If the camera uses an ASCOM interface, it is supported

Since the PHD2 download is free, the simplest course of action is to install it and see if your camera is shown in the PHD2 drop-down list.
Alternatively, you can check for camera support info in the Wiki on the PHD2 Google forum:
https://github.com/OpenPHDGuiding/phd2/wiki/CameraSupport

Finally, you can always post a message on the open-phd-guiding forum asking if anyone has experience with the camera.

Baseline list of supported cameras:

Windows:
ASCOM v5/6 compliant cameras
Altair
Atik 16 series, color or monochrome
Atik Gen 3 color or monochrome
CCD-Labs Q-Guider
Fishcamp Starfish
iNova PLC-M
MagZero MZ-5
Meade DSI series: I-III, color and monochrome
OpenCV
Orion StarShoot DSCI
Orion Starshoot Autoguider
Orion Starshoot Planetary Imager and Autoguider
QHY 5-II
QHY 5L-II
SAC4-2
SBIG
SBIG rotator
Starlight Xpress SXF / SXVF / Lodestar
ToupTek
Webcams (LXUSB, parallel, serial, OpenCV, WDM)
ZWO ASI
Mac:
Fishcamp Starfish
KWIQGuider
Meade DSI series: I-III, color and monochrome
Orion Starshoot Autoguider
SBIG
Starlight XPress SXV
The Imaging Source (DCAM Firewire)
ZWO ASI

Support for SBIG Dual-chip Cameras

Many cameras from the Santa Barbara Instrument Group (SBIG) have two sensors - a primary one for imaging and a second, smaller one for
guiding. While the two sensors are physically separate, they share electronics inside the camera and more importantly, share a single USB data
link to the computer. This means that downloading of data from the two sensors must be coordinated - you can't retrieve a guider image while an
image from the main sensor is being downloaded. Beyond that, Windows will only allow one application at a time to connect to the camera over
the single USB link. These are physical and architectural restrictions that can't be circumvented by PHD2. However, it is possible for the camera-
controlling (image capture) application to implement an interface for PHD2 to get data from the guide chip - essentially, a "side door" mechanism

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that won't violate any of the above rules. With this arrangement, the image capture application is acting as a traffic cop to coordinate access to the
two camera sensors. At the time of this writing (2019), the only imaging application that does this is Sequence Generator Pro (SGP). If you use
SGP as your main imaging application, you can also use their "SGP API Guider" module, which allows PHD2 to access the guide chip on the
SBIG camera.

ASCOM Camera Properties

If you choose an ASCOM camera, you'll also be able to access the ASCOM setup dialog for that camera by clicking on the properties button
immediately to the left of the 'Connect' button:

Depending on the camera, this may provide access to properties that are not controlled by PHD2.

Multiple Cameras of the Same Type

If your computer is connected to multiple cameras from the same manufacturer, you'll usually need to specify which camera should be used by
PHD2. You can do that by clicking on the 'fork' button to the right of the camera drop-down list:

Clicking this button will show a list of the available cameras and you can choose the one you want. PHD2 will remember the choice and save it as
part of your equipment profile, so you should only need to do this once. An alternative is to simply connect one of the cameras, the intended guide
camera, at the time you build your equipment profile.

Mount Selection

The Mount drop-down list displays options for connecting to your mount. There are generally two ways to do this:
1. Use an ASCOM-compatible (or INDI) telescope driver that sends guide commands to the mount over a serial cable (or more commonly,
a USB/Serial connection)
2. Use the ST-4 compatible guide port interface on the mount with a specialized cable and an intermediate device like a camera or a
Shoestring box
The ASCOM interface relies on third-party drivers to communicate with the mount. These drivers are available from the ASCOM web site
(ASCOM Standards) or from the mount manufacturer - they are not distributed with PHD2. So the drop-down list will be populated by only
those ASCOM drivers you already have installed on your system. The ASCOM driver must support the 'PulseGuide' interface, which has been a
requirement for ASCOM compliance for many years and is widely supported. With this type of mount control, guide commands are sent from
PHD2 to the mount over the serial interface. The high-level PHD2 guide commands (e.g. "Move west 500 mSec") are translated by the mount
firmware into the appropriate motor control signals to execute the command. With the ASCOM interface, PHD2 can also obtain the pointing
position of the mount, especially the declination and side-of-pier, which can be used as factors in guider calibration and provide greatly improved
ease-of-use.
The "Guide-port" interfaces use a specialized, hardware-level control port available on most mounts. To use this type of interface, there must be
another device in the link between PHD2 and the mount:
1. Any of the guide cameras which have an ST-4 compatible "on-camera" guider interface. Use the 'on camera' mount choice for these setups.
2. Any of the Shoestring GP-xxx devices
3. A supported AO device with a guide port interface
With this style of interface, PHD2 guide commands like "Move west 500 mSec" are translated by the intermediate device (camera, Shoestring
box, AO) into electrical signals necessary to drive the mount motor for the correct length of time.
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Aux Mount Selection

If you have selected an ST-4 style of guiding in the 'mount' section, that interface cannot be used to query the pointing position of the telescope.
As a consequence, guider calibration won't be automatically adjusted for declination, nor will it be automatically flipped when the side-of-pier
changes. You can restore these features by specifying an "aux" mount connection that will be used to get the telescope pointing information. An
example is shown below:

For Windows users, the "aux" mount can use any of the ASCOM-compatible mount drivers, while Linux users can take advantage of INDI
drivers. The "aux" mount choice will be used only if the primary mount interface cannot return pointing information - it will otherwise be ignored.
Note: some mounts (e.g. Celestron and iOptron) have a separate hardware port also labeled 'Aux' - DO NOT USE THIS for guiding - it is
completely unrelated to the 'Aux' connection in PHD2. The last entry in the list of 'Aux mount' connections is labeled "Ask for coordinates." This
can provide a rudimentary aux-mount facility if you can't use an ASCOM or INDI connection to your mount. If you need to pursue this option,
you can read about the details in the Tools section.

Most ASCOM mount drivers use a serial port interface, so the driver expects to use one of the Windows 'COM' ports. Since most personal
computers no longer have serial port connectors, you can use one of the USB ports and a USB-serial adapter. The software that comes with the
USB-serial adapter will create a software COM port, and that's the one you'll use with the ASCOM driver. The first time you connect to the
mount with ASCOM (either as 'mount' or 'aux-mount'), you'll need to tell the driver which COM port to use. That's part of the driver's setup
dialog, and you can quickly open that window by clicking on the 'properties' icon just to the left of the 'Connect' button in the above image. Once
you've done this, the COM port will be saved as part of the equipment profile

Benefits of Using ASCOM (or INDI) connections

If you're running on a Windows platform, you'll probably be better off using an ASCOM connection for guiding your mount. On other operating
systems, your best choice is likely to be an INDI connection if one is available. This advice may be contrary to some old-school experience or
folklore on the Web and probably isn't what you'll hear from the manufacturer of the guide camera. But the benefits of doing so with PHD2 are
substantial, and you should use this alternative unless you have specific and credible information against it. Here are some of the primary benefits:
1. A drastic reduction in the number of re-calibrations you'll need to perform. Changing targets will not require another calibration because
PHD2 can know where the scope is pointing and automatically make adjustments to the guider calibration. Most users get a good
calibration and then re-use it until they make hardware changes of some kind.
2. Automatic adjustment for meridian flips - no need to remember to manually flip the calibration data.
3. Automatic adjustment of RA calibration to handle targets in different parts of the sky (declination compensation)
4. Elimination of the ST-4 guide cable as a point of failure - this is a surprisingly common problem because the cables can be damaged or
confused with similar-looking cables (e.g. telephone cables)
5. Elimination of a moving cable that can snag, drag, or bind as the scope is moved around.
6. Improved ability for PHD2 to sanity-check calibration results and warn of possible problems before you waste hours of imaging time.
7. Better diagnostic and trouble-shooting information, which is particularly helpful if you need to ask for assistance
8. Availability of scope-slewing options during drift alignment which can further speed the process of polar alignment
If you have an older mount built before 2005 or thereabouts, it may not have firmware-level support for ASCOM pulse guiding. In those cases,
you may get better guiding results using the ST-4 guiding interface. If you're in doubt, check the documentation for your mount or ask on one of
the forums about pulse-guide support. Even then, you can use ASCOM for the PHD2 "aux-mount" connection and get most of the benefits listed
above. A common misconception, frequently seen on Web forums, is that ST-4 guiding is hardware-based and thus more accurate or efficient.
For any of the modern mounts you're likely to encounter, this is no longer true - there will always be software running at each end of the cable, just
like ASCOM guiding. The bottom line is this: if you have an ASCOM or Indi driver available for your mount, you should probably use it.

Adaptive Optics and Rotator Selections

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With PHD2, you now have the option of controlling the Starlight Xpress adaptive optics unit and/or any of several ASCOM-compatible camera
rotators These can be specified by clicking on the 'More Equipment..." button in the above dialog:

If you don't have these devices, just leave the selections at 'None.' If these devices are connected, you'll see additional tabs in the 'Advanced
Settings' dialog that provide access to various device-related properties. PHD2 does not control a rotator, but it will read the current angle setting
from the rotator and adjust the guiding calibration if needed.

Simulators

All of the PHD2 devices - camera, mount, AO, rotator - include built-in simulators. Don't confuse these with any of the ASCOM simulators
which may be installed on your system - those will have 'ASCOM' in their names. Although you can connect to the ASCOM simulators, they
don't provide the necessary feedback to PHD2 for guiding and calibration. As a result, they're only useful for limited types of testing and
experimentation. But you can use the built-in simulators to explore how PHD2 works and to decide how you want to use the program. There's
no reason to waste valuable dark-sky time learning to use PHD2! Virtually all of PHD2's features, including full calibration and all the graphical
display options, will work properly when the built-in device simulators are used. You'll even see fairly realistic guiding performance to give you
some idea of what to expect in the field. To get started using the simulators, choose 'Simulator' for the camera type and 'On-camera' for the
Mount type.

That said, the simulators are not useful for trouble-shooting any problems you encounter with your real mount. Both the camera and the mount
must be real devices in order to diagnose problems or otherwise get your gear calibrated and working. In that sense, what you see when using the
simulators is realistic but "fake" behavior. The simulators can be useful in some cases for reproducing PHD2 application problems, but not for
anything having to do with your actual guiding equipment.

New-Profile-Wizard

The best way to create a new profile is to use the "Wizard" capability. The wizard takes you through a sequence of windows that explain the
various settings and help you decide how to set them. It will also calculate baseline algorithm settings that are likely to work reasonably well for
your set-up. Creating a profile this way is faster and less error-prone than doing it by hand in the 'Connect Equipment' dialog. When you run
PHD2 for the first time on your system, this wizard will be automatically launched. Subsequently, you can use the new-profile wizard by clicking
on the 'Manage Profiles' field in the 'Connect Equipment' dialog, then choosing 'New using wizard...'.

The wizard asks a number of questions that are important for getting your profile built correctly. The explanatory text in each pane of the wizard
should make clear what is being asked and what needs to be done. But here are some additional tips to help you through the process:

1. Connection Options: As you make selections for the various devices, you will usually see a prompt asking if the device is already
connected and ready to communicate with PHD2. If you say 'yes', PHD2 will try to connect and then fill in some of the data fields with
information read from the device. Saying 'no' simply means you'll have to enter the data by hand. If PHD2 tries to connect with the device
and fails, you'll still be able to proceed by just entering the data manually. Device-connection in the wizard is basically a convenience
feature that makes it easier to fill in the fields with accurate values. You won't see the prompt if PHD2 already knows the device can't return
useful information - for example, if the mount choice is 'on-camera.'
2. Camera connection pane: unbinned pixel size. If you said 'yes' to the connection prompt, this information will usually be filled in
automatically and the control will be disabled. If you said 'no' or if the device doesn't report its pixel-size, you'll need to enter the value by
hand. You should be able to get the unbinned pixel size from the camera spec sheet or the manufacturer's web site. If the pixels aren't

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 square, just specify the larger dimension or the average value if you prefer. This won't have any effect on your actual guiding results, but it
will allow PHD2 to know the image-scale for your set-up. This is used for setting baseline guiding parameters, doing sanity-checks on
calibrations, reporting guiding performance, and getting support on our forum..
3. Camera connection pane: binning level. If your guide camera supports binning (many do not), you can specify what level of binning
you want to use for this equipment profile. If you want to use the same equipment set-up with different binning levels, it's best to create
separate profiles for each binning value. If your guide camera has very small pixels and you have also specified a long focal length, you may
see a 'warning' icon next to the Pixel Scale field. That is telling you that the specified image scale is probably too small and you should bin
the camera if possible.
4. Camera connection pane: guide scope focal length. This seems to be a common place for mistakes, so it's worth being careful and
getting it right. The correct value is not the aperture of the guide scope, it is the focal length. So, for example, if you're guiding with a
50mm finder scope, the focal length will not be 50mm - it will probably be something closer to 150-175mm. A 60-80mm refractor guide
scope will probably have a focal length in the range of 240-500mm, not 60-80mm. Similarly, if you're guiding with an OAG on your main
imaging scope, the focal length will be that of the main scope. In some cases, you may be using a small threaded focal reducer on the guide
camera, so that must also be taken into account. Like the pixel-size entry, the focal length doesn't demand a great deal of precision, but you
should get as close as you can. Otherwise, the performance numbers may not reflect your actual results and the baseline guiding parameters
may be sub-optimal.
5. Mount connection pane: mount guide speed. This is another area that seems to cause confusion. The guide speed is a parameter
set in the mount or in the mount driver, it's not something controlled by PHD2. PHD2 never sets the mount guide speed, it only reads it.
It is usually expressed as a multiple of the sidereal rate and is typically in the range of 0.5x - 1x sidereal. Despite what you may read
elsewhere, it's usually best to use guide speeds in this range rather than much lower speeds. Higher guide speeds can help to clear backlash
more quickly and may help to overcome stiction problems. If you say 'yes' to the connection option prompt, PHD2 will attempt to read the
current guide speed from the mount. If this fails for some reason, you'll need to enter the guide speed manually. PHD2 uses this value to
automatically set the calibration step-size and to aid in checking calibration results; but the guide speed information is not important for the
actual guiding. If you're using different guide speeds on the RA and Dec axes, enter the larger value. If you really can't determine what the
guide speed settings are in the mount, leave the setting at the default value of 0.5X. This pane also has a checkbox regarding the presence
of high-precision encoders in the mount. These devices are somewhat rare but are sometimes included on expensive, high-precision
mounts, and you are likely to know if you have them. Most users will leave this box unchecked.

In the last pane of the wizard dialog, you're given two options: 1) To automatically restore the PHD2 calibration whenever the profile is loaded and
2) to immediately build a dark library when the new profile is saved and the wizard completes. The first option is only presented if your profile
uses an ASCOM or INDI mount. It is a convenience item especially for users with permanent setups. You can also use this option if you can
insure that the guide camera orientation in its adapter tube remains the same from one night to the next. If you're in doubt or don't want to bother
with how the guide camera is oriented, leave the box unchecked. You should always select the option to build a dark library unless you already
have a compatible dark library that you're going to import from a different profile. If you are changing cameras and want to keep the dark libraries
and bad-pixel maps associated with the old camera, you should create a separate profile for the new camera. When a camera selection is changed
in an existing profile, the previously built dark library and bad-pixel map data will no longer be usable. That also applies to using the same camera
with different binning values. Setups using different binning factors should be kept in separate profiles because the dark library and bad-pixel maps
depend on the binning factor.

Exposure Time and Star Selection

The guide star is selected while "looping" is active. The best approach is to let PHD2 Auto-select the guide star for you by clicking on the 'Auto-
Select Star' icon in the main window. In nearly all cases, it will do a better job of star selection than you can do manually because it takes a
number of things into account - for example, lack of saturation, qualification as a "real" star, proximity to other stars and to the edge of the field,
etc. If you choose to not use the auto-select feature, you can select a guide star candidate by clicking on it. After you do this, a green box will
appear to frame the star. If you pick a star that is too bright (saturated), the status bar will show a red 'SAT' label and you should choose a
fainter star. You should adjust the gamma slider to the left to see fainter stars. Most new users are fooled by this and often choose the brightest
star they happen to see in the field of view. But that choice is often a saturated star, not a good choice for auto-guiding. The choice of exposure
time will depend entirely on your equipment, sky conditions, and the available stars. The exposure time you choose has several implications:
1. It affects the signal strength (brightness) of the selected star - a brighter star will stand out better from the background and will generally
produce better guiding results so long as it is not saturated.
2. It also determines the frequency with which guide commands are sent to the mount - guide commands cannot be sent any more frequently
than once for each exposure cycle. Some mounts need frequent small guiding adjustments while others do not - you may need to
experiment to understand what works best for your situation.
3. It has a strong effect on the sensitivity of the guide algorithms to seeing conditions. As the exposure time is increased up through 2-4
seconds, the effects of seeing are smoothed out. The camera is essentially averaging out the larger, high-frequency seeing movements, so
the guide algorithms have less difficulty distinguishing "seeing jitter" from actual guide star displacements that need to be corrected. This is
particularly noticeable if you are guiding with a long focal length setup. Of course, the convenience of using longer exposures must be traded
off against the need for the mount to get frequent corrections. For mounts that have too many high-frequency errors in RA, you may need
to work with 1-second exposures.
As a starting point, try using exposure durations in the range of one to three seconds. If you want to de-select a star without choosing another one,
you can do a shift-click anywhere on the image display window. If you are just starting with this equipment set-up, you'll probably need to focus

12
the guide camera - doing so is important for good guiding. You can use the Star Profile tool to help with that process or whatever other focusing
tool you are comfortable - a focusing mask, a camera app like SharpCap, etc.. If you're using a small guide scope, like a finder-scope, the focus
may react strongly to small adjustments. It's important to spend the time to get a good focus because a poorly focused guide star can lead to many
other problems. The camera exposure control displays a wide range of pre-set exposure times. Exposure times smaller than one second are
intended for use with adaptive optics devices or in other special situations - they are generally not appropriate for use with typical guide camera
set-ups. There is also a 'custom' exposure option at the bottom of the list that lets you specify a value not already displayed. Again, this is
intended for special applications, for example where an unusually long exposure time is needed.

There is also an Auto exposure time selection available. When exposure is set to Auto, PHD2 will attempt to adjust the exposure to keep the
selected guide star at a constant signal-to-noise ratio (SNR) value while working within the exposure limits you choose. This is a specialized
measurement used by PHD2 to determine how well the star can be distinguished from the background - it is similar but not identical to the signal-
to-noise ratio used in photometry. The Auto setting is intended for AO users who want to minimize exposure time without losing the guide star or
for use in automated imaging operations. Automation involves slewing and subsequent unattended guide star selection, and failure to find a bright-
enough star will cause the automated session to fail. In such cases, a "long" exposure time may be preferable to finding no guide star at all. The
settings to control Auto-exposure are on the Camera Tab of the Advanced Settings dialog.

Multi-Star Guiding
Some guiding configurations can benefit from guiding on multiple stars rather than just one. This results in using a weighted average centroid
position of multiple stars rather than just the centroid of a single star. Multi-star guiding is enabled using a check-box on the Guiding Tab of the
Advanced Settings dialog. When this option is enabled, the Auto-select function will identify up to 12 stars in the field of view that have adequate
SNR. No more than 9 of these will be used at any one time, but the remainder will be used to replace secondary stars that are lost or rejected for
some reason. The "primary" star is the single best candidate, the same one that will be selected if multi-star guiding is disabled. As guiding
proceeds, some of the secondary stars may be rejected because they are too dim or have drifted outside the field of view. This is of no concern,
the multi-star guiding algorithm handles the secondary list automatically. When multi-star guiding is active, the PHD2 image display will show the
usual rectangle around the primary star and circles around the secondary stars. All other UI features associated with a guide star - brightness
properties, SNR, FWHM, etc - relate to the primary star, not the entire list. Multi-star guiding can be enabled or disabled while guiding is active.
However, enabling the feature will force another 'auto-select' procedure. The multi-star algorithm uses the secondary stars to refine the centroid
position and reduce its volatility, so there is essentially no way for it to degrade guiding performance. Whether it produces a material benefit to
your overall guiding will depend on many factors including image scale, star and background sky brightness, star size, focus, and camera noise.
Because of the way the algorithm is implemented, your best option will be to try it and decide for yourself. Note: if you don't use the auto-
select function and instead choose a guide star manually, multi-star guiding will be inactive.

Automatic Calibration
Conventional Mounts

Two things need to be measured by PHD2 as part of guider calibration:

1. The angle of the camera relative to the telescope axes
2. The length of the guide pulse needed to move the telescope by a specific amount
PHD2 handles these measurements automatically by sending guide pulses to the mount and watching how far and in which direction the star moves
between guide camera images. This process begins after you have selected a star and then clicked on the PHD2/Guide icon button. Yellow
cross-hairs will appear over the original location of your guide star and PHD2 will start to move the mount in various directions, tracking how the
star moves as a function of what move commands were sent to the mount. The status bar will display the commands as they are sent to the mount,
along with the incremental movements of the guide star relative to its starting position. PHD2 will do this on both axes, first moving east and west,
then north and south. PHD2 wants to move the star up to 25 pixels in each direction in order to get an accurate calibration. Once this is
complete, the crosshairs will turn green and guiding will start automatically.

Although PHD2 moves the guide star in all four directions, only the west and north movements are actually used to compute the guide rates and
camera angle. The east and south moves are used only to restore the star roughly to its starting position. Before the north moves are begun, you
will see a sequence of pulses that are intended to clear backlash. PHD2 takes only a moderate approach to clearing this backlash, watching for a
clear pattern of movement in a single direction with no reversals. If your mount has a large amount of Dec backlash or you're guiding at a long
focal length in poor seeing conditions, this phase of calibration may not remove all the backlash. Your best option for avoiding this problem is to
make sure the last move of the mount prior to the calibration is north. You can accomplish this with a short slew or by using the hand-controller
to get the mount moving north as evidenced by obvious movement of the guide star in the PHD2 display. If the backlash is not cleared
adequately, the computed declination rate may be too low, a situation that is discussed further in the Tools and Utilities section. You may also see
that the south pulses leave the guide star well-short of its starting position - this is another visual clue that you have significant declination backlash
in your mount. If you see evidence of sizable backlash, you can run the Guiding Assistant tool and measure it directly.

In most cases, calibration will complete automatically without any user involvement. If the mount doesn't move sufficiently in the west or north
directions, you will get an alert saying the calibration has "failed". Failures of this type are pretty uncommon but they can occur if some part of
the hardware is simply not working (e.g. a bad guide cable). Unless you see a "failed" message, the calibration actually completed. You may see
other alert messages advising you that the calibration results look suspect or show mount behavior that is likely to cause problems during guiding.

13
 These are advisory messages only, they don't mean that the calibration itself failed. If you get frequent messages like this during calibration, you
should consult the trouble-shooting section of the manual.

If you're using an ASCOM (or Indi) connection for either the 'mount' or 'aux-mount', a good calibration can be re-used for a long time, and that is
the preferred way to operate. These connection options allow PHD2 to know where the telescope is pointing, so a calibration done at one point
in the sky will be automatically adjusted as you slew to different targets. The old method of having to re-calibrate whenever you slewed the scope
or switched the side-of-pier is a thing of the past so long as PHD2 has pointing information. With this type of set-up, you would only re-calibrate if
you rotate the position of the guide camera by more than a few degrees or make other major changes to the hardware configuration. In general,
the best practice is to get a good calibration within about +/- 20 degrees of the celestial equator and high enough in the sky to avoid major seeing
(turbulence) problems. If you chose 'auto-restore calibration' when you built your profile or chose that option in the Guiding tab of the Advanced
Settings dialog, you can simply connect to your gear, choose a guide star, then begin guiding immediately. Beginners will probably have better
success if they do a fresh calibration at the start of each night's session. Finally, if you're using an instrument rotator as part of your equipment
profile, PHD2 can use the 'Rotator' connection to adjust the calibration data based on the angular position of the guide camera - one less reason
for re-doing a calibration.

You can always review the results of your last calibration by using the 'Tools' menu and clicking on 'Review Calibration Data' That will open a
dialog that shows a graphical representation of the mount's movements along with the values that were computed for guiding your mount. This
window is described elsewhere in the Calibration Details section of the help file. As a quick quality check, you can open this window and confirm
that 1) the RA and Dec lines are roughly perpendicular and 2) the plotted points are roughly linear with no significant curves, bends, clumping of
points, or reversals in direction. If you do see these kinds of odd patterns in the graph, you should probably re-do the calibration. Even with
high-end mounts, calibrations can occasionally go awry because of environmental conditions, especially wind and bad seeing.

After a calibration is completed, PHD2 will "sanity check" the results to be sure the calculations at least look reasonable. If they don't, you will see
an advisory message at the top of the main window that describes the calibration result that looks questionable. You can choose to ignore the alert
or click on 'Details' to get more information. It is generally advisable to pay attention to these alerts because there is no point in trying to guide
using a significantly bad calibration.

Adaptive Optics Devices

If you are using an adaptive optics device, there are actually two calibration processes that must complete. The first handles calibration of the
tip/tilt element in the AO and calculates the magnitude and direction of the adjustments as they relate to displacements of the guide star. The
second calibration is the one described above, dealing with guide commands that need to be sent to the mount. Known as "bump" commands,
these will be issued when the guide star has moved beyond the range of corrections that can be achieved with the AO alone.

Guiding
Once guiding has begun, diagnostic messages will be displayed in the status bar to show what guide commands are being sent to the mount. PHD2
will continue guiding until you click on the 'Stop' icon. To resume guiding, simply start looping exposures again, auto-select your star, and click on
the 'Guide' button. You will not need to repeat the calibration in order to resume guiding. In some cases, PHD2 may lose the guide star and you'll
be alerted by an audible beep and flashing orange crosshairs. There are several reasons this might occur:
1. Something may be obscuring the star - clouds, the observatory roof, a tree, etc.
2. The star may have abruptly moved out of the tracking rectangle because something shifted in the mount/camera/cabling infrastructure -
cable snags can cause this
3. The star may have "faded" for some other reason, perhaps because it is overly faint or the camera is not well-focused
Obviously, you'll need to identify the source of the problem and fix it. However, it's important to understand that PHD2 will not start moving the
telescope around in an attempt to relocate the guide star. It will simply continue to take exposures and look for the guide star to reappear within
the bounds of the current tracking rectangle. When you first start guiding, you may see an 'alert' dialog at the top of the window if no dark library
or bad-pixel map is being used. You can choose to ignore this warning and continue with guiding, but you are likely to get better results if you
spend the few minutes needed to construct a dark library for future use.

If you are using a German equatorial mount (GEM), you will usually have to do a "meridian flip" around the time your image target crosses the
meridian. This means you will move the telescope around to the opposite side of the pier and then resume imaging. Doing this invalidates the
original calibration, typically because the declination directions are now reversed. If you are using an ASCOM (or 'aux' ) mount interface, your
calibration will be adjusted automatically and you can simply resume guiding (assuming you haven't also rotated the camera or focuser). If you
aren't using an interface that returns pointing position, you will need to take action to adjust the guider calibration. You can, of course, simply do
another calibration on the current side of the pier, a process that will typically take only a couple of minutes. Or, you can use the pull-down menu
item under 'Tools/Modify Calibration' to "flip calibration data" and then resume guiding immediately. Note: 'flip calibration data' will have no effect
if PHD2 is using an ASCOM or 'aux-mount' connection.

In some cases, you may want to force a re-calibration. For example, you may have rotated the guide camera as part of resolving a cable problem.
You can do this by clicking on the 'Brain button', moving to the 'Guiding' tab, and clicking the 'Clear mount calibration' checkbox. Or, you can
simply do a <shift>click on the 'Guide' button on the main screen and PHD2 will start a calibration run.

14
Once you have started guiding, you will almost certainly want to know how things are going. You can of course watch the star in the guide camera
display but in many cases you won't be able to see all the small adjustments that are taking place. But PHD2 provides many tools for measuring
and displaying your performance, as described in the Visualization section. Several of the guiding algorithms have limit settings for the maximum
guide correction that can be issued with a single command. If these values are smaller than what is needed to correct the mount's position, you will
see an alert dialog at the top of the main window advising you of the situation. If this is a recurring problem and you haven't reduced the max-
move parameters below their default values, the source of the problem probably lies with the mount. .

15
Dark Frames and Bad-pixel Maps

Introduction
Cameras used for guiding are typically not temperature-regulated and may produce images that appear quite noisy. As a result, guide exposures
frequently show obvious defects in the form of hot (or "warm") pixels or regions with spurious brightness levels. If there are too many of these
defects, you may have trouble identifying and selecting a good guide star - trying to calibrate on a hot pixel is a common problem for beginners.
Even after guiding has begun, a spurious hot pixel close to the guide star can disrupt the calculations needed for smooth guiding and may cause the
software to "jump" between the real star and the hot pixel. These sorts of problems can be mitigated by using either of two approaches in PHD2:
dark frames and bad pixel maps. All functions related to dark frames and bad-pixel maps are located under the top-level 'Darks' menu.

Dark Frames
PHD2 will build and use a library of dark frames that match the range of exposures you use for guiding. Once the library is built, it will be saved
automatically and will be available for use across multiple PHD2 sessions. As a result, you can spend a modest amount of time to build a good
dark library, then use that library for an extended period of time. Once you have connected to your camera, you can build a dark library from the
'Dark Library...' item under the top-level 'Darks' menu. That will start a dialog that looks like this:

You use the two controls at the top to specify the minimum and maximum exposure times that will be used to acquire dark frames. The starting,
ending, and intermediate values match the exposure times used in the main PHD2 window, so you can acquire dark frames that will match any
exposure time you choose for guiding. The third control specifies the number of dark frames that will be acquired and averaged for each exposure
time. The averaged image is referred to as a "master dark frame." Historically, PHD has used 5 dark frames for this purpose, but you may want
to increase that number to improve the quality of the master dark frame. You can also add a note or comment if you wish - this will be embedded
in the header of the master dark frames for later reference.

The two radio buttons above the Notes field let you specify whether you want to modify/extend your current dark library or build a new library
from scratch. If you've gotten alert messages saying the dark library must be rebuilt, you should choose the 'Create entirely new dark library'
option. This insures that all of the master dark images match the format of the camera you're currently using. Otherwise, you can simply refresh or
expand the current dark library by taking new dark frames at the specified exposure times

Once you've set your parameters, click on 'Start' to begin the process. If your guide camera does not have a shutter - most do not - you'll be
prompted by PHD2 to cover the guide scope. To get the best results, be sure there is no light leakage into the guide camera - doing this in daylight
is not likely to work well. PHD2 will systematically work through the range of exposure times you've chosen, taking the specified number of
frames for each exposure time. Progress will be displayed on the status bar at the bottom of the window, so you can see where you are in the
overall process. Once you've started the process, the 'Cancel' button above will change to a 'Stop' button. You can click on this if something
goes wrong or you want to change the parameters before the entire sequence completes. Stopping in this way will discard whatever data has
already been collected, so you'll need to make your corrections and then restart the process. Once all the frames have been collected, PHD2 will
compute the master dark frames, store them in a dark library data file, then show a message box summarizing the results. If your camera has no
shutter, you'll also be prompted to uncover the guide scope so you can return to normal imaging.
16
Once your dark library has been built, you control its use by the 'Use Dark Library' item under the 'Darks' menu. The checkbox on the menu item
will toggle on or off each time you click on it. The setting of the item is retained across program executions, so if you choose to leave the menu
item checked, PHD2 will automatically load the dark library and resume its use the next time you run the application. The dark library itself is
retained on disk until you build a new library, so you can freely change the setting on the 'Use Dark Library' menu item without loss of any data. If
you are using a dark library and there is no master dark frame that exactly matches your guide exposure time, PHD2 will use the nearest fit.
However, you are encouraged to obtain matching master dark frames for best results. If you have a dark library that has missing exposure times,
you can simply acquire the missing data and it will be added to the existing dark library - there is no need to start over. By changing the setting of
the 'Use Dark Library' menu item, you'll be able to see the effect of using the dark library and determine whether your guider images are sufficiently
improved.

Remember that a dark library is associated with a particular camera and binning level. PHD2 will check to be sure that the dark library matches
the camera you are currently using. If it does not, you will see an alert message telling you the dark library can't be used and must be rebuilt. This
can happen when you've changed cameras inside an existing equipment profile, something you shouldn't do unless you have upgraded your guide
camera and have no plan to return to using the old camera.

Bad-pixel Maps (Defect Maps)

For some guide cameras, dark frames don't do an adequate job of removing the defective pixels that are visible in the guide frame. In those
situations, you can probably get better results by building and using a bad-pixel map. This approach directly measures and compensates for
specific areas of the sensor that produce false signal (hot/stuck pixels) or don't respond correctly to incoming light (cold pixels). Such a "map" is
created by taking a sequence of comparatively long dark exposures (e.g. 15 seconds), averaging them, then statistically analyzing the resultant
frame to identify the locations of defective pixels. These pixel locations are saved for future use. During normal guiding, each of these pixel
locations on the guide image is replaced by a statistical sample of the surrounding pixels, thus eliminating all or most of the effect of the "bad" pixel.
The final result is usually an image with a smoother background and fewer obvious defects. For any defects that remain, PHD2 also provides a
way for you to manually click on bad pixel locations and add them to the map. This entire process of obtaining and analyzing dark frames is
handled for you by PHD2, so it's easy to build a bad-pixel map.

Building a bad-pixel map is done by clicking on the 'Bad Pixel Map...' item under the top-level 'Darks' menu. If you are doing this for the first
time, you will be prompted to obtain a sequence of dark frames for analyzing your camera sensor and building the map:

This is a slightly different version of the dialog used for obtaining dark frames, described in the previous section. Because the analysis is based on
statistics, you should use relatively long exposure times (> 10 sec) and at least 10 frames. Since the bad-pixel map can be re-used for fairly long
time periods, you won't have to repeat this operation very often, and it's worth spending some time to get higher quality data.

Once the dark frames have been captured, PHD2 will compute the statistics and identify an initial set of defective or suspect pixel locations. After
a short delay, you'll then see a dialog that looks something like this:

17
The 'General Information' section shows a summary of the statistics computed by PHD2 during the identification of bad pixel locations. Normally,
you won't need to look at these, and you can hide this portion of the display by clearing the 'Show Master Dark Details' checkbox. The "Results"
group shows the counts for hot and cold pixels based on the current settings of the two "Aggressiveness" sliders below them. If you're doing this
for the first time, the aggressiveness sliders will be set at their default values, 75 within the range of 0 to 100. You'll need to experiment or make
some judgment about whether the counts look reasonable based on what you see on your normal guide frames. If you adjust the aggressiveness
sliders left and right, you'll see the hot and cold pixel counts change. The sliders control how "aggressive" PHD2 should be in identifying suspect
pixels and flagging them as being defective - so higher aggressiveness settings will result in higher pixel counts. Once the settings are where you
want them, click on the 'Generate' button to compute and load the new defect map.

At this point, you'll probably want to examine the results. The main window of PHD2 is still active, so you can take a normal guide exposure to
see how things look. If you want to quickly see the result of using the defect map, just toggle the 'Use Bad-pixel Map' menu item under the 'Darks'
menu. Keep in mind that you don't need to achieve a perfectly smooth, black background in the guider image - you just need to have a sufficiently
small number of remaining hot/cold pixels that neither you nor the PHD2 guiding algorithms will mistake a bad pixel for a star. If you over-correct
with very aggressive settings, you may create so many bad pixel areas that they interfere with detection of usable guide stars. It's easy to make
adjustments with the sliders - just change the slider settings, click on 'Generate' again, and look at the results in the main PHD2 window.

You may find this approach still leaves some hot pixels that you'd like to eliminate. Since the default approach relies on statistics and needs to
apply to a wide range of cameras, it isn't a "fire-and-forget" operation - you will often need to fine-tune it using the steps below.

Step-by-Step Guide to Refining a Bad-pixel Map

The following steps are recommended for refining a bad-pixel map to control pixel-level artifacts in your camera:
1. Cover the guide scope and start looping 5-second exposures
2. Open the Refine Bad-pixel Map window (Menu/Darks/Bad-pixel Map), then drag it to the side of your screen so you can see both the
BPM and guiding windows
3. Adjust the gamma slider in the main window until you can see the hot pixels - this may require a brighter image than you are accustomed to
seeing
4. Select the option "Show defect pixels." With the box checked, red dots will appear for any hot pixels that are already known.
5. Slowly drag the hot-pixels aggressiveness slider left and right until most of the hot pixels are covered by a red dot, with a much smaller
number (or even zero) hot pixels not covered. Click the 'Generate' button
6. Now pick up the remaining hot pixels by manually adding them to the bad-pixel map
Un-check the "Show defect pixels" checkbox
Select a hot pixel in the guiding window by clicking on it
Click on 'Add bad pixel' in the BPM window
Repeat as necessary until you satisfied most of the bad pixels have been handled

18
 Close the BPM window - DO NOT click 'Generate' again because that will undo the manual pixel selection

Once your bad-pixel map has been built, you control its use by the 'Use Bad-pixel Map' item under the 'Darks' menu. This setting is retained
across program executions, so leaving it checked will tell PHD2 to automatically load the defect map and use it for all guide exposures. The
settings for 'Use Dark Library' and 'Use Bad-pixel Map' are mutually exclusive - you can use one or neither, but not both at the same time. As
with the dark library, the bad-pixel map data file is stored permanently, so you can disable its use without losing any data. Both of these data
structures can be used for extended time periods, but it's worth remembering that camera sensors do change over time. As a result, you may want
to rebuild the dark library or bad-pixel maps at periodic intervals or when you start to see a degradation in the appearance of your normal guide
images. In these cases, it is also advisable to click on the checkbox for 'Rebuild Master Dark Frame', which will tell PHD2 to reacquire the
underlying dark frames and recompute a baseline bad-pixel map. You'll then need to refine the map as you did before until you're happy with the
results. There is no reason you should need to interact with either the dark library or bad-pixel map data files, but you can find them located in the
'AppData\Local' logical directory used by your operating system.

Like dark libraries, bad-pixel maps are associated with a particular camera and binning level. PHD2 will check to be sure that the bad-pixel map
matches the camera you are currently using. If it does not, you will see an alert message telling you the bad-pixel map can't be used and must be
rebuilt. This can happen when you've changed cameras or binning factors inside an existing equipment profile, something you shouldn't do unless
you have no need for the old settings.

Reusing Dark Frames and Bad-pixel Maps

If you're using the same camera in multiple profiles, you may want to re-use the dark libraries or bad-pixel maps you built for that camera. This
can be accomplished by importing the camera-related data files into a profile that doesn't already have those files. For example, suppose you built
an original profile - call it Profile1 - that uses your Lodestar guide camera, and you built both a dark library and bad-pixel map for it. Some time
later, you create a new profile, Profile2, that has different mount or focal length properties but still uses the original Lodestar camera. In that case,
you would connect your gear using Profile2, then use the 'Import From Profile...' menu item under the top-level 'Darks' menu. You would select
Profile1 as the source of the import function for the dark library, bad-pixel map, or both. You will be shown only those profiles that have a camera
with compatible sensor geometry (sensor size, pixel size, binning). Clicking on 'Ok' will copy the dark/bad-pixel map files and will associate them
with your new profile, Profile2. Since they are copies, changing the data files in one profile will not affect other profiles. Keeping them
synchronized, if that is what you want to do, will require a subsequent 'import' operation.

19
Visualization Tools
PHD2 provides numerous visualization and display tools to help you see how your guider is performing. All of these tools are accessed under the 'View' pull-down menu and are
described below.
Overlays
Graphical Display
Stats Display
Star Profile and Target Displays
AO Graph
Dockable Windows

Overlays
The simplest display tools are grid overlays superimposed over the main guider display window. These are quite straightforward and include the following choices:
Bullseye target
Fine grid
Coarse grid
RA/Dec - this shows how the telescope axes are aligned relative to the axes of the camera sensor
Spectrograph slit/slit position - for spectroscopy users, this will overlay a spectrograph slit graphic on the main display window. The size, position, and angle of the graphic can
be adjusted to match the optical configuration.
None
You can just click on the various overlay options under the 'View' menu and choose one that suits you.

Graphical Display
The graphical display window is one of the more powerful tools for judging guiding performance, and you will probably learn to rely on it. A typical example is shown below:

The major portion of the window shows the detailed displacements of the guide star for each guide exposure, plotted left-to-right. Normally, one line shows displacements in right
ascension while the second line shows declination displacements. However, you can use the 'Settings' button to the left of the graph to switch to camera (X/Y) axes if you prefer (not
recommended). You can also use the 'Settings' button to switch between display units of arc-seconds vs. camera pixels or to change the colors of the two graph lines. The range of
the vertical axis is controlled by the second button from the top, labelled y:+/-4" in this example. The range of the horizontal axis - the number of guide exposures being plotted - is
controlled by the topmost button, labelled x:50 in this example. This scale also controls the sample size used for calculating the statistics you see in the lower left part of the graph
window. These values show the root-mean-square (RMS or standard deviation) of the motions in each axis along with the total for both axes. These are your best estimators of
guiding performance because they can be directly compared to star sizes and seeing conditions. The 'RA Osc' value shows the odds that the current RA move is in the opposite
direction as the last RA move. This is a carry-over statistic from the original PHD software and its usefulness is limited. If it consistently runs above 0.5, you may be chasing the
seeing because of a Min-Move value that is too low. There are two other checkboxes to the left that can help you evaluate guider performance. Clicking on the 'Corrections' box
results in an overlay showing when guide commands are actually sent to the mount, along with their direction and magnitude. In this example, these are shown as the vertical red and
green lines appearing at irregular intervals along the horizontal axis. This shows you how "busy" the guiding is - under optimal conditions, you should expect to see extended intervals
when no guide commands are sent at all in Declination. The other checkbox, labelled 'Trendlines', will superimpose trend lines in both axes to show if there is a consistent overall drift
in the star position. This is primarily useful for drift aligning where the declination trendline is used extensively. But the RA trendline can show if your mount is tracking systematically
slow or fast (or is seeing the effects of flexure) and can help if you are trying to set up custom tracking rates. The trend line for Dec is also useful if you're trying to choose the correct
direction for uni-directional Dec guiding. If dithering commands are issued, usually by an external imaging application, a 'dithering' label will be superimposed on the graph in the
appropriate time interval. This tells you the star displacements being graphed are being influenced by the dithering operation. The RMS statistics do not include the large excursions
associated with dithering and settling.

The guiding graph will also show the directions (GuideNorth, GuideEast) associated with the guide commands, as shown in the example above. This can be helpful if you are looking
at overall drift and want to determine how to set uni-directional guiding for declination. These directions show how the guide star is drifting away from the lock position. For example,
if the Dec position of the guide star is moving upward in the graph, the guide star appears to be drifting "north" on the camera sensor. This means that south guide pulses will be
needed to move it back to the lock position. Similarly, a downward drift in RA location means the the guide star is moving "east" on the camera sensor and west guide pulses will be
applied. For the purpose of setting up uni-directional Dec guiding, these rules apply:
Dec drifting upward => select Dec guide mode = South
Dec drifting downward => select Dec guide mode = North
For various mount and hardware reasons, these directions may not correspond to actual directions in the sky, particularly for Dec, but that doesn't matter.

The recommended way to look at guiding performance is to use units of arc-seconds rather than pixels. Doing this allows an equipment-independent way of evaluating performance
because it transcends questions of focal length and image scale. To do this, you need to provide PHD2 with sufficient information to determine your guider image scale: namely, the
focal length of the guide scope, the size of the guide camera pixels, and whatever binning level you're using. These parameters are set in the 'Brain' dialog, on the 'Guiding' and
'Camera' tabs, respectively. If they are not specified, PHD2 will use a default image scale of 1 arc-sec/px, and the guiding performance numbers will effectively be reported in units of
pixels. As mentioned in the Basic Use section, the best approach is to use the new-profile-wizard when you create your profile, in which case all these parameters will be set for you.

At the bottom of the graph window are active controls for adjusting guiding parameters "on the fly". The guiding algorithm selections you've made will determine which controls are
shown. These controls have the same effect as those in the 'Brain' dialog, and they eliminate the need to stop guiding and navigate to another window to adjust guiding parameters.
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 Although these controls are prominently displayed, it is generally not productive to change them substantially during on-the-fly efforts to improve guiding. Guiding improvements
normally require long guiding intervals and careful analysis using the PHD2 LogViewer tool - most guiding problems arise from user error or from the mount and the gear attached to it
rather than from the guiding algorithms.

Stats

If you want to monitor guiding performance without necessarily having the graph window open, you can click on the "Stats" menu item. That will display the salient statistics with
controls for clearing the data or changing the number of guide exposures used to compute the statistics. The tracking statistics are the same as those in the Graph tool, and like those,
don't include the effects of dithering and settling. This window is also useful for confirming camera binning, monitoring the guide camera temperature, and getting a quick calculation of
your guide camera's field of view.

Star Profile and Target Displays

The star profile display shows the cross-section of the guide star along with measurements for its full-width-half-maximum (FWHM) and half-flux-diameter (HFD). HFD is generally
a more stable measure of the star size since it doesn't require curve fitting or any assumption about the overall shape of the star image. That's why automated focusing applications like
FocusMax use it. If you see substantial fluctuations in this parameter or wildly varying star profiles, it may be an indication that the star is too faint, the exposure time is too short, or
the camera is out-of-focus. This tool can help with focusing the guide camera, a procedure that can be a bit tedious if you're using an off-axis-guider at a fairly long focal length. For
that purpose, the HFD number is shown in a large font so you can see it from a distance while focusing your guide scope/camera. Just un-dock the Star Profile window and expand it
until you can see the HFD number easily. If you are starting well out-of-focus, you'll probably see only a few fuzzy stars in the frame, so just choose the smallest one that is clearly
visible. Use exposure times of at least 2 seconds if possible so you don't chase the seeing. At the same time, don't let the star become saturated, showing a distinctive flat top. Now
adjust the focus so the HFD gets consistently smaller - but stop as soon as HFD reverses direction or seems to plateau. At that point, the star may be saturated, so move to a dimmer
star in the field. Since you have already improved the focus, you can hopefully see a dimmer star. Continue in this way until you've reached a focus point that shows a minimum level
of HFD for the faintest star you can use. At each point in the focusing process, you'll probably want to watch the HFD values for a few frames so you can mentally average out the
effects of seeing. Bad focus is a common issue for beginners, leading to problems in calibration or generally poor guiding results. Use the Star Profile tool to be sure the star doesn't
have a flat top (saturation) and shows a tapered shape like the example shown above.

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The target display is another useful way to visualize overall guider performance. The red 'X' shows the star displacement for the most recent guide exposure, while the blue dots show
the recent history. You can zoom in or out with the controls at the upper left of the window, as well as change the number of points shown in the history. If you are using an
ASCOM connection for either the 'mount' or 'aux-mount', PHD2 will also show the directions (SkyNorth, SkyEast) associated with the star movement, as shown in the example
above. This can be helpful if you are looking at overall drift and want to determine how to set uni-directional guiding for declination. The up/down convention used in this graph has
nothing to do with the camera orientation or N-S-E-W movements in the field of view.

Adaptive Optics (AO) Graph

The AO graph is equivalent to the 'target' display, but shows the history of corrections relative to the axes of the adaptive optics device. The red rectangle indicates the outer edges of
the AO device, while the interior yellow rectangle shows the "bump" region. If the star moves outside the yellow rectangle, PHD2 will send a sequence of move commands to the
mount - the "bump" - to smoothly place the guide star back near the center position. When this occurs, green and blue lines will show the incremental bump and the remaining bump
respectively. The white dot on the display shows the current AO position, and the green circle (red when a bump is in progress) shows the averaged AO position. The button in the
upper left controls how many points will be plotted in the history.

Dockable/Moveable Graphical Windows

When the various performance windows are initially displayed, they are "docked" in the main window. This means they are sized in a particular way and are aligned with two edges of
the window - they are entirely contained within the bounds of the main PHD2 window. However, you can move them around and resize them by clicking and dragging on the title bar
of the window you want to examine. This will often let you get a better view of the details being shown in the graphs. They can be re-docked by dragging the title bar to the general
region in which you want them docked - bottom, right, etc. With just a bit of practice, it's easy to place them where they are most convenient.

There is also a menu item under the 'View" pulldown menu labeled 'Restore window positions.' Clicking on this menu item will automatically restore all of the dockable/moveable
windows to their default, docked positions. This can be useful , for example, if you are switching between screens with different resolutions and one or more of the dockable
windows has been "lost." This function also restores the main PHD2 window to its default size, with a position near the upper lefthand corner of the screen.

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Advanced Settings
Advanced settings are accessed by clicking on the 'Brain button' in the main display. PHD2 has a large set of parameters that can be adjusted to
optimize your guiding performance. Although these are called "advanced" settings, they are not particularly difficult to understand, and you
shouldn't hesitate to explore them. All of the fields on these forms include "tool tips", small message windows that describe each field in some
detail. Simply "hover" the cursor over the field to see the tool-tip. In many cases, this will provide all the information you need. Because there
are so many parameters available, the Advanced Dialog in PHD2 is organized into notebook tabs that are activated by clicking on the tab names.
All of the tabs share a common set of 'Ok' and 'Cancel' buttons at the bottom of the form. Clicking on 'Ok' means that changes made to any of
the tab fields will be put into effect. Clicking on 'Cancel' discards any changes that were made.

Global Tab
Camera Tab
Guiding Tab
Algorithms Tab
Other Devices Tab

Global Tab

The controls on the 'Global' tab are well-described by their respective tool-tips, but they are summarized here for completeness:
'Language' - determines the language used in the PHD2 user interface, subject to available localization. Changing this requires a program
restart
'Reset Configuration' - restores all settings to their initial values as if PHD2 had been freshly installed
'Reset Don't Show Again messages' - restores the display of alert messages if you have previously chosen to not show them
Software Update
Automatically check for updates - allow PHD2 to check for software updates when the program starts up. If no internet connection
is available, checking will be deferred until the next time PHD2 is run.
Only check for major releases - indicates whether to include development builds when checking for software updates.
See the Software Update section for more information about PHD2 software updates.
'Log File Location' - specifies a directory where PHD2 guide logs, debug logs, and any diagnostic image files will be stored. The default
location on Windows is the "My Documents" folder associated with the logged-in user..
Dither Settings
'Random mode' - tells PHD2 to use a random-number generator to compute both the size and the direction of the dither, subject to
any constraints imposed by RA-only mode or by the Dec guiding mode being set to 'Off'.
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 'Spiral mode' - tells PHD2 to dither with fixed-size amounts in a clockwise spiral pattern. This can be a good choice when the
imaging camera has significant fixed-pattern noise or the mount has a troublesome amount of Dec backlash.
'Dither RA only' - tells PHD2 to dither only on the RA axis.
'Dither scale' - an optional multiplier used to adjust the maximum-dither amount specified by the image application. See Dithering
Operations
'Enable diagnostic image logging' - used primarily for product support and diagnosis of problems dealing with the guide camera or PHD2
star-recognition and measurement. Guide frame images are captured and logged in a FITs format subject to the filter/trigger controls in the
group-box. Images are saved in sub-folders of the PHD2 logging directory with the date and time encoded as part of the sub-folder name.
Individual guide frames are saved with filenames that indicate the time the image was captured and the reason the frame was saved. Since
the guide frames are saved in a FITs format, the header will include other useful information such as exposure time. Because the logging
function is primarily used for trouble-shooting, the image sub-folders are automatically removed after 30 days. If you wish to keep the
images for your own purposes, you should either rename the sub-folders or copy/move them to a different directory. When logging is
triggered by one of the "events" - e.g. lost star or large errors - a group of images (an image set) will be saved, centered in time on the
image that triggered the event. This provides a record of guider images that will show what the guide star and guide frame looked like both
before and after the unusual condition occurred. The various triggering and filtering controls are described below and are also shown in the
tooltips for the controls:
'All lost star frames' - logs the image set for any lost-star events, regardless of the reason for the lost star (low SNR, mass-change,
etc.)
'All auto-select star frames' - logs the image set for any frames used for auto-selection of the star, regardless of outcome. Note that
any failed attempts to auto-select a star will always result in a logged image, regardless of choices made in the user interface.
'When relative error exceeds' - logs the image set when the star deflection on the current frame exceeds the running-average error by
the factor chosen in the adjacent spin control. For example, if the average (RMS) error is 0.5 pixels and the current frame's error is
1.5 pixels, the relative error is 3.
'When absolute error exceeds' - logs the image set when the star deflection exceeds the number of pixels specified in the adjacent
spin control.
'Until this count is reached' - logs images until the count matches the value of the adjacent spin control. The counter is reset to zero
when the limit is reached.
Since the images are saved in an industry-standard format, there are many astronomy-related applications that can display or analyze them,
many of which are free. Most of the image-capture and image-processing applications can do that along with other, more specific tools that
can perform detailed measurements on the stars and the optical quality of the field of view. You can just do a web search to find a list of
applications that support the FITs format for whatever platform you're using. If you simply want to look at the images to check focus or see
the general quality of the images being returned from your camera, you can use PHD2 for that. With PHD2 in an idle state - neither looping
nor guiding - just drag-and-drop one of your saved FITs image onto the main window. The display will then update to show the image you
just dropped. There's no need for PHD2 to be connected to any of the hardware. You can adjust the gamma slider, select a star (manually
or automatically), and use the Star Profile tool to view the HFD and profile of the selected star.

Camera Tab

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The controls on the 'Camera' tab are used as follows:
'Noise reduction' - specifies the algorithm to use for handling noisy guide camera images - those for which dark frames are not sufficient.
Choices include None, 2x2 mean, and 3x3 median. Both 2x2 mean and 3x3 median will reduce the noise considerably. 3x3 median is
especially effective at removing hot pixels and neither will significantly affect guiding accuracy. However, creating a bad-pixel map is likely
to be a better solution with less impact on your ability to detect faint stars.
'Time lapse' - imposes a fixed delay between guide exposures. This can be useful if the guide exposures are very short and you don't want
to overload either the mount or the camera link with very high traffic rates.
'Auto Exposure' - these are the settings that control Auto exposure time.
Min Exposure - the minimum exposure time - PHD2 will not set the exposure time less than this value, even if the guide star SNR is
higher than the target SNR value. If the min exposure time is set too low, you are likely to chase seeing effects and thereby get poor
guiding results. Users of AO units might set this to a lower value since rapid small corrections are more manageable with an AO.
Max Exposure - the maximum exposure time. Before a guide star is selected, PHD2 will set the exposure time to the maximum value.
Once a guide star is selected, PHD2 will then incrementally decrease the exposure time until the desired SNR is reached.
Target SNR - this is the average SNR value that PHD2 will attempt to achieve by adjusting the exposure time. SNR can fluctuate
from frame to frame even with a fixed exposure duration, so be sure to account for that when choosing a target SNR value. PHD2
will reject frames when SNR drops below 3.0. The default value of 6.0 should provide enough of a cushion to prevent fluctuations
from causing the SNR to go below 3.0 but a higher value is desirable. As mentioned in the 'Basic Use' section, SNR is similar but
not identical to the signal-to-noise ratio used in photometry.
'Star Saturation Detection' - when identifying candidate guide stars, PHD2 tries to avoid saturated stars in order to get the most accurate
calculations of their positions. You can assist this process by specifying how the assessment of saturation should be done:
Saturation by ADU value - this is the preferred option because it relies on the brightness levels measured by the guide camera sensor.
Most guide camera drivers return image data in either 8-bit or 16-bit formats even if the camera electronics natively work in 12-bit
or 14-bit modes. An 8-bit camera will saturate at a brightness level of 255 while a 16-bit camera will saturate at levels above 65000.
If you are uncertain about your camera's behavior, you can use the Star Profile tool to measure the brightest pixel level when taking
exposures of a very bright star.
Saturation via star-profile - this relies on a less accurate judgment of saturation based on whether the star profile has a flat top. It is
not recommended for normal applications.
'Pixel size' - The guide camera pixel size in microns. This is the second of two parameters needed by PHD2 to compute the guider image
scale and thus report guider statistics in units of arc-seconds. The other parameter required for this is the guide scope focal length, located
on the 'Guiding' tab. Refer to your camera documentation to determine the correct value for pixel size. If your camera has non-square
pixels, just choose one of the dimensions or input the average of the two. The pixel size has no effect on guiding accuracy, so a small
amount of imprecision in the user interface won't cause any problems. If you're using the binning setting in this dialog to control camera
binning, the pixel size should be the native, un-binned size. Note: this control may be disabled if the camera and camera driver can report
the pixel size to PHD2. In that case, the value displayed in the disabled control represents the device-reported pixel size - it is what it is. If
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 you're also specifying a binning factor at the camera driver level rather than in PHD2, the reported pixel size may change as a result. It is
generally better to use PHD2 to set binning (see below).
'Camera gain' - Sets the gain level for the many cameras that support this feature. Reducing this parameter can help to reduce the noise
level or may allow use of a bright star without saturation. The range of values and their specific effects are dependent on the individual
camera, so this PHD2 parameter is treated as a percentage of the range between the minimum and maximum gain values supported by the
camera. For example, if the camera uses absolute gain values in the range of 40 to 80, a PHD2 gain value of 50% would translate to a
camera gain of 60.
'Disconnect nonresponsive camera after (seconds) - Camera malfunctions will sometimes occur, often because of faulty USB connections.
In many cases, the camera will not return the requested image data, and PHD2 will appear to "hang." This parameter determines how long
PHD2 should wait for a response after the expected exposure time has expired. For example, a timeout value of 5 seconds in conjunction
with an exposure time of 2 seconds will tell PHD2 to wait up to 7 seconds for a response. If the data are not received within that period,
PHD2 will attempt to halt the operation, disconnect the camera, and display an alert message in the main window. Since a hardware
problem is likely the underlying issue, this recovery attempt won't always succeed. You should be generous with these timeout values to
avoid spurious recovery actions. Also, if you are using a guide camera that shares electronics with the main imaging camera, you should set
this timeout to a large value, well above the maximum expected time for a full-frame download from the main imager. This is a consideration
for users of the SBIG driver that is packaged with Sequence Generator Pro. Regardless of whether PHD2 is able to handle the situation
gracefully, the underlying problem is almost certainly in the hardware or the camera driver and will need to be resolved before guiding is
continued.
Binning - for those cameras that support on-chip (hardware) binning, you can specify the binning that will be used while taking guide
exposures. See below for a more detailed discussion. This control will appear only if the camera is capable of on-chip binning and only if
the camera is connected to PHD2.
'Use subframes' - For cameras that support this feature, PHD2 will download only a subframe of each guide exposure. This is very useful
for cameras with slow download times, allowing them to be used more effectively for guiding. This feature applies to both calibration and
guiding. During initial looping without a selected star, the full frame is downloaded, but once a star is selected, only this small subframe is
downloaded. If you are using subframes but want to see the full frame to select a different star, just shift-click anywhere in the image
display window or shift-click on the 'Auto-select star' button.
Cooler controls - a few guide cameras support sensor cooling. These controls let you specify whether the cooler is on and what the cooler
set-point should be.
Use of Binning
Some of the guide cameras available in PHD2 support hardware-level binning, and this may be helpful in situations where you are guiding at long
focal lengths or have a guide camera with very small pixels. These scenarios often result in having to use faint guide stars, and the guider images
may be substantially over-sampled. Over-sampling provides no real benefit, and the projection of a faint star disk onto many small pixels can
result in a low signal-to-noise ratio (SNR). By binning the image, you can reduce the impact of camera read noise and thus improve the SNR; and
if you are over-sampled, you won't degrade the accuracy of computing the guide star location. Choosing a binning factor greater than one will
have the following effects:
1. Star images will have a higher SNR and will be easier to detect above the background noise level. This is especially helpful if you are limited
to using faint stars (i.e. with SNR values below about 10).
2. The amount of data downloaded from the camera will be reduced by the square of the binning factor. This can be helpful if you are using a
camera that makes heavy use of USB resources even if star brightness and SNR are already reasonable with un-binned images. Of course,
using sub-frames can achieve the same result once a star has been selected.
3. The resolution (image scale) of your guider image will be reduced by the binning factor. This is not likely to be a problem if the un-binned
image scale is below 1 arc-sec/pixel, but your guiding results may suffer if the un-binned image scale is above 3 arc-sec/pixel. You may
need to experiment because the results will also depend on the image scale of your main camera system.
Each binning level requires its own dark frames and bad-pixel map - they are not interchangeable, nor can a transform be done automatically. If
you want the flexibility of switching back and forth between binning settings, you should create separate profiles for each binning value. Then
build a dark library and a bad-pixel map for each of those profiles. When you want to change binning factors, just switch to the profile that has the
setting you want, and a dark library and/or bad-pixel map will be available. If you want to check that the camera is binning correctly, you can use
the Stats window to confirm the frame size and current on-camera bin settings.

Guiding Tab

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The guiding tab shows the parameters used for calibration, star-tracking, and guiding behavior shared by all of the guide algorithms..

Guide Star Tracking

'Search region' - specifies the size of the "tracking rectangle", in units of pixels. You may need to increase this value if your mount does not
perform well or, more commonly, if it's not well-aligned on the celestial pole. You may also want to increase it temporarily while using the
Guiding Assistant so that backlash measurement can be done without losing the guide star. Just remember that an overly large search region
also increases the likelihood that multiple stars will live within its boundaries, which could lead to guiding problems.
'Star mass detection' - tells PHD2 to monitor the brightness and size of the guide star compared to the sky background. You may need to
disable this feature or set the tolerance to a higher number if you're using a fine image scale and are getting too many lost-star events
because of this feature.
'Star mass tolerance' - if the 'Enable' box is checked, PHD2 will trigger a 'lost star' error if the measured brightness and size vary by more
than this percentage. This might be useful if you have two stars inside the tracking rectangle and you want to be sure PHD2 doesn't
mistakenly switch stars. It can also prevent errors caused by thin clouds, high camera noise, or alpha particle artifacts; but it may be
unreliable if you are guiding on a faint star. If you are getting too many 'lost star' errors when the star is plainly visible on the display, try
increasing the value of this setting. Resetting the 'Enable' checkbox or setting the threshold to 100 will disable the warnings entirely.
'Minimum star HFD' - specifies the minimum half-flux-diameter (roughly the 'size') of a suitable guide star. This is probably the best way to
prevent PHD2 from mis-identifying clumps of hot pixels as usable guide stars. You can determine a suitable value for your system by
manually selecting some small stars that you know are not just hot pixels, then use the star-profile tool to see the HFD values of those stars.
You'll want to specify a minimum HFD value that allows selection of legitimate faint stars but not hot pixels. If you encounter situations
where PHD2 is trying to guide on a hot pixel, be sure to set this parameter.
'Minimum star SNR for AutoFind': specifies the minimum SNR value that will be accepted by the auto-select function for non-saturated
stars. This should only be adjusted by experts because a value that is too large can result in no stars being selected. It can be used in
situations where you would rather use a saturated star instead of a faint star that you know from experience will prove to be unusable.
However, many of these situations can be avoided by getting better guide camera focus, refreshing the dark library, or slightly increasing the
exposure times.
'Use multiple stars' - determines whether PHD2 will use more than one star for guiding. See Multi-star Guiding for details.
'Auto-selection frame downsample' - can be used in unusual situations where PHD2 guide star auto-selection is not recognizing misshapen
stars. If this happens, you can try values greater than 1 to improve the chances of recognizing such stars. For most users, this property
should be left at its default value of 'Auto'.
'Beep on lost star' - specifies whether PHD2 should produce an audible 'beep' sound when the guide star is lost during guiding.
Calibration
'Focal length' - the focal length of the guide scope (millimeters). This provides one of two parameters needed by PHD2 to compute the
image scale and thus report guiding performance in units of arc-seconds. The other parameter required for this is the guide camera pixel
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 size, located on the 'Camera' tab. If these two parameters aren't set properly, some of the default guiding parameters may not be set
correctly, and we will be handicapped in trying to assess your guiding performance and help you resolve problems. If you use the new-
profile-wizard, these values will probably be correct.
'Calibration step-size' - specifies the duration of the guide pulse that PHD2 will use during calibration. Its use is described in the 'Auto
Calibration' section of the 'Basic Use' help page. You can adjust the value depending on whether the guide star is moving too quickly or too
slowly during calibration. As a general guideline, it is good to calibrate within about 30 degrees of the celestial equator (declination = 0),
and to use a calibration step size that will result in 8-14 steps in each direction. The 'Advanced...' button to the right of this control will
launch a calculator dialog that can help you compute an appropriate value (see below)
'Auto restore calibration' - tells PHD2 to automatically reload the most recent calibration data as soon as the equipment is connected. If
you're using an ASCOM (or Indi) mount connection or have an 'aux-mount' connection, you may want to set this option. Conversely, if
PHD2 has no scope pointing information available, this option will normally be reset. The new-profile wizard will ask you how you want to
set this option. Note that auto-restore is remembered for each separate equipment profile, and it only has an effect when you load the
profile and connect to the equipment. If you want to force a recalibration before an individual guiding session begins, you can simply clear
the mount calibration (see below). If you have set the auto-restore option, you must be sure that the guide camera is not rotated with
respect to the guide scope or the sky.
'Assume Dec orthogonal to RA' - Normally, the calibration process independently computes the camera angles for both right ascension and
declination. There is no need for great precision on these values, and the default behavior normally works well. However, if your mount has
very high periodic error or you are dealing with very bad seeing conditions, you may want to force the RA and Declination angles to be
perpendicular. If you choose that option, PHD2 will compute the camera angle for RA, then assert a declination angle that is orthogonal to
it.
'Clear mount calibration' - tells PHD2 you want to clear the calibration data currently being used for the mount and re-calibrate before
guiding is restarted. You might do this for a variety of reasons - rotating the guide camera or changing the mount guide speed, for example.
You can also accomplish the same result by doing a Shift-Click on the PHD2/guiding icon on the main page, which will force a re-
calibration.
'Use Declination Compensation' - if PHD2 can get pointing information from the mount via an ASCOM connection ('Mount' or 'Aux'), it will
automatically adjust the RA guide rate based on the current declination. This box should normally be left checked except in unusual cases.
For example, SiTech mount controllers may apply a compensation automatically, in which case the box should be left un-checked. Don't
confuse this option with 'Declination backlash compensation', which is an entirely different feature.
Shared Guiding Parameters
'Fast re-center after calibration or dither' - during calibration or dithering, the mount may be moved a significant distance from the initial
"lock" position. If you click this checkbox, PHD2 will move the mount back to the lock position as quickly as possible, using the largest
guide commands permitted by the 'Max Duration' settings of your guide algorithms and by the size of your tracking region. This is only an
optimization, so the use of this checkbox is completely optional. If you find that calibration often fails because the star is lost during the fast
re-center, you should disable this option. That sort of problem may indicate that you have a large polar alignment error or excessive
periodic error in RA. You can run the Guiding Assistant to help see what's causing the problem.
'Reverse Dec output after meridian flip' - tells PHD2 how to adjust the calibration data after a meridian flip. Some newer mounts track
their 'side of pier' state and automatically reverse the direction of the declination motor. Older mounts do not do this. In either case, PHD2
needs to know if the mount will automatically change its behavior based on side-of-pier. You may have difficulty finding information about
how your mount behaves in this respect, so PHD2 provides the Meridian flip calibration tool to determine the correct setting automatically.
It's also easy to figure out the setting manually with this quick experiment:
With the checkbox disabled, calibrate on one side of the pier, then move the mount to the other side.
If you are guiding via ASCOM or Indi or are using an 'aux mount' connection, just start guiding.
If you're guiding only via ST-4 and PHD2 has no scope pointing information, first select 'Flip Calibration' under the 'Tools' menu, and
then start guiding.
In either case, if the guiding works normally, leave the box un-checked; but
if you see guiding run-away in declination, check the box and repeat the entire procedure, including calibration.
'Enable mount guide output' - this is normally checked because it tells PHD2 to send guide commands to the mount. But there are some
circumstances where you might want to disable this, usually because you want to observe the uncorrected behavior of the mount. For
example, you can disable guider output in order to see the general shape and amplitude of your mount's periodic error or to check the
amount of drift from polar mis-alignment. In most cases, you will be better off running the Guiding Assistant for these purposes, which
automatically handles this setting for you.
'Stop guiding when mount slews' - a diagnostic option for working with ASCOM mount drivers that may report the slewing status
incorrectly. The option should be left checked unless you know the driver for your mount has this problem (highly unlikely). Also, it will
generally not detect slews that are initiated by the hand-controller. In any case, PHD2 will continue to try to track the guide star, so slews
will typically result in lost-star notifications - beeping and flashing of the PHD2 image window.
Advanced Calibration Calculator

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To review or change calibration parameters, be sure the topmost four edit controls are correctly filled in. If you have already specified the focal
length and the camera pixel size in the 'Guiding' and 'Camera' tabs respectively (or via the new-profile-wizard), those fields will already be
populated in this form. If you are using an ASCOM connection to your mount, the fields for "Guide speed" and "Calibration declination" will
usually show the correct values unless the driver doesn't report them correctly. Otherwise, you'll need to supply them yourself. The guide speed is
specified as a multiple of sidereal speed - most mounts will use something like 1X or 0.5X sidereal, but you can choose something else. Note:
changing the guide speed setting here never changes the guide speed setting in the mount - that can only be done via the mount
driver or the hand-controller. If this field is already filled in, changing it will have no useful effect. You can leave the 'calibration steps'
field at the default value of 12, which is likely to result in a good calibration. Use of a significantly smaller value raises the likelihood that seeing
errors or small mount errors will cause calibration errors . You can also change the total calibration distance if you have some reason to think the
default value of 25px is inadequate. You should be careful with this because "bigger" is not always "better". With larger required calibration
distances, the calibration is more likely to be affected by large uncorrected periodic error in RA or large drift in Dec. As you change the values in
these fields, PHD2 will recalculate your current image scale and a recommended value for the calibration step-size. If you then click on 'Ok', that
value will be inserted into the calibration step-size field of the 'Guiding' dialog. Clicking 'Ok' will also populate the focal length and camera pixel
size fields in the 'Guiding' and 'Camera' tabs, so any changes you made in the calculator will be reflected there as well. However, this will not be
done if you click on 'Cancel' in the calculator dialog. Again, PHD2 never changes the guide speed setting in your mount regardless of what may be
entered in the 'Guide Speed' field.

The goal of the calculator is to recommend a step-size that is likely to result in an accurate calibration without wasting too much time, and the
automatically computed values will usually work well. As long as you are getting successful calibrations without alert messages, the calibration
parameters should be left alone. If you've used the new-profile-wizard to build your equipment profile, there's rarely any reason to use the
'Advanced" button and the Calibration Calculator dialog.

Algorithms Tab

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The algorithms tab can be used to select the guiding algorithms you want to use and to fine-tune the parameters associated with them. The
parameters displayed will change significantly if you change the algorithm selections. For that reason, all the parameters related to guide algorithms
will be treated together, in a separate section.

The remaining controls, the ones that are independent of the guiding algorithm selections, are described below.
'Max RA duration' - specifies the maximum allowed guide pulse duration for right ascension. You might reduce this below the default value
if you want to avoid chasing a large deflection that could be caused by a spurious event (e.g. wind gust, hot pixel, etc.) .' However, there is
rarely a good reason for changing it if you have protected yourself against hot pixels (Minimum star HFD).
'Use backlash comp' - this controls whether PHD2 will apply a compensation factor when the direction of declination guiding needs to be
reversed. See section below.
'Max Dec. duration' - specifies the maximum allowed guide pulse duration for declination (same as above but for declination).
'Declination guide mode' - gives you additional control over declination guiding. Declination guiding is not like RA guiding because the
errors are not caused by imperfections in your mount's gears. Instead, deflections in declination are primarily the result of imperfect polar
alignment or flexure. The result is an error that should be smooth and mostly uni-directional, assuming there is no over-shoot from an earlier
correction. The default value of 'auto' tells PHD2 that some reversals in direction are acceptable, subject to the behavior of the various
guiding algorithms. However, if your mount has severe declination backlash, you may want to prevent direction reversal altogether. You
could then select either 'north' or 'south' to restrict corrections to only that direction (uni-directional Dec guiding). Keep in mind, however,
that an over-shoot in correction with one of these modes might leave the star positioned off-target for an extended period of time. So you'll
probably want to use conservative parameters for aggressiveness if you are disallowing direction reversals. Finally, a choice of 'off'' here
disables declination guiding altogether, an appropriate choice for simple tracking mounts that don't support Dec guiding.
'Reset' - resets the guiding parameters for the selected RA or Dec algorithm to their default values. Min-move settings will be set using the
same algorithm employed in the new-profile-wizard. If you previously used the Guiding Assistant to adjust the min-move settings, you
should probably repeat that procedure.

Declination Backlash Compensation

Most commonly-used mounts have some amount of backlash in declination. This causes a delay whenever there is a change in direction of the
Dec guide commands. During this interval, the declination gears aren't fully engaged and the axis doesn't move in response to the guide commands.
Many mounts have settings for backlash compensation but these should not be used for guiding - they are typically intended for visual use only.
Because the actual amount of compensation needed at any given time may depend on the pointing position and the mechanical load on the system,
a fixed value will usually result in oscillations that never stabilize. The backlash compensation implemented by PHD2 is adaptive, meaning that the
compensation amount is adjusted up or down depending on the measured results. Before enabling this feature, you should run the Guiding

30
Assistant and measure the declination backlash - the time delay required to fully reverse direction in declination. Keep in mind, the higher the guide
speed setting in the mount (e.g. 0.9x sidereal), the smaller this delay will be. If the measured amount is 3 seconds or less, the Guiding Assistant will
recommend trying backlash compensation. If you apply that recommendation, the backlash compensation settings will be handled for you
automatically. The UI controls for backlash compensation include settings for 'minimum' and 'maximum' compensation amounts. These effectively
limit the range of the adjustments that are made to the starting compensation value. If you're experienced with your mount's behavior, you can
adjust these settings manually to be sure that the compensation stays within a range that you know works well. Otherwise, you should just leave
these at their default values. The backlash compensation algorithm will generally work well if the backlash is less than a few seconds and the
mount doesn't have other significant mechanical problems. You should expect a short period of instability when guiding starts because the initial
state of the Dec gear system is unknown - just let it stabilize before you actually start imaging. If you see recurring periods of Dec oscillation or the
axis won't settle down, disable the compensation feature and submit your debug log file to the PHD2 support forum. It's important to note that the
correct amount of Dec backlash compensation will often change depending on the scope pointing position. This can be caused by uneven gear
wear on the Dec axis or by differences in the gravitational load being applied to the axis.

Uni-directional Declination Guiding

As discussed elsewhere, some mounts have too much declination backlash to support guiding in both north and south directions. This situation can
be mitigated by configuring PHD2 to guide in only one of the directions, what we call uni-directional Dec guiding. This can be a manageable
situation because declination guiding is only intended to correct for slow drift - errors caused by polar misalignment and to a lesser extent,
mechanical flexure. Ironically, you might want to de-tune your polar alignment a bit to make it easier to see the drift direction and to reduce the
likelihood that seeing will interfere with uni-directional guiding. Remember that polar mis-alignment, within reason, doesn't usually degrade guiding
performance. Instead, it may introduce field rotation if you're imaging near the pole and have a large camera sensor. A good first step would be to
polar align to within 5-10 arc-min of the pole before setting up for uni-directional guiding. You can always go back later and check for field
rotation. Just take a sample image with your main camera at the highest declination you would expect for imaging - perhaps 70 degrees north. If
you don't see field rotation there, you can leave the polar alignment where it is. With any amount of polar mis-alignment, the direction of Dec
corrections will change at some point in the sky. (Technically, it will reverse directions at two points in the sky but one of those is usually below the
horizon.) The sky location for the reversal depends entirely on how you are mis-aligned on the pole - the relative amounts of azimuth and altitude
alignment errors. You may even have a situation where the reversal point is near enough to the horizon that you don't encounter it during normal
imaging.

To set up for uni-directional guiding, you can follow these steps:

1. Move to a field with a good guide star and run the Guiding Assistant for several minutes. Look at the guiding graph and note whether the
guide star is drifting north or south. Once you see this, reset the Dec guide mode to issue corrections in the appropriate direction. For
example, if the star is drifting north, set the Guide mode to 'south.'
2. Try using the 'LowPass2' guiding algorithm for declination and start with a fairly low aggressiveness factor, say 50%. If the aggressiveness is
too high, the correction may push the star to the "wrong" side of the lock position, where it will remain until the slow drift rate moves it back.
It's better to issue a few consecutive small corrections rather than one larger one in order to minimize this type of over-shoot.
3. Watch the guiding graph to be sure the corrections are being issued in the right direction and the star isn't just steadily drifting off-target.
Over the course of minutes or hours, you may notice the amount of drift is decreasing. This means you are slowly approaching the point of
declination reversal and you should be prepared to change the Dec guide mode accordingly.
4. If you are dithering, you may want to set the dithering parameters to "RA-only" to avoid disrupting the Dec guiding.

Other Devices Tab

If you are using either an adaptive optics or rotator device, the "Other Devices" tab will be shown. The upper section deals with the AO device if
one is being used. You can use these parameters to control the calibration process and the manner in which 'bump' operations are done. The
'calibration step' field tells PHD2 the amount to move the tip/tilt element in each of the up/down/left/right directions, in units of AO steps, during

31
calibration. The guide star position is measured at the beginning and end of each leg of the calibration, and the 'samples to average' parameter tells
PHD2 how many samples to take at each of these points. Averaging images is important because the seeing will always cause the guide star to
"bounce around" a bit. As discussed elsewhere, the AO unit can make corrections only within a limited range of guide star movement. You
will want to initiate mount 'bump' corrections before these limits are actually reached, and the 'bump percentage' field is used for that purpose. To
move the mount, the full bump correction is accomplished in steps - the 'bump step' field controls the size of these increments. If the bump
operation has begun and the guide star remains outside the "bump percentage" area, PHD2 will increase the bump size until the guide star is back
within that range. Additional movement from that point to the center position will continue at the specified "bump step size". This complexity is
required in order to maintain good guiding, with no elongated stars, even as the mount is being bumped. During the bump operation, the AO is
continuing to make corrections, so the long "mount bump" is continuously offset by adjustments in the AO. The 'AO Travel' field specifies the
number of steps the AO can make on each axis. The default value works well for most SX AO devices but in some cases it may be too large. If
you encounter problems during AO calibration where the AO hits its limits, you can adjust the 'AO Travel' amount downward.

The 'Bump on dither' option tells PHD2 to bump the mount when a dither command is received and thus move the guide star back closer to the
center position of the AO. The option to enable or disable AO guide commands operates independently from the 'Enable mount guide output'
checkbox in the Guiding tab. So you can independently enable/disable either the guide commands to the tip/tilt device or the 'bump' guide
commands to the mount. The same principle holds for the 'Clear AO calibration' option - that will force a recalibration of the AO without affecting
calibration of the mount. The 'Mount Backlash Compensation' controls let you apply PHD2 Dec backlash compensation when mount bumps are
done. This can help speed up large dither operations, but it's only appropriate if the mount has a limited amount of Dec backlash. You should use
the Guiding Assistant to measure your Dec backlash and see what it recommends with regard to using Dec backlash compensation.

When an AO is in use, the 'Algorithms' tab will only show choices for controlling the tip/tilt optical element in the AO device itself.

Since the AO is not trying to move a heavy piece of equipment, you can afford to be more aggressive in your guide algorithm choices. The default
algorithms for an AO are 'Hysteresis'', which gives you an easy way to control damping and aggressiveness. If you use a different algorithm, you
should probably start with a high level of aggressiveness there as well. The other, shared guiding parameters normally displayed on the
'Algorithms' tab will not be shown for the AO because they aren't used to control the device.

The rotator device has only one parameter, which lets you match the behavior of the device to the ASCOM notion of positive and negative angles.
The "Reversed" checkbox can be used for optical systems that reverse the image, usually because they have an odd number of mirrors. The
direction and amount of rotation is used to adjust the calibration data, so PHD2 follows the ASCOM standard: "the rotator position is expressed
as an angle from 0 up to but not including 360 degrees, counter-clockwise against the sky." Experimentation is likely to be the quickest way to
determine if the box should be checked.

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Guide Algorithms
Guiding Theory
Guide Algorithm Parameters

Guiding Theory
The default guiding algorithms in PHD2 are well-established and should work well for most users. Unless you already have some experience with
guiding and understand the basics, you should be somewhat cautious about changing algorithms. However, you may have some special
circumstances that require changes or you may simply want to experiment with the different algorithm choices. The Advanced Settings dialog in
PHD2 makes it easy to do that. Each algorithm has a set of parameters that controls how observed changes in guide star position (star
deflections) are translated into guiding commands that are most likely to restore the star to its initial position.

Before discussing the details of these parameters, it is worth reviewing a little guiding theory and looking at what these algorithms are trying to
accomplish. Setting aside adaptive optics devices, which are considerably different, conventional guiding faces enormous challenges. The problem
at hand is how to move machinery that weighs tens or even hundreds of pounds with a level of precision that will not cause streaked or oblong
stars. Even though many guide cameras can record guide star deflections of only a few microns on the sensor (e.g. 0.0002 inches, 0.005
millimeters), we still expect the mount and the guiding software to move the camera across the sky for hours with this level of precision. Guiding
applications like PHD2 are best able to deal with tracking errors that are "slow and steady", not "fast and random." Sources of slow and steady
(correctable) errors include the following:
Certain kinds of mechanical imperfections in right ascension gears, including those that cause periodic error.
Small errors in the sidereal tracking rate of the mount
Atmospheric refraction - stars appear to move more slowly as they near the horizon
Limited kinds of mechanical deflection and flexure - but not differential flexure
Mis-alignment of the right ascension axis on the celestial pole
So what isn't included in the above and isn't correctable by conventional guiding? Unfortunately, it's a very long list, of which a few are:
Atmospheric seeing ("turbulence")
Gear noise, roughness, and vibration
Differential flexure - relative movement between the imaging scope and the guide scope
Wind gusts, cable snags, grit in the drive gears
And lots more...
The common denominator shared by the guide algorithms is the need to somehow react to the slow and steady deflections while ignoring the rest.
This is a difficult problem at best because any given guide star deflection is likely to have contributions from many of these sources. And if that
isn't hard enough, remember that real-world mounts are never perfect - so the move you ask for will not be exactly the move you get. Usually, the
most important requirement for any algorithm is to avoid over-correcting, wherein the mount is being pushed back and forth and the guiding never
stabilizes. A typical approach in these algorithms is to ignore deflections that are most likely caused by seeing and to apply "inertia" or "impedance"
to the guiding corrections that are sent to the mount. That means making corrections that follow a pattern and are generally consistent with
corrections that have been made before, while being reluctant to make corrections that require a big change in direction or amplitude. Resistance
to changes in direction is particularly important in declination, where gear backlash is a common problem. Hopefully, this background will give you
enough insight into the basics of guiding so that the various guiding parameters used in PHD2 will make sense.

Guide Algorithm Parameters

In PHD2, the various guide algorithms can be applied to either the right ascension or declination axes. Most of these algorithms include
a minimum move parameter. This is used to avoid making guide corrections that are overly small, are unlikely to have any effect on star shape,
and are mostly due to transient seeing effects. These values are entered in units of pixels, so you need to think about them in the context of your
image scale and the typical size of your guide stars. If you have used the new-profile-wizard to configure your system, the min-move parameters
will be set to values that are likely to work well for the image scale you're using. The Guiding Assistant can also adjust these values based on its
measurement of high-frequency seeing disturbances. If you are seeing a high rate of declination guider corrections and lots of direction reversals,
you may be "chasing the seeing" and adjusting the min-move values upward can be a simple way to reduce that. Of all the detailed guiding
parameters discussed here, the two min-move values are the most likely to warrant adjustment on a nightly basis depending on
seeing conditions.

The hysteresis algorithms keep a history of the guiding corrections that have been made in the recent past, and these are used to help compute
the next guide correction. The hysteresis parameter, expressed as a percentage, specifies the "weight" that should be given to this history as
opposed to looking only at the star deflection in the current guide frame. Consider an example where the hysteresis parameter is 10%. In that
case, the next guiding correction will be 90% influenced by the star movement seen in the current guide frame and 10% by the corrections that
have been made in the recent past. Increasing the hysteresis value will smooth out the corrections at the risk of being too slow to react to a
legitimate change in direction. The hysteresis algorithms also include an aggressiveness parameter, again expressed as a percentage, that is used
to reduce over-correcting. On each frame, PHD2 computes how far it thinks the mount should move and in what direction(s) it should move. The
aggressiveness parameter scales this. For example, take a case where the star deflection has been evaluated and a corrective move of 0.5 pixels is
33
warranted. If the aggressiveness is set to 100%, a guider command will be issued to move the mount the full 0.5 pixels. But if the aggressiveness
is set to 60%, the mount will be asked to move only 60% of that amount, or 0.3 pixels. If you've done a reasonable job of setting Min-Move
values, there is generally no need to modify these parameters., and any modifications you attempt should be based on a careful analysis of your
guiding history using the PHD2 LogViewer tool.

The ResistSwitch algorithm behaves much as its name implies. Like the hysteresis algorithms, it also maintains a history of past guide corrections,
and any change of direction must be "compelling" in order to issue a reversing guide command. This is appropriate for declination guiding, where
reversals in direction are both suspect and likely to trigger backlash in the gears. For that reason, ResistSwitch is the default algorithm for
declination but not for right ascension, where valid direction reversals are expected. Starting with Release 2.4.1, two additional parameters are
available for fine-tuning the ResistSwitch algorithm. The first is "aggression", a percentage amount that controls how much of the computed guide
correction will be issued. Reducing this parameter can help to avoid over-shooting with mounts that have little or no backlash. The second
parameter is a checkbox labeled "Fast switch for large deflections." If this is checked, PHD2 will react immediately to a large change of direction
rather than waiting for three consecutive deflections in the new direction, which is the normal behavior. This can help to more quickly recover from
large excursions in Dec, perhaps caused by wind, cable snags, or other mechanical shifts The definition of a "large deflection" is 3x the minimum-
move value. So if PHD2 is over-reacting to direction changes, you can tune the behavior with the min-move parameter or disable the "fast switch"
option altogether. It is worth remembering that "less is usually better" when it comes to Dec guiding, so don't try to over-tune these parameters.

The LowPass algorithms also employ a history of recent guiding corrections in order to compute the next correction. The starting point for the
computed move is the median value of the guide star deflections that have occurred in recent history. This means that the star deflection seen in the
current guide frame has relatively little impact on calculating the next move and the algorithm is very resistant to quick changes. But the history
accumulation also includes a calculation to determine if deflections are trending in a consistent direction. The slope weight parameter, expressed
as a percentage, determines how much influence this should have in calculating the actual guider movement - it is there to keep the algorithm from
being overly sluggish. If you set a slope weight of zero, the guide pulse will always be just the median value of the recent history. If you set a non-
zero slope weight, that median value will be adjusted either upward or downward based on the recent trend of guide star movements. Because the
low-pass algorithm is so resistant to quick changes, it is probably most applicable to declination guiding or to mounts with absolute encoders. Use
of this algorithm has been deprecated in favor of the LowPass2 algorithm.

The LowPass2 algorithm is a variation of the original LowPass algorithm with somewhat different behavior. It also maintains a history of guiding
corrections, but the next correction is simply a linear extension of the commands that have come before it (i.e. a slope calculation). This continues
until a significant change in direction is seen, at which point the history is cleared. The algorithm has two adjustable properties: minimum-move and
aggressiveness. Minimum-move has the same effect as it does in the other guide algorithms, and aggressiveness (percentage) is a way of further
dampening the size of the guide corrections. LowPass2 is a very conservative, high-impedance algorithm that may be a good choice for users with
good seeing conditions and well-behaved mounts with little or no declination backlash. It is the recommended algorithm for mounts that have high-
precision encoders on the two axes.

The Z-filter algorithm is a variation on the LowPass algorithms but operates in the discrete frequency or "Z" domain. In terms of guiding it applies
full correction to the low frequency components caused by mount periodic error. Higher frequencies are corrected with aggression progressively
reducing down to zero.
The Z-filter algorithm allows you to use shorter guide camera exposure times (e.g. 1s or 0.5s) without chasing the high frequency seeing. The
advantages of shorter guide exposure time are reduced lag time for applying corrections and smaller corrections.
The Z-filter algorithm offers just two adjustments: Exposure Factor (XFac) and Minimum Movement (MinMo). The virtual guide exposure time is
given by the actual exposure time multiplied by the Exposure Factor. A given virtual exposure time will perform similarly to an unfiltered algorithm
using the same actual guide exposure time. For example, an exposure time of 1s with Exposure Factor of 4 gives a virtual exposure time of 4s (4 x
1s) and performs similarly to Hysteresis with Agression 100% and Hysteresis 0.0 using an exposure time of 4s. An exposure time of 2s with an
Exposure Factor of 2 also has a virtual exxpsoure time of 4s (2 x 2s) and thus performs much the same. The main difference is that the shorter
actual exposures allow the corrections to be applied sooner and more frequently so they are smaller.
This feature lets you adjust the guide exposure time to optimise the guide star SNR and guide latency. You can then adjust the Exposure factor to
get the desired guiding response. A virtual exposure time of 2s to 4s per the usual recommendation is a good starting point for the RA axis. On the
Dec axis, longer virtual exposures can be used and can help minimise reversals that can result in backlash.
Note that when using short exposures the movement from seeing will be more visible on the guiding graph. This does not mean the guiding is
worse. Other algorithms rely on guide exposure time to filter out the movement from seeing. The Z-filter Exposure Factor performs the same
function.
The Z-filter also has a MinMo setting. The value should be chosen to match the ability of the mount to accurately make small corrections. With
other algorithms MinMo is sometimes recommended to provide some filtering e.g. to prevent reversals of the Dec axis. With the Z-filter the
recommended approach is to increase the Exposure factor.

PHD2 Predictive PEC Guide Algorithm (PPEC)

Overview
34
 The PPEC algorithm is different from the others in PHD2 because of its modeling and predictive capabilities. The algorithm analyzes the tracking
performance of the mount in real-time and once that analysis is complete, it will compute guiding corrections even before a repetitive error is
actually seen. Issuing proactive guiding corrections reduces the time delay inherent in traditional guiding and can significantly improve
performance. With the other algorithms, which are completely reactive, guide corrections are issued only after the error has been seen on the
camera sensor.
Once guiding has begun, the algorithm analyzes the performance of the mount and looks for tracking errors that are repetitive and thus,
predictable. The algorithm employs a sophisticated Gaussian process model developed by a research team at the Max Planck Institute in
Germany. The mathematical details can be found in a paper referenced here:
http://ieeexplore.ieee.org/document/7105398/?reload=true
The PPEC algorithm will normally be used for RA, where residual periodic error and other gear-related errors often reduce tracking accuracy.
The algorithm uses separate time-scales for characterizing the behavior of the system:
Short-term: for high-frequency errors such as those caused by gear roughness or seeing
Medium-term: for residual periodic errors, typically occurring at intervals less than or equal to the worm period
Longer-term: for steady drift and for lower frequency (longer time interval) harmonics that can be caused by the interaction of multiple gears
in the drive train
The short-term behavior is used to identify the unpredictable noise in the system, which is essentially filtered out in order to identify components
that are predictable. For most mounts, the medium-term component is likely to be the most important. If you’re following best practices, you will
have programmed periodic error correction in your mount (assuming that feature is available to you). Doing this reduces the amount of work that
needs to be done by PHD2, and the PEC correction in the mount is normally saved permanently. This approach is preferable to having to
measure and infer the periodic error behavior every time you set up your equipment. That said, PEC in the mount is never perfect, and you will
often see residual repetitive errors even when PEC is active. These often arise when the tracking errors occur with a frequency that is not a
harmonic (integer fraction) of the mount’s worm period – most PEC implementations can’t deal with those. You can also get residual periodic
errors if they are dependent on the mechanical loading of the mount or if the mount’s behavior has changed since the PEC was programmed. The
PPEC algorithm can be quite effective at identifying and reducing these errors because it doesn’t depend on the worm period and is always doing a
fresh analysis of the mount’s current behavior.
The PPEC algorithm will also detect and proactively correct for drift errors. Although drift is typically handled well by any of the guide algorithms,
the corrections will always lag the error by some amount. For some use cases – perhaps spectroscopy, photometry or comet-tracking – this might
be a problem, in which case PPEC may deliver better results.
Since PPEC employs a learning process, it will usually take about 2 worm periods to model the mount and become fully effective. During this
training period, the algorithm will behave more like the ‘hysteresis’ algorithm, so you won’t normally see a performance penalty while the internal
model is being built. Instead, you’re likely to see a steady improvement in tracking as the model is refined and the algorithm shifts seamlessly from
hysteresis to predictive-mode. This improvement can usually be seen even before the medium-term mount behavior is fully modeled.
Since the PPEC model is implicitly tied to the state of the gear train, it must be re-learned if the mount is slewed by a substantial distance. For the
same reason, it can’t be retained across different guiding sessions, which is why conventional PEC is important. However, the PPEC model will
remain intact during dither operations and while guiding is paused (via automation) for activities like focusing. For the most common use-case,
namely imaging the same target for multiple hours with periodic dithering, the PPEC model will remain valid. In any case, the learning process and
transition from one mode to the other is handled automatically, so you won’t need to pay it any attention.
Algorithm Details
Once the training period is completed, the PPEC algorithm computes the guide correction using two factors. One is reactive, based on the
displacement of the guide star in the most recent exposure. The second is predictive, based on the output from the Gaussian process model
constructed during the training period. Each of these terms includes a separate gain or aggressiveness factor, so the final guide pulse amount is a
sum:
Guide-correction = (predicted amount * predictive gain) + (recent displacement * reactive gain)
The ‘predictive gain’ and ‘reactive gain’ parameters are exposed in the Advanced Settings dialog, and their default values for these parameters
should work well for most mounts. You should be conservative about changing them because bad choices for these parameters can definitely
make your guiding worse.
During the training period, the algorithm needs to identify periodic errors in the observed guide star movement. For initial trials, you can use the
worm period of your mount as the starting point for the ‘period length’. This gives the algorithm a good starting point, but you should also leave
the ‘auto-adjust period’ option checked. This tells the algorithm to adjust the period as needed to better control whatever periodic errors it finds.
Once you have run the algorithm multiple times and are happy with the results, you can leave this field set to whatever value was computed in the
previous sessions. If you have a mount with a recurring tracking error that occurs on a non-harmonic frequency, you may want to disable "auto-
adjust period' and "lock" the PPEC algorithm on the particular frequency you are trying to control. Obviously, knowing this requires an FFT
analysis of your native tracking performance, a capability that's part of the PHD LogViewer tool.
The 'Retain model (% period)' parameter specifies how long the mount can track unguided before the PPEC algorithm will be reset. This is
35
computed as a percentage of the current period length. This is useful in situations such as auto-focusing where the mount is continuing to track at
the sidereal rate but guiding isn't being done. It also applies to westward changes in the RA pointing position from slewing. Care must be taken if
the default setting of 40% is adjusted upward. Running for extended periods of time unguided causes the PPEC model to lose accuracy, in which
case a reset would be the best course of action. The point where that occurs is specific to the mount and the current seeing conditions, so you may
need to experiment if you want to adjust this parameter.
The ‘min-move’ parameter affects only the reactive component of the algorithm. If the measured star displacement is less than this amount, the
reactive component will be set to zero. However, the predictive component of the algorithm will still be computed and applied.

36
Tools and Utilities
Manual Guide
Auto-Select Star
Calibration Details
PHD2 Server
Dithering Operations
Logging and Debug Output
Polar Alignment Tools
Lock Positions
Comet Tracking
Guiding Assistant
Equipment Profiles
Ask for Coordinates Aux Mount
Simulator Parameters
Multiple Program Instances
Keyboard Shortcuts
Software Update

Manual Guide

If you are encountering calibration problems, you will probably want to be sure that PHD2's commands are actually getting to the mount. Or you
may want to nudge the mount or experiment with manual dithering. In the 'Tools' menu, click on 'Manual Guide' and a dialog will appear to let you
move the mount at guide speed in any direction. If you have an adaptive optics device attached, you'll see separate move buttons for both the AO
and the secondary mount. Each time you press the button, a pulse of the duration specified in the 'Guide Pulse Duration' field will be sent. The
default value is the 'calibration step-size' set in the Advanced Settings dialog. If you are debugging mount/calibration problems in the daytime, listen
to (rather than watch) your mount to determine if it is getting the commands from PHD2. The idea here is just to figure out if the mount is
responding to PHD2's signals. You won't be able to see the mount move (it's moving at guide speed) but you may be able to hear the motors.
Other options include watching the motors and gears or attaching a laser pointer to your scope and aiming it at something fairly far away (to
amplify your motions). A better approach for nighttime testing is to run the "star-cross" test described here.

Dithering is used primarily with image capture or automation applications using the PHD2 server interface. However, you can do manual dithering
or experiment with dither settings using the controls at the bottom of the dialog. The 'dither' amount field at the left controls the amount the mount
will be moved , in units of pixels. You can scale this amount - i.e. multiply it by a constant - by using the 'scale' spin control to the right. These two
controls establish a maximum amount of movement that will be used for dithering - the product of 'scale' X 'dither'. When you click on the 'Dither'
button, PHD2 will move the mount by a random amount that is less than or equal to the limit you have set, in one of the north/south/east/west
directions. The 'RA Only' checkbox will constrain the dither adjustments to only east or west. Obviously, if you are doing a manual dither in this
way, you'll want to be sure your imaging camera is not in the middle of an exposure.

Auto-Select Star
Automatic guide star selection can be accomplished in several ways. The simplest is to click on the 'Auto-Select Star' icon in the main window,
next to the 'Guide' icon. But it can also be triggered by using the keyboard shortcut of <Alt>S or by clicking on the ' Auto-select star' item under
the 'Tools' menu. Taking any of these actions tells PHD2 to scan the current guide image and identify a star most suitable for guiding. PHD2 will
try to select a star of sufficient brightness that is not saturated, has sufficient size, and is not too near another star nor too close to the edge of the
frame. The selected star may appear fairly dim on the screen, but that's usually not important - just adjust the gamma slider on the main window.
The auto-select function will almost always do a better job than you can just looking at the display. In many cases, a star you choose interactively
is at or near saturation and will produce sub-par results. You can use the Star Profile tool to examine the properties of the selected star, however
it was chosen. To get the best results from Auto-Select, you should definitely use either a bad-pixel map or dark library and specify a Min-HFD
value (Advanced Settings/Guiding tab) to reduce the likelihood of PHD2 mistakenly choosing a hot pixel. It also works better if you set the option
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to measure saturation by Max-ADU value (Advanced Settings/Camera tab), assuming you know or can determine the maximum ADU value of
your camera. For example, a 16-bit guide camera will have maximum ADU values approaching 65000.

To de-select the star and continue looping exposures, just shift-click on the 'Auto-Select Star' icon or shift-click anywhere in the image display
window. This can be useful if you're using sub-frames and want to return to a full-frame view of the guider images.

Calibration Details
Most of the calibration-related windows, including calibration sanity-checks, will open a window that looks something like this:

The first thing to look at is the graph to the left, which shows what star movements resulted from the guide pulses that PHD2 sent during
calibration. The lines represent the RA and Dec guide rates that were computed as a result of the calibration, and these lines should be roughly
perpendicular. The data points will never be perfectly aligned, but they should not have major curves, sharp inflections, or reversals in direction.
Particularly with longer focal length scopes, the points will often show considerable scatter around the lines, but this is normal. The solid points
(west and north pulses) are used to compute the RA and declination rates, while the hollow points show the "return" paths of the east and south
moves. These can help you see how much fluctuation occurred due to seeing and also whether there is a significant amount of backlash. If you are
using the "fast-recenter" option in the Advanced Settings, there may be many fewer points shown in the east and north paths. The tabular
information to the right shows what was known about the pointing position of the scope and the various ASCOM settings that relate to guiding. If
you are not using an ASCOM mount and don't have an "Aux mount" specified, some of this information will be missing. The table will also show
the expected guiding rates for a "perfect" calibration using the same sky position and guide speed settings you used. You will almost never achieve
these ideal values, and you shouldn't worry about them unless your values are very different. If you didn't see an alert message when the
calibration completed, your results are probably good enough. If you want to re-use a calibration for an extended time, it is probably worth a
few extra minutes to check this information and confirm that the calibration went reasonably well and produced sensible results. Bad calibrations
can occur even for very experienced imagers using high-end mounts, so it is good to check.

If you are having consistent problems getting alert-free calibrations, you should review the material in the trouble-shooting section .

Other Calibration-Related Menu Options

Calibration data are saved automatically each time a calibration sequence completes successfully. The use of the calibration data has been
described elsewhere (Using PHD Guiding), including options for restoring calibration data from an earlier time or "flipping" it after a meridian flip.
You access these functions using the 'Modify Calibration' sub-menu under the 'Tools' menu. Two other calibration-related items are shown there,
namely the options to clear the current data or to enter calibration data manually. The "clear" option accomplishes the same thing as the 'Clear
calibration' checkbox in the Advanced Settings dialog - it will force a recalibration whenever guiding is resumed. The 'Enter calibration data'
option should be used only under very unusual circumstances and only if you're sure you know what you're doing; but it is available as a matter of
completeness. If you click on the 'Enter calibration data' item, you'll see a dialog box that allows input of relatively low-level calibration data. This
data might come from a much earlier session, perhaps extracted from the PHD2 guiding log file. Keep in mind, if you are using an ASCOM driver
for either the 'mount' or 'aux mount' connections, you should have little need for these calibration data controls.

PHD2 Server
PHD2 supports third-party imaging and automation applications that need to control the guiding process. Sequence Generator Pro is probably the
most popular of these but there are numerous others. By using the PHD2 server process, image capture programs can control dithering between
exposures or suspend guide exposures while the primary imaging camera is downloading data. To use these capabilities with a compatible
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application, you should click on the 'Enable Server' option under the 'Tools' menu. The PHD2 server interface is quite extensive, and it's possible
for an application to control most aspects of PHD2's guiding operations. Documentation for the server API is available on the PHD2 Wiki.

Dithering
The primary purpose of dithering is to make post-processing easier by removing some kinds of fixed-pattern noise in the images, especially hot
pixels. This is primarily a function of the camera you're using and to a lesser extent, the sophistication of the post-processing software. For
imagers with temperature-regulated, low-noise cameras, dithering is mostly a convenient way to eliminate hot pixels that aren't getting removed by
the dark frames. Hot pixel positions change as sensors age, so dark libraries don't usually correct for all of them. Those hot pixels can also
be removed in post-processing, but that becomes tedious if there are lots of them. Dithering can help with some other kinds of sensor behavior
such as column defects, and it's particularly helpful if there is no temperature regulation on the sensor and therefore no good way to use a dark
library. DSLR imagers often use aggressive dithering to handle the substantial fixed-pattern noise usually present in those sensors. In the PHD2
implementation, automated dithering is accomplished through the server interface, so make sure you have 'Enable Server' checked under the
'Tools' menu. You first specify a maximum dither size you want to use during the guiding session - this will be set in your imaging application..
When that application issues a dither command, PHD2 uses a random number generator to decide how large the dither will actually be for that
command. The actual dither mount will be > 0 and <= the maximum amount allowed. Pseudo-random dither amounts like this are used to insure
that dithering doesn't follow a simplistic back-and-forth pattern or shift the frame back to a location where it has previously been. But for some of
the applications that do PHD2 dithering, you can't specify the maximum amount directly - you are perhaps limited to choices like
small/medium/large and the max dither amounts will have preset values. For that reason, PHD2 has a dither scaling parameter in the 'Global' tab of
the Advanced Settings dialog. It is basically a multiplier term that lets you adjust the range of dither amounts that are possible. So a scale factor of
1 doesn't change the preset value at all, a value of 10 multiplies it by 10X, etc. If you're using an app that lets you specify the maximum amount
directly (e.g. PHD_Dither), you should leave the dither scale set to 1.0. Otherwise, you can adjust the scale factor if you aren't happy with the
overall range of dithering you're getting with one of the small/medium/large type imaging apps.
There are typically two costs associated with dithering: 1) the extra time and uncertainty required for "settling" and 2) the need to crop the final
stacked frame in order to remove the low-signal margins. Settling is the term used for a period of stabilization after the mount has been moved by
a dither command. The imaging app that starts the dither will also decide when the guiding has stabilized enough to continue imaging. The app
can let PHD2 determine this by specifying the settling parameters or the app can do the calculations itself. You'll need to look at your
imaging/dithering app to see what control you have over this process. If the app uses the latest PHD2 server interfaces, it can specify a settling
requirement that might look like "guiding errors must be less than 1.5 pixels for a period of at least 10 seconds." This is a process that can
consume some time, depending on how tight the requirements are for settling. It is likely to take more time if you are dithering in declination and
the dither forces a change in direction. Most mounts have some declination backlash, so it can take a number of guide commands to get the mount
moving in the right direction, and then more time for the process to converge on the new target location for the guide star. That's why PHD2 also
offers the option to dither only in right ascension. Again, this is an option on the 'Global' tab, right next to the dither scaling parameter. Mounts
with substantial Dec backlash or setups that need a large amount of dithering can benefit from using the "spiral mode" (. With this approach,
neither the dither size nor the direction is randomized. Instead, PHD2 issues a fixed-size dither while forcing the direction to trace out an
expanding spiral around the original lock-point.
If your mount has a substantial amount of declination backlash in the mount, you may be guiding in only the north or south Dec direction. If PHD2
receives a command to dither in declination while you're operating in this mode, it will temporarily allow guiding in both Dec directions until the
dither and settling are completed. It will then revert to the original north/south-only guiding mode. If you don't want this behavior, you should
restrict dithering to 'RA-only'. All of the PHD2 dither controls are contained on the 'Global' tab of the Advanced Settings dialog.

Logging and Debug Output

PHD2 automatically creates two types of log files: a debug log and a guiding log. Both are very useful for different reasons. The guide log is
intentionally formatted to allow easy interpretation by either a human reader or an external application. For example, the PHDLogView application
(not part of the PHD2 release) can produce a variety of graphs and summary statistics based on data in the PHD2 guide log. But the log can also
be easily imported into Excel or other applications for analysis and graphing. When importing into Excel, just specify a comma as a column
separator. The debug log has a complete record of everything that was done in the PHD2 session, so it is very helpful in isolating any problems
you have. It also employs a human-friendly (albeit verbose) text format, so it's not difficult to examine the debug log to see what happened. If
you need to report a problem with the software, you will almost certainly be asked to provide the debug log file. If you have neither log file
available, you are unlikely to get any help.

The location for the files is controlled by the 'Log File Location' field in the 'Global' tab of the 'Advanced Settings' dialog. By default, log files are
stored in the OS-specific default directory for user documents. In Windows, for example, the files will be stored in a 'PHD2' sub-folder in the
"Documents" directory. This may not be a convenient location, so you can specify a different folder using this edit field. In order to prevent
excessive accumulation of log files, PHD2 automatically removes debug logs that are more than 30 days old and guide logs that are more than 60
days old. If you want to retain the files for longer periods, you should move or copy them to a different folder location, one not used by PHD2.

To simplify the automatic log upload process (see below), log data is grouped by "imaging day", defined to be a 24-hour period beginning at 09:00
am local time. This means that all the PHD2 executions on the same imaging day will write guiding and debug log data into the two log files for that
imaging day. Logging is always active regardless of what was done (or not done) during the time that PHD2 was running.

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In some unusual cases, you may need to capture guide camera images, usually to support debugging and problem resolution. This can be done by
clicking the 'Enable Star Imaging Logging' menu item under the 'Tools' menu. The resultant image files will be stored in the same location as the
other log files. The format of these image files is controlled from the 'Global' tab of the 'Advanced Settings' dialog. If you are trying to document a
problem you're having, you should choose the 'Raw Fits' format for maximum flexibility.

Automatic Log File Upload

If you need help using PHD2 or improving your guiding results, you'll want to post a request on the Open-PHD-Guiding forum
(https://groups.google.com/forum/#!forum/open-phd-guiding). Your question should be accompanied by the PHD log files associated with the
guiding session you're talking about. Please do not edit, trim, or rename the log files. To make uploading easier, PHD2 has a built-in function to
select, compress, and automatically upload the relevant log files. That function is located on the 'Help' menu. You'll see a dialog box that shows all
the available log files, including their timestamps and duration:

Just select the files you want and start the upload process by clicking on 'Next'. Please be careful to look at the 'Session Start' and 'Duration'
columns to be sure the log covers the time period you're interested in. PHD2 creates guide and debug log files every time it's run, so some of the
log files will be nearly empty - don't upload those. If PHD2 is generally working for you but you can't interpret the guiding performance or you
want to improve it, you can start by just uploading the guide logs. But if you're having trouble with camera or mount connections or otherwise can't
get PHD2 running, you should also include the matching debug log file. Be selective about the files you choose - just the files for the session you
were having trouble with. When the upload process is complete, you'll see another window that gives you a link to the files:

You need to capture or record that link so it can be included with the question you'll post on the forum. Log files will be automatically removed
on the server after a reasonable amount of time has elapsed, so you won't need to worry about that. When you post your request for support,
please include a full description of what you were doing, whatever problem you saw, and roughly what time period you want us to focus on.

Polar Alignment Tools

PHD2 offers three different polar alignment tools. The three approaches share the same basic objective: to help you physically align the RA axis of
your mount to the celestial pole. These polar alignment tools are different from the “two-star” or “three-star” alignment procedures that are part of
many popular go-to mounts. The mount software routines are generally focused on optimizing go-to operations, correcting the slewing/pointing
operations for a variety of errors in the mount, including polar alignment error. They generally don’t involve physical adjustment of the mount’s
azimuth and altitude controls, which is what is necessary for successful imaging and guiding.

The three polar alignment tools have different requirements and behaviors, as summarized in the table below. The accuracy and speed columns
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show values in the range of 1-3, where 1 is lowest and 3 is highest.

Method Accuracy Speed Sky View Other

Requires identification of polar region stars
Static polar alignment 1 3 Polar region
Minimal slewing
Polar drift alignment 2 2 Polar region Minimal slewing
East or west horizon Most slewing
Traditional drift alignment 3 1
Meridian/celestial equator Axes measured/adjusted separately

The original polar alignment routine, drift alignment, is still considered by most to be the “gold standard” for accuracy. Partly, this is because it
directly measures the thing you’re interested in: the amount of drift that will be caused by mis-alignment of the RA axis on the celestial pole. The
drift alignment tool requires use of only one visible star at a time, and identification of the star is unnecessary. But the procedure can be time-
consuming, especially for beginners, because each mount axis must be adjusted separately and the telescope will need to slew over a fairly wide
area. Also, it works best if you have clear views of the celestial equator/meridian intersection and an area around 30 degrees above either the
eastern or western horizon (azimuth 90 or 270 degrees). For imagers who are rushing to set up each night or have a limited view of the sky, these
requirements may be unattractive.
The second alignment option, static polar alignment, addresses these concerns by taking a different approach. It specifically trades off
some accuracy to optimize the speed of the process. It requires only a clear view of the northern or southern polar region, and it facilitates
adjustment of both mount axes at the same time. It is therefore a bit more intuitive and quite likely to be quicker to complete. It does require
visibility and identification of several stars near the pole, but the tool makes that reasonably easy assuming your sky conditions are good enough to
see the stars.
The third alignment option, polar drift alignment, is probably the simplest one to perform at the expense of a bit of accuracy and speed. It requires
a clear view of the northern or southern polar region, and it facilitates adjustment of both mount axes at the same time. Minimal user input is needed
so it is very simple to use.
The three techniques are described in detail in the following sections. Imagers should probably experiment with them and choose the one that best
suits their needs. The importance of alignment accuracy is often over-emphasized, so users need to keep things in perspective. Most declination
drift can be well-managed by PHD2 guiding assuming the mount behaves well and doesn’t have a lot of declination backlash. However, at some
point, the amount of polar alignment error can create field rotation in the images, something that can’t be corrected. The larger the imaging sensor
and the closer to the pole the target is, the more field rotation can be an issue. You can compute the expected field rotation using an online
calculator such as this one:
http://celestialwonders.com/tools/rotationMaxErrorCalc.html
The calculator can help you decide how much accuracy is “good enough” for your situation. It’s also important to remember that any of the
procedures can be limited by the precision of the adjustment mechanisms on the mount.

Drift Alignment Tool

Static Polar Alignment Tool
Polar Drift Alignment Tool
Lock Positions
PHD2 normally sets a 'lock position' where the guide star is located at the end of a calibration. Depending on the details of the calibration
sequence, this may not be exactly where the star was located at the start of calibration - it could be off by a few pixels. If you are trying to
precisely center your target, you may want to use a 'sticky lock position.' You do this by clicking on your guide star before calibration, then
setting the 'Sticky Lock Position' under the 'Tools' menu. After calibration is complete, PHD2 will continue to move the mount until the star is
located at the sticky lock position. So you may see an additional delay after the calibration while PHD2 repositions the scope at guide speed. The
sticky lock position will continue to be used even as guiding is stopped and subsequently resumed. Again, this insures a rigorous positioning of the
guide star (and presumably your image target) at the expense of delays needed for PHD2 to reposition the mount.

If you need to fine-tune the position of the guide star on the camera sensor after guiding has begun, you can use the 'Adjust Lock Position' function
under the Tools menu:

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You can nudge the guide star in small increments (at guide speed) or you can move it by a larger amount by typing in a new lock position and
clicking 'Set'. Clicking on the up/down/left/right buttons will cause the lock position to be shifted in the corresponding direction by the amount
shown in 'Step', and the revised lock position will be displayed If you type in a new lock position, you run the risk of losing the guide star if the
new position falls outside the current search region. This tool is useful if you need to achieve precise positioning of either the guide star or the
imaging target, for example with spectroscopy..

Comet Tracking
One way to image a comet is to have PHD2 use the comet as the guide "star", but this approach may not always work. For example, the head of
the comet may not present a star-like center suitable for guiding. Or, when using an off-axis guider, the comet may not even be visible in the guide
camera.

PHD2 provides a Comet Tracking tool for use when guiding on the comet itself is not feasible. The idea is to guide on an ordinary star, but to
gradually shift the lock position to match the comet's motion, or tracking rate.

There are a three different ways to provide the comet tracking rate to PHD2.

Some planetarium applications, like Cartes du Ciel, can send the rate directly to PHD2;
You can enter the tracking rate manually, or,
You can train the rate in PHD2 by following the comet for a period of time in the imaging camera.

To enter the rates manually, you would select "Arcsec/hr" for units and "RA/Dec" for axes, then enter the rates from the comet's ephemeris. If you
are getting the rates from the MinorPlanetCenter web site, you should choose the option for 'Separate RA and Declination coordinate motions'.
PHD2 will automatically adjust the rates to compute the apparent motions in the sky.

Comet rate training works like this:

First, center the comet in your imaging camera. If your imaging application has some kind of reticle display, you should use that to note the precise
position of the comet on the imaging sensor. Once this is ready, select a guide star in PHD2 and start guiding. Next click "Start" in the Comet
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Tracking tool to begin training.

Take a continuous series of short exposures in your imaging camera using your imaging application's Frame and Focus feature. Over time, the
comet will drift away from the starting location. Use PHD2's "Adjust Lock Position" controls to move the comet back to the starting location. You
may have to experiment a bit to determine which way the comet moves on the imaging camera sensor in response to the Up/Down/Left/Right
controls in PHD2. You may find it useful to enable the "Always on top" button in the Adjust Lock Position window so the controls stay visible on
top of your imaging application.

PHD2 will quickly learn the comet tracking rate as you re-center the comet. Once you are satisfied that PHD2 is tracking the comet, you can click
Stop to end the training. PHD2 will continue shifting the lock position to track the comet until you disable comet tracking by toggling the
Enable/Disable button.

You can practice the comet training technique using the built-in camera simulator. Check the "Comet" option in the Camera Settings dialog, and the
simulator will display a comet. Use a bookmark to mark the comet's starting location, and use the Adjust Lock Position controls to move the
comet back to the bookmark location.

Guiding Assistant
The Guiding Assistant is an instructional tool to help you measure current seeing conditions and the general behavior of your mount and guiding
subsystem. When it's run, it temporarily disables guiding output and measures the ensuing motion of the guide star. This can help you see the high-
frequency motions caused by seeing (atmospheric) conditions. These cannot be corrected by conventional guiding because they occur at a much
higher frequency than you can typically even measure. Trying to correct for them with conventional guiding is often called "chasing the seeing" and
usually leads to poor results. Avoiding it is best accomplished by setting a minimum-move level that will cause PHD2 to ignore most of this high-
frequency behavior. The Guiding Assistant can also show you other behavior of your system such as overall drift rates in right ascension and
declination as well as peak-to-peak and maximum-rate-of-change measurements in right ascension,. While these things can usually be "guided
out", measuring them can be helpful if you want to improve the underlying performance of the mount - for example, by improving your polar
alignment if the declination drift rate is high. The Guiding Assistant can also measure the declination backlash in your system if you select that
option in the user interface.

When you start the Guiding Assistant (GA), its behavior depends on whether you are already guiding. If guiding is active, the initial screen will
look like this (with different data values of course):

The topmost field in the form always shows what the GA is doing and what action you should take, so you should always look there first if you
don't know what's happening. In this case, the measurement process has been started automatically and you should simply let it run for at least
two minutes. The text field immediately above the buttons also summarizes what's happening. The three buttons are enabled or disabled based on
the operating state of the GA. In this case, 'Start' is disabled because the measurement is already underway.

If you launch the GA when guiding is inactive, the initial form will look different:
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In this case, you'll need to first start guiding in PHD2 - start looping, select a star, and guide. Once that's done, the 'Start' button in the GA will be
enabled and you can begin measurement.

When GA measurement is active, guiding commands will be disabled, so the star will appear to wander around on the display - this is entirely
normal. As guider images are acquired, statistics are computed and displayed in real-time in the user interface. After about two minutes of data
collection, the more volatile measurements like High-frequency Star Motion and Polar Alignemt Error will usually stabilize and you will probably
have reasonable overall measurements. If you want to get a more accurate measure of your polar alignment error and any uncorrected periodic
error in RA, you'll need to let the Guiding Assistant run for up to 10 minutes. Also, the computed polar alignment error is sensitive to the current
scope declination. To get the most accurate measurement, you should point the scope to within a few degrees of the celestial equator, the same
area you should use for calibration.. When you finally click the 'Stop' button, this phase of the measurement process will stop. If you've checked
the box to 'Measure Declination Backlash" that process will commence (see below). If not, guiding commands will be re-enabled and the data
collection process will end. Other computed results will be displayed in the lower area of the table showing overall drift rates and various other
measurements. All of these values are displayed in units of both arc-seconds and pixels. The dialog box will look something like this:

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The contents of the 'Recommendations' group on the right side of the window reflect the results of the statistical measurements. Assuming your
chosen guide algorithms support a minimum-move property, you have the option of automatically setting those parameters based on the results.
You can also decide to re-run the measurements or close the dialog box altogether if you want to proceed with normal guiding operations.

Measuring Declination Backlash

If you've checked the box to 'Measure Declination Backlash', that process will begin as soon as the high-frequency measurements are completed.
In other words, clicking once on the 'Stop' button halts the high-frequency measurements and begins the measurement of declination backlash.
However, if the initial sampling period was less than 2 minutes, a dialog box will appear and the backlash test will continue to sample until the 2-
minute period has expired. A new group of status messages will be shown immediately above the 'Start' and 'Stop' buttons so you can see what's
being done:

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To do backlash measurement, PHD2 will move the star by large amounts, first in the north direction, then back to the south. There is some risk
the star will be lost during this process or the star might already be too close to the north edge of the sensor. You should choose a guide star that
has plenty of room to move north to get the best accuracy. If the star is lost because it's been moved outside the search region, you can
temporarily increase the size of that region from the 'Guiding' tab of the Advanced Settings dialog. A search region size of 20 pixels should work
for most configurations - just be sure you don't have multiple stars inside the search region. The first phase of backlash measurement involves an
initial attempt to clear whatever backlash is present in the north direction. The Guiding Assistant (GA) will continue with these clearing commands
until it sees a significant and consistent movement of the guide star in one direction. Once this is done, the GA will issue another sequence of
commands to continue moving the star north by a large amount. This will take at least 16 seconds and may take longer depending on the
configuration - you can watch the status update to see what's being done. When the north steps are finished, the GA will issue an identical number
of steps in the south direction. If there's significant backlash in the mount, it may take a long time for the star to start moving south, but that will
usually be handled. Once the south steps are done, the GA will try to compute an accurate estimate of the backlash amount, corrected for
Declination drift. This won't be done if the mount never established a consistent rate of south movement that was at least 90% of the measured
rate moving north That situation usually indicates binding in the Dec axis or substantial imbalance, in which case a simple estimate of backlash will
be inaccurate and probably irrelevant. You can always use the 'Show graph' button to see what happened during the test even if no estimate is
produced. When the test is completed, the GA will try to move the star back close to its starting position and will re-enable guiding. Again, there
is some risk the star may be lost, but this won't affect the calculations - you can simply stop and resume guiding as you normally would. Unlike the
first process for measuring high-frequency star movement, you don't need to click on the 'Stop' button once backlash measurement has begun.
The measurement process will terminate when all the steps have been completed, and normal guiding will be resumed. However, you can click on
the 'Stop' button if something has gone wrong - such as a lost-star condition - and then restart when you're ready. When the backlash tests are
finished, you'll see the results displayed as before, with the addition of entries for the amount of declination backlash and the measurement
uncertainty (or a status line that says the test failed):

Depending on the amount of backlash, you may see a recommendation for setting a backlash compensation factor - 230 ms in the example shown
above. This type of backlash compensation is different from the feature offered in many mount controllers and is described here: PHD2 backlash
compensation If the measured amount is less than 100 ms, no recommendation will be made because such a small amount probably doesn't
warrant any compensation. If the backlash is very large, over 3 seconds, you'll see a different recommendation to use uni-directional guiding in
declination. That's because trying to compensate for such large values probably won't work very well, and the mount will probably not be able to
reverse directions quickly enough to support bi-directional guiding. Obviously, you can reach your own conclusions based on your experience with
how the mount behaves. Before doing these measurements, be sure to disable any backlash compensation that's previously been enabled in the
mount software. If this isn't done, the measurements and any subsequent attempts at compensation by PHD2 will be invalid. If you want to try
uni-directional guiding, you can find instructions here: Uni-directional guiding

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You can look at a graphical display of the backlash measurement results to get a better understanding of how the mount performed even if the test
failed. Just click on the 'Show Graph' button to see a graph that might look something like this:

The green points show the measured declination positions, shown left to right, beginning with the north moves and ending with the south (return)
moves. The white points show the south-return behavior for a perfect mount with zero backlash. In this example, there is only a small amount of
backlash as evidenced by the flattened top of the green points. However, the flattened top will be more pronounced when there is significantly
more declination backlash in the mount, as in the following example:

The 'Review Previous' button at the bottom of the window lets you review the previous three GA results. If you've run backlash tests at any time,
at least one of the three sessions will include a backlash measurement result. Clicking on the 'Review' button displays a list of timestamps when a
GA was run for the current profile, so you can just select the date/time you want. All the grid values and recommendations will be filled with the
results from the selected GA run, including active buttons for applying the recommendations.

Star-Cross Tool
The star-cross tool can help you test the mount's response to guide commands as described in this trouble-shooting section. Although the test is
easy to perform manually, you may prefer to use this tool. The star-cross tool will show the following dialog:

47
This test presumes you're using the main image camera to expose the image, so PHD2 doesn't know what image scale is being used for
that. You'll need to be sure the settings are large enough to show a distinct pattern on the main camera but not so large that the stars will move out
of the field of view. The default settings should work well for most set-ups but you can adjust them as needed. The important thing is to get a
clear record of the movement of the stars in the main camera image and to save that image in a raw, uncompressed format (eg. FITs or
uncompressed TIF). During this test, looping will be active but no guide star will be selected, and it doesn't matter if individual stars move out of
the guide camera frame. Looping is activated just so you get some quick visual feedback on whether the mount is moving.

Meridian flip calibration Tool

The meridian flip calibration tool (wizard) is used to automatically determine the correct value for the setting Reverse Dec output after meridian flip.
Running the tool involves two calibrations -- one with the telescope on the East side of the pier, and one on the West. You will be instructed to
slew (meridian flip) the telescope when needed. This only needs to be done once for each type of mount you use.

Managing Equipment Profiles

Equipment profiles were introduced in the section on Basic Use where they are used as part of the 'Connect Equipment' dialog. If you want to
manage multiple profiles, you will probably want to use the 'Manage Profiles' button in the 'Connect Equipment' dialog. Using the menu items
there, you can create a new profile or edit/rename/delete an existing one. Each profile holds all the settings that were active at the time the profile
was last used. If you create a new profile, you can import these settings from either the PHD2 generic defaults or from an existing profile. You
can also use the 'Wizard' option to have PHD2 establish settings that are specific to your equipment configuration. To edit the settings in an
existing profile, you first select it in the equipment profile drop-down list, then click on 'Settings' under the 'Manage Profiles' pull-down. This will
take you to the Advanced Settings dialog, where you can make whatever changes you want. Remember that profiles are automatically updated
anytime settings are changed during a PHD2 session. Finally, you can import and export profiles for purposes of debugging, backup, or exchange
between computers.

Aux-Mount Connection using "Ask for coordinates"

If you can't connect to your mount using either ASCOM or INDI drivers, you still have a better-than-nothing alternative by using the "Ask for
coordinates" aux-mount connection. With this option, you'll be asked to enter or confirm the scope position each time guiding is going to begin::

If you enter your scope's current declination and side-of-pier values, PHD2 will automatically adjust the calibration to match that pointing position.
You don't need to be precise, a Declination value that's within a few degrees will work. This means you won't need to recalibrate as you slew to
different targets so long as you update these values each time. For example, you can do a calibration near Declination=0 then enter new position
values when you've slewed to a high declination imaging target. This is likely to produce a better result than trying to calibrate at a near-pole
48
position. This dialog will not be displayed if the start of guiding is the result of a dither operation or a server command from an imaging application.
In order for the calibration adjustment to work correctly, your previous calibration must have been completed with correct positioning data
available.

If you're using this option with the Drift Alignment tool, the dialog will look a bit different:

If you enter the additional information for Right Ascension, latitude, and longitude, the Drift Alignment tool can more accurately adjust its magenta
target circle. Otherwise, the circle will show only an upper-bound estimate of the pointing error during the 'adjustment' phases.

You can connect or disconnect the "Ask for coordinates" aux-mount without affecting the camera or mount connections. So you might decide to
use the option for drift alignment or for an initial slew to your imaging target, then disconnect from it in order to avoid the repetitive dialog displays.
Regardless of how you choose to use it, you're responsible for having the correct values in place, and you should remember that significantly
wrong values can result in poor guiding results.

Advanced Settings for the Simulators

The device simulators were introduced in the Basic Use section as useful tools for experimenting with PHD2 and becoming familiar with its
features. Remember that you must choose 'Simulator' as the camera type and 'On-camera' as the mount type in order to get the benefits of
simulation. As you become more interested in the details of the simulation, you can use the 'Camera Settings' button on the main display to adjust
the simulation parameters:

You can adjust simulated mount behaviors for declination backlash, drift due to polar mis-alignment, and periodic error. You can also adjust the
49
'seeing' level, which will create fairly realistic guide star deflections that look like seeing effects. If you adjust these parameters one-by-one, you'll
see how they affect star deflections and how the different guide algorithms react to those movements. Of course, you're dealing with a "nearly
perfect" mount in these scenarios (except for backlash), so the simulation can't be entirely realistic.

Multiple Program Executions

In some situations, you may want to run multiple instances of PHD2 at the same time. To start the second instance of PHD2, you need to supply a
command-line parameter of -i 2; the third instance would be started with -i 3, etc. You can accomplish this in Windows by running PHD2 from a
command line using the Windows cmd.exe utility. Or you can create a Windows desktop shortcut by doing the following:

Right-click on your desktop

Select: New/Shortcut
Enter the following string to identify the location of the program: "C:\Program File (x86)\PHDBuiding2\PHD2.exe" -i2
Click Next
Enter a name for the shortcut, e.g. PHD2 #2
Click Finish

Note the quotes around the name in the 3rd line are required by Windows because there are blanks embedded in the directory name.

Keyboard Shortcuts
Keyboard shortcuts are available for many of the more commonly used tools and functions in PHD2. These are enumerated in the Keyboard
Shortcuts section.

Software Update
One of the most common responses to a request for support in the PHD2 Forum is: please upgrade to the latest version and see if the problem still
exists. If you are seeing an issue in an older version of PHD2 it is quite likely that you are not the first person to encounter it, and that it has already
been reported and fixed in a newer version of PHD2. For this reason, the developers of PHD2 feel that it is important to be running the most up-
to-date version of the program.
Upgrading a program that you rely on for unattended imaging in our limited available clear sky time can sometimes be perceived as a risky
proposition. The developers of PHD2 recognize this sentiment--we are imagers too! There is a necessary trade-off between maintaining a stable
software installation and staying current with the latest bug fixes and other improvements.
PHD2 achieves a balance between these two opposing needs by publishing two series of software releases. The development releases contain the
latest ongoing bug fixes and feature improvements and are tested by the developers--usually during actual imaging time--before being released.
Users who choose to run the development releases will get the latest bug fixes and newest features. Development releases have names like
"2.6.3dev6" indicating, for example, the 6th development release after the 2.6.3 major release.
Periodically, after a development release has received more test time, it will be published as a major release. For example, 2.6.3dev6 could be
published as major release 2.6.4.

Checking for updates

PHD2 has an option to automatically check for software updates. We recommend enabling this option to help keep your version of PHD2 up to
date. When the automatic check option is enabled, PHD2 will quietly check for updates in the background when PHD2 starts. If new updates are
available, PHD2 will give you the option to install the new version. Enabling the automatic check for updates will not interfere with the ordinary
operation of PHD2, including automated operation. It is also safe to leave the option enabled if you are imaging in the field without internet
connectivity. If PHD2 cannot check for updates, it will wait until the next time it is started before trying to check again.
Regardless of whether you allow PHD2 to automatically check for updates at startup, you can always manually check for updates by clicking
"Check for updates" from the Help menu.

50
Table of PHD2 keyboard shortcuts
Shortcut Function
F1 Help
Ctrl-C Open Connect equipment window
Shift-Ctrl-C Connect all equipment
Ctrl-L Loop
Alt-S Auto-select Star
Ctrl-G Guide
Ctrl-S Stop
Ctrl-D Dismiss alert
Alt-C Review calibration
Ctrl-O Clear calibration (force re-calibration)
Ctrl-A Open Advanced settings
B Toggle Bookmarks shown/hidden
Ctrl-B Delete all Bookmarks
Shift-B Bookmark lock position
Shift-Ctrl-M Enter Manual calibration

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Trouble-shooting and Analysis
Calibration and Mount Control Problems
If you are just starting to use PHD2 or are connecting to new equipment for the first time, you may have trouble getting calibration done. This
problem usually takes one of two forms, each requiring different responses:
1. The star moves during calibration but it moves "too far" or "too little." If you've used the new-profile wizard and have provided correct
values for focal length, camera pixel-size, and mount guide speed setting, the "step-size" used in calibration should already be correct. But if
you've configured your profile by hand or have changed guide speed settings in the mount, you may need to adjust the 'calibration step-size'
parameter in the 'Guiding' tab of Advanced Settings. The help content there describes how this parameter is used, and you should be able to
resolve the problem quickly. But if you've used the new profile wizard and are seeing problems with "too far" or "too little" guide star
movement, the problem probably lies elsewhere.
2. The star doesn't move enough during RA calibration, declination ('Dec') backlash clearing, or Dec calibration. These problems are
announced by alert messages at the top of the display window. With longer focal lengths, small movements may even be the result of
seeing deflections, and the mount isn't really moving at all. Dealing with this sort of problem is described next.
In nearly all cases, the "no movement" problem is caused by failures in the mount or in the cabling and connections. The best tool for trouble-
shooting this is the 'Manual Guide' option under the 'Tools' menu, as described in the Tools section of this help document. Simply use the
directional controls in the 'Manual Guide' window to send commands directly to the mount while watching a star in the image display window. Use
fairly large guide pulse amounts - at least several seconds - so you can clearly see if the mount is moving. Try to move the mount in all four
directions and verify the target star is moving by roughly equal amounts. If the mount does not respond, you know you have either hardware or
connectivity problems to resolve - nothing to do with PHD2. If you're using a Shoestring device to connect to the mount, watch its indicator lights
to see if the commands are reaching it. Similarly, your ST-4 compatible guide camera may have indicator lights to show when guide commands
are being received. If you're using an ASCOM connection to the mount, be sure the COM port assignments are correct. You can also use some
of the ASCOM-supplied tools like POTH to be sure the ASCOM driver is communicating correctly with the mount. It is best to use the latest
version of the ASCOM driver for your mount because older versions of these drivers might have bugs associated with pulse-guiding.

Calibration Sanity-Checks and Alerts

It is also possible that the calibration process will complete but PHD2 will post a calibration alert message saying that some of the results are
questionable. These message do not mean that the calibration failed or is unusable, but they are warning you that some of the results don't look
quite right. Such a "sanity check" dialog will show an explanation of the issue and some details of the calibration results:

There are currently 5 things checked by PHD2 as part of calibration::

Too few steps (shown above) - resolving this issue can be easy assuming the mount is actually working correctly. Just adjust the
calibration step-size downward until you get at least 8 steps in both the west and north calibrations. If you used the new profile wizard to
set up your configuration, a good starting value for calibration step-size will already be set. If you find that the number of steps in RA and
Declination is substantially different, you are probably seeing evidence of declination backlash unless you are using different guide speed
settings on the two axes.
Orthogonality error - the camera axes are normally computed independently even though they should be perpendicular. The angle
calculations do not require great precision, but if they are significantly non-orthogonal, you should repeat the calibration. If you see
repetitive alerts of this type and the axes are significantly non-orthogonal, you'll need to identify the problem and fix it. Common causes are
52
 bad polar alignment, large declination backlash, or large periodic error in RA. Any of these problems can cause the guide star to move
significantly on one axis while PHD2 is trying to measure its motion on the other axis. If you suspect these problems, go ahead and accept
the calibration, then run the Guiding Assistant to measure your polar alignment error, declination backlash, and RA tracking error. In other
cases, the mount may not be moving at all, and the measured displacements of the star are just caused by seeing effects. This sort of
problem should be obvious in the calibration graph at the left of the dialog. If the axis error is relatively small and you are convinced the
hardware is working properly, you can avoid further alerts of this type by setting the option to 'Assume Dec orthogonal to RA' in the
'Guiding' tab of the Advanced Settings dialog. But you should do this only if the error is fairly small - otherwise, you are simply ignoring a
serious problem.
Questionable RA and Dec rates - assuming the guide speeds reported by the mount are accurate, the measured guide rate for right
ascension should be related to the declination guide rate by approximately a factor of cosine (Declination). In other words, the apparent RA
rate gets smaller as you move the scope closer to the pole. PHD2 won't try to identify which rate is incorrect - it is simply alerting you that
something looks wrong with the rates. You can sanity check these rates yourself quite simply. If you are guiding at 1X sidereal rate, your
declination guide rate should be approximately 15 arc-sec/sec; with a guide rate of 0.5X sidereal, the declination rate would be 7.5 arc-
sec/sec, etc. A declination rate that is significantly smaller than the RA rate is often an indication of substantial declination
backlash. Using a calibration that triggered this alert can lead to over-shooting in Dec guiding because the actual guide rate is probably
larger than the measured one. To work around this problem, you should manually clear the Dec backlash before starting calibration. You
can do this in either of two ways: 1) make sure the mount's last slew direction was north or 2) use the hand controller to manually move the
mount north at guide speed for 10-20 seconds.
Inconsistent results - if the calibration results are significantly different from your last-used calibration, an alert message will be generated.
This may happen because you've made a change in your configuration. That doesn't imply a real problem, but you should probably
consider creating a separate profile for the new configuration. By doing so, PHD2 will remember settings for each of your profiles, letting
you switch between them easily. If you haven't made a configuration change, you will probably want to determine why the results are so
different.
Too little east or south movement - The calibration process only uses the west and north moves to compute the camera angle and rates
of movement. The east and south moves are done primarily to restore the guide star somewhere close to its starting position. If little or no
east or south movement is seen, you may see an alert message advising you of the situation. The calibration hasn't failed, but guiding is likely
to be impaired. The most common causes are a defective guide cable if using ST-4 guiding or very large Declination backlash if the alert is
related to south moves.
With any of these alerts, the relevant data field will be highlighted based on the type of message. You can choose to ignore the warning ('Accept
calibration'), re-run the calibration ('Discard calibration'), or restore your last good calibration ('Restore old calibration'). With the third option,
you can defer calibration until later and start guiding with your last good calibration data. If you see repeated alerts on the same topic and are
convinced there really isn't a problem, you can use the 'don't show' checkbox to block future alerts of that type. But you should be aware that the
sanity-checking used by PHD2 works well for a wide range of equipment, and most users don't see these calibration alerts at all.

Declination Backlash
By far the most common source of calibration problems is declination backlash, which is present to some degree in most geared mounts. With
many less-expensive mounts, however, the problem can be severe and can lead to poor calibration and guiding results. Consider the following
example of a calibration review dialog:

The first clue to the problem is found by comparing the number of steps required for calibration on the two axes - 10 for RA but 42 for Dec. This
shows the mount was not moving consistently in declination, probably because the backlash had not been cleared. This also explains the
"wandering" behavior of the declination points (light green) when the guide commands were reversed from north to south. Finally, the computed
declination rate is much smaller than the RA rate even though the guide speed settings on the two axes were identical. In fact, this would have
53
triggered a calibration alert dialog. There are actually two problems to be addressed here. First, the calibration result is poor and should be
repeated in order to get a more accurate measure of the declination guide rate. Second, the mount is likely to behave badly during direction
reversals in declination even if the dec guide rate is correct. The calibration can be improved by first manually moving the mount north at guide
speed for 10-20 seconds until consistent star movement is seen in the main window. You can do this with the 'Manual Guide' tool or by using the
hand-controller on your mount. Once this is done, most of the declination backlash in your mount should have been overcome. You can then
repeat the calibration procedure and probably get a declination guiding rate that is more reasonable. The underlying backlash problem generally
requires some mechanical adjustment to the mount. If the mount isn't using a guide speed close to 1x sidereal, you can probably get an immediate
improvement by increasing the mount guide speed. You can also try using a PHD2 backlash compensation setting, but this is not likely to work
well if the backlash is large - more than 3 seconds, for example. If you can't correct the backlash or reduce it to manageable levels, you should
consider choosing uni-directional guiding for declination. To do this, you determine which way the mount drifts due to polar alignment error and tell
PHD2 to guide only in the opposite direction (see Uni-directional guiding). This is controlled by the 'Dec guide mode' control on the'Algorithms'
tab of the Advanced Settings dialog. For example, if the mount tends to drift north overall, restrict guide commands to south-only. This is not an
ideal solution, obviously, but you can still use reasonably long exposures and achieve good guiding results - many imagers choose to use this
approach. If you have an unusual circumstance, such as a mount with no declination control at all, you can set the 'Dec guide mode' choice to
'Off'.

Validating Basic Mount Control - the Star-Cross Test

If you are having repeated problems getting calibration to complete without alert messages, you should run a very simple test to see if the mount is
responding to guide commands. This test basically mimics what is done during calibration, but it is more direct and can give you a better feel for
what's going on. We'll call it the "star-cross" test. The idea is to open the shutter on the main imaging camera, then send guide commands that
should cause the stars in the field to trace out a distinctive cross pattern. In other words, you want to get an image that looks something like this:

The angular orientation doesn't matter, that's just a function of how you have the guide camera rotated. What is important is that the lines in the
cross are perpendicular and have roughly equal lengths in each of the four directions relative to the starting point in the center. If the image you get
doesn't have this approximate appearance, guiding will either be impaired or perhaps impossible. For example, consider the following poor result:

54
You can see the star has moved along only one axis - only in right ascension in this example. The declination guide commands sent to the mount
did nothing at all. Until this is fixed in the mount, you won't be able to guide in declination at all and will have to disable declination guiding to even
complete a calibration. There are many other permutations of bad results, each suggesting a particular problem in the mount, the guide cable, or
much less likely, the ASCOM driver for the mount. You can safely assume it has nothing to do with PHD2.

Here are the steps for running the test:

1. Set the mount guide speed to 1X sidereal. Bring up the 'Manual Guide' tool in PHD2 and choose an initial pulse size - start with, say, 5
seconds.
2. Start a 60 second exposure on the main camera.
3. Send a 5-second pulse west, then two 5-second pulses east, then a final 5-second pulse west. This should return the star to its approximate
starting position. You should wait about 5 seconds after sending each guide pulse to give the command time to complete before sending the
next pulse.
4. Now send a 5 second pulse north, then two 5-second pulses south, then a final 5-second pulse north. This should again return the star to its
starting position.
5. Wait for the main camera image to download and see what you get.
You can use different pulse lengths if you want, perhaps using smaller values to confirm the mount will respond to them. Just be sure the total
exposure time on the main imaging camera is longer than the total of guide durations plus a margin for error. On most mounts, the star will not
return to its exact center because of some declination backlash - you can see that in the first example image. But it should be fairly close or you'll
need to look more carefully at how much declination backlash you have in the mount. PHD2 also has a star-cross test tool, described here: Star-
cross Tool. You can use that to automatically perform the test steps described in 1-5 above.

One benefit to using this test is that it reduces things to the absolute basics: will the mount move as directed or not. It has nothing to do with PHD2
guide settings because they aren't involved in the test. You may find it helpful to use the test results to communicate with the mount manufacturer or
other users who understand your type of mount and its typical problems.

Measuring the Mount's Behavior

If you're having trouble getting decent guiding results, your first instinct will probably be to try making wild changes to the guiding parameters in the
hope of finding a magic solution. This almost never works, and you're more likely to just make things worse. If the default parameters from the
new-profile-wizard aren't producing reasonable results, the fault is probably with the hardware and you'll need to determine the underlying cause.
Once you understand the cause, you can probably improve your guiding results even if no actual repairs can be made - but understanding the
underlying problem is important. To understand what the mount is doing, perform the following steps:

1. Use the new-profile-wizard to create a new equipment profile for the test, being sure the guide scope focal length and camera pixel size
are correct. Don't guess at them, look them up if you aren't sure.
2. Use an ASCOM connection to the mount if one is available and set the mount guide speed to 0.5x - 1x sidereal. Disable any backlash
compensation you have in the mount.
3. Use 1-2 second exposures and let PHD2 auto-select a guide star near Dec=0 with the scope pointing at least 45 degrees above the
horizon to minimize seeing effects.
4. Run the Guiding Assistant for 10-15 minutes and apply whatever recommendations it makes, particularly with respect to min-move
values. Let it measure your declination backlash. You may need to use a large tracking region to avoid losing the guide star during this part
of the process - just be sure there aren't multiple stars in the tracking rectangle. The backlash test will move the star a long distance north,
so choose a guide star that is nearer the southern edge of your camera frame to give yourself plenty of room.
5. Watch how things are going during the GA session. If you bump the mount or something really unusual happens, stop the test and then
restart it. The goal is to measure the performance when things are running normally.
6. Do not change any of the guide parameters beyond what is recommended by the Guiding Assistant.
7. Take a careful look at the results shown in the Guiding Assistant table. Each entry in the table can tell you something useful about the
mount's performance. These results are also written to the guiding log, so they are available for later analysis.
8. If you got calibration alert messages in step 3, you should probably remedy those problems before proceeding. Guiding with a bad
calibration is not likely to produce good results. Also, if your polar alignment error is 10 arc-min or more, you should improve on that and
then repeat the above steps.
9. Let PHD2 guide for another 10-15 minutes, just letting it run as long as there aren't gross errors from wind or other "mistakes." Do
NOT change any of the guiding parameters while this is being done.

If you want to analyze the results yourself, use the PHDLogView tool and the tutorial on Analyzing PHD2 Guiding Results. You should also
consult the document on PHD2 Best Practices. All of these references are available on the OpenPHDGuiding.org web site under the 'News' tab.
If you'd like some help understanding the results, post both the guiding and debug log files on the OpenPHD2 Google forum and we'll be glad to
help you out.

Display Window Problems

New users often complain that the image displayed in the main window is extremely noisy or is almost all-white or all-black. Assuming the camera
is functioning and actually downloading images, the display issues are often caused by the absence of any usable stars in the frame. For example,

55
trying to test the camera indoors or in daylight will almost always create these conditions. The appearance of the image display window in these
situations provides no useful information and should be discounted. PHD2 uses an automatic screen-stretching function that is intended to help you
see real stars under a nighttime sky. When no stars are present, the display will be stretched to show the range of minimum-to-maximum
brightness values of whatever is in the frame - which is often nothing at all. This is usually what causes the noisy/all-white/all-black display results.
You may also encounter display problems if the guider is not well-focused. Focusing the guider can be a tedious process but it's critical to getting
good guiding results. A good technique is to start with a bright but unsaturated star and try to reach focus with that. Then move to successively
fainter stars to fine-tune the focus position using the PHD2 Star Profile tool to measure the size of the guide star. Good results can also be
obtained using a Bahtinov focusing mask or focusing tools in other applications. It doesn't matter what you use so long as you reach a good focus
position.

Hot-pixel and Star-Selection Problems

With most guide cameras, you can encounter problems where clumps of hot pixels are mistaken by PHD2 as guide stars. This can be especially
annoying if you're using automation tools and the 'auto-select' guide star selection is mistakenly choosing hot pixels. For many cameras, a simple
dark frame will suffice for reducing or eliminating hot-pixel problems, and dark frames should always be used as a starting-point. But for other
cameras, you will need to build a bad-pixel map and update it as necessary when you see changes in the locations and sizes of defective pixels.
Camera sensors change over time and may react to changing temperatures, so bad-pixel map maintenance is a small task you should be willing to
perform. Step-by-step instructions can be found in the Bad-pixel map chapter of this document. These problems are different from transient hot
pixels, which can be caused by cosmic ray strikes on the sensor. Although cosmic ray hits can disrupt guiding, there's really little you can do about
them.

Since the recommended practice is to let PHD2 choose the guide star ("auto-select"), you should use the available UI controls to help PHD2 do
the best possible job. The Minimum-HFD property on the Guiding tab of the Advanced Settings dialog is probably the most effective tool for
avoiding hot-pixel selection. You should set its value to allow use of the smallest and faintest real star your setup can produce. You should use the
Star Profile tool to measure a reasonable sample of legitimate guide stars for your system. Then set the Minimum-HFD value to accept those stars
while rejecting smaller bright spots that are really just sensor defects. At the other end of the scale, you should also specify the brightest pixel
value your system will deliver - the ADU value that represents saturation. By doing this, you will prevent PHD2 from rejecting stars that have a
flattened profile but aren't really saturated. The saturation control resides on the Camera tab of the Advanced Settings dialog and is part of a
control group labeled 'Star Saturation Detection'. Choose the option for 'Saturation by Max-ADU value', then set the value for your system. If
you have an 8-bit camera, saturation will be around 255, while a 16-bit camera will saturate around 65000 ADUs. If you don't know the correct
value, you can just point the scope at a bright star, use a multi-second guide camera exposure, and again look at the Star Profile window. One of
the things you'll see in that window is the 'Peak Value' - that's the ADU value for the brightest pixel and the one to use for setting the saturation
point. Using both of these controls is likely to produce much better results for PHD2 guide star selection.

Restoring a Working Baseline

Despite advice to the contrary, you may have made rapid, uninformed changes to your guiding parameters only to find the performance stayed the
same or even got worse. Before proceeding, you should restore the settings to their default values. If you used the new-profile-wizard to build
your profiles, the parameters will have been set based on the specifics of your configuration, and they are likely to be pretty close. If you
encounter significant guiding problems using those settings, you are probably having issues with the mount or other hardware. Blindly changing
guiding parameters almost never solves these problems and quite often makes things worse. You have several options for restoring the settings to
their default values:
1. On the 'Algorithm' tab of the Advanced Settings dialog, you can individually reset parameters by looking at the tool-tip for each field.
Hover your mouse cursor over the field and the default value will be displayed. Note that this is not accurate for the min-move settings,
which depend on your image scale. This approach is best when you want to restore only a few settings.
2. Click the 'reset' buttons on the 'Algorithm' tab for the selected RA and Dec guide algorithms. This is the recommended approach for
resetting all the guiding parameters. The min-move settings will be reset to the values originally calculated by the new-profile-wizard. If you
subsequently adjusted those settings by running the Guiding Assistant, you should repeat that process.
3. Run the new-profile-wizard, accessed by clicking on the 'Manage Profiles' button in the 'Connection' dialog. Use the same camera and
mount choices you already have and give the profile a new name. If you want to re-use the dark library and bad-pixel map from the old
profile, connect to the new profile and use the 'Darks' menu to import those files from the old profile. Once you are satisfied with the new
profile settings, you can delete the old one.

Camera Timeout and Download Problems

In some cases, you may experience problems where guider images aren't downloaded or displayed. In extreme cases, this may even cause PHD2
or other camera-related applications to be non-responsive (i.e. to "hang"). Again, this is almost always due to hardware, camera driver,
or connectivity issues, with one of the most common culprits being a faulty USB cable or device. It is highly unlikely to be caused by an
application like PHD2, so you should begin your investigation at the lower levels of the system. You can start by confirming that the guide camera
is working - try using a short, direct cable from the camera to the computer and taking exposures with the native or test application that came with
the camera. If the camera is functional, you can start looking at USB hubs and cables, swapping them one at a time to see if you can isolate the
problem. It's worth remembering that we work in a hostile environment while doing our imaging, and many of the components we use are not
designed for cold, outdoor conditions. So something that worked just last week or last month may no longer be reliable.

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To help detect and work around these kinds of problems, PHD2 uses a camera timeout mechanism. This timeout value is set in the Camera tab
of Advanced Settings. and uses a default value of 15 seconds. This means that PHD2 will wait up to 15 seconds after the completion of the
exposure to receive the image from the camera. This is a very generous amount of time and should work well for most cameras. However, some
cameras are known to create problems by making large bandwidth or power demands on the USB subsystem. If you are getting timeouts of this
sort and are convinced the camera is working properly, you can increase this timeout value. You can even change it to a very high number - even
1000 seconds or more - so that timeout errors are never shown. Doing so leaves you vulnerable to apparent hangs in the user interface and erratic
guiding behavior, but it is a choice you can make for yourself. A larger value for the timeout will not create extra delays during normal camera
operations - once the image is downloaded from the camera, the timer is cancelled and guiding will proceed immediately.

Here are some diagnostic steps that can help you isolate these kinds of problems:

Common sources of camera timeout problems are the USB subsystem on the host computer, incompatible USB3/USB2 connections, damaged or low-quality USB
cables, or flakey camera drivers. You will probably need to work through a number of scenarios to see what your problem is. Fortunately, this can usually be done in
the daytime by putting the cameras in continuous-exposure mode and letting them run. Start by connecting just the imaging camera and the guiding camera because
these will be the two heaviest users of the USB subsystem. To start, there are often problems when a USB-2 camera is connected to a USB-3 port on your computer.
Those things are supposed to be backward-compatible but that’s only at the hardware level – the driver implementations can be adversely affected. There are two
areas to look at: 1) USB traffic and bandwidth and 2) power delivery to the cameras. Your main imaging camera probably has its own power supply but other devices
like the guide camera may be powered via the USB cable. If that’s the case for you, you may want to try using a powered USB hub to deliver power to the camera.
It’s also best to use high-quality USB cable with a 24AWG power conductor and eliminate long USB cable runs and USB extenders. If your problem seems to be
with USB traffic, there may be other things you can try:
1. Make sure your computer is running from AC power and that the OS can't disable the USB ports for power conservation. Don't run other resource-intensive
applications while trying to image.
2. Bin the guide camera to reduce the size of the downloaded guider images
3. Adjust the USB usage limit of the camera if the camera driver supports that option
4. Use sub-frames in PHD2
5. If you’re running Windows, you can use a Microsoft tool to map out how the various USB ports are tied to the USB controllers in the computer. Then you
can try to isolate the two cameras on separate USB buses.
6. Try using a different camera driver (e.g. an ASCOM driver) if one is available

Poor Guiding Performance

Once you've gotten everything running, you will probably get reasonably good guiding results almost immediately. You will have to decide what
"good enough" means, and everyone's standard is likely to be different. But if you find your imaging results are not acceptable because the stars
are streaked or elongated, you'll need to take a systematic approach to correcting the problems. It is often tempting to just start blindly adjusting
the various guide parameters in an effort to make things better. There is nothing wrong with adjusting the parameters - that's why they're there -
but it should be done carefully based on an understanding of what they do and what problem you're trying to solve. The PHD2 default settings are
carefully chosen to produce reasonable results for most amateur equipment and locations. Optimal settings are entirely dependent on the image
scale, seeing conditions, and behavior of your specific mount. In other words, they are unique to your situation - there is no magic "red book" of
correct guiding parameters, and settings you get from other users may be completely irrelevant to your situation. If you got started by using the
new-profile-wizard, the default settings will already be tuned fairly well to match your image scale. By using the Guiding Assistant, you can get
more specifics about your situation - how the seeing conditions look and how you might adjust the minimum-move settings to avoid chasing the
seeing. You can also use either the Guiding Assistant or the Manual Guiding tool to see how much backlash is present in your mount, something
that can be important to understanding your declination guiding results.

Achieving the best possible guiding performance can be a complex task and not something that can be covered here. However, you can get help
on the web from a variety of sources, with the document by Craig Stark being a very good place to start:
http://www.cloudynights.com/page/articles/cat/fishing-for-photons/what-to-do-when-phd-guiding-isnt-push-here-dummy-r2677.

Alert Messages
PHD2 will sometimes display alert messages at the top of the main display window. These generally show error or diagnostic information that
warrant your attention. During normal operation, you probably won't see any of these, but if you do, this section can help you decide what to do
about them.

Dark-library and Bad-pixel Map Alerts

"Use a Dark Library or a Bad-pixel Map" - using a dark library or bad-pixel map reduces the likelihood that PHD2 will mistakenly identify
hot pixels or some other image defect as a star. If you choose to ignore this message, you'll be vulnerable to situations where PHD2 inadvertently
switches from the guide star to a hot pixel and no longer guides correctly.

Format/geometry mismatches - dark frames and bad-pixel maps must match the format of the sensor in the camera being used. If you've
changed the camera in an existing profile, the existing dark/bpm files will not be usable and you'll see this alert message. To avoid seeing the
message, you should instead create a new profile when you change cameras. You'll still need to shoot new darks or bpms, but you can keep the
old files for use with the original camera. In very unusual circumstances, you may see this message when either the driver or PHD2 code for
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handling the camera has changed. You might also see a format-incompatibility alert message if you have an old dark library that has somehow
accumulated frames with different sensor formats.

In any of these cases, you should rebuild the dark library or bad-pixel map from scratch - more information can be found here: Dark Frames and
Bad-pixel Maps

ASCOM Alerts
When you first connect to a mount, camera, or other ASCOM-controlled device, you may see an alert message saying that a required capability is
not supported by the driver. One example would be lack of support for pulse-guiding by an ASCOM telescope/mount driver, something that can
occur with outdated drivers. In these situations, your only recourse is to update the ASCOM driver. These drivers are generally available from
the ASCOM web site or, in some cases, from the device manufacturer. As a rule, the best practice is to use the latest versions of these drivers so
you don't encounter problems that have already been fixed.

You might also see other alert messages associated with the ASCOM driver for the mount:
1. "PulseGuide command to mount has failed - guiding is likely to be ineffective." This is usually caused by a bug or timing sensitivity in the
ASCOM mount driver, and there is generally no way to know if the guide command was executed properly or not. If you rarely see the
alert and your guiding results are acceptable, you can probably ignore it. Despite the alert condition, PHD2 will continue to issue guide
commands, so you don't need to take any immediate action. If you see the alert frequently, you should send us your debug log so we can
understand the details of the problem and possibly help you describe it to the author of the ASCOM driver.
2. "Guiding stopped: the scope started slewing." This is pretty self-explanatory, but the determination that the scope was slewing is
something reported to PHD2 by the ASCOM mount driver. Whether it was actually slewing isn't known to PHD2. Assuming you didn't
mistakenly slew the scope with guiding active, there is probably a timing problem in the driver. If you want to sidestep the problem
temporarily, you can disable the logic to check for slewing - go into the 'Guiding' tab of the Advanced Settings dialog, and un-check the box
that says "Stop guiding when mount slews." This will let you continue guiding, but the results might be suspect. The debug log should
provide the details needed to describe the problem to the author of the ASCOM driver.

Camera Timeout Alerts

Alert messages associated with camera timing/timeout problems are discussed above: Camera Timeouts

Calibration Alerts
A number of alerts may appear during the mount calibration process. These are described here: Calibration Alerts

Maximum-Duration Limit Alerts

During normal guiding, you may see an alert message saying that your settings for maximum-duration limits in RA or Dec are preventing PHD2
from keeping the guide star locked. If you've decreased these parameters from their default values, you should restore them to their default values.
However, if the limits are well above one second, this alert probably indicates you've encountered a mechanical problem that needs to be
corrected. In the simplest cases, you may have suffered a cable snag, wind gust, mount bump, or other external event that caused the guide star to
move by a large amount. In such cases, you simply need to correct the problem if you can and proceed with guiding. But in other cases, the alert
may be triggered by a steadily growing guide star displacement that is not being corrected at all. For example, if PHD2 can't move the mount
correctly in either the north or south directions, the cumulative uncorrected error will eventually reach a point that triggers the alert. Or you may be
encountering "runaway" Dec guiding because the setting for 'reverse Dec output after meridian flip' (Advanced Settings/Guiding tab) is incorrect.
These sorts of problems will require some diagnosis and simply increasing the maximum-duration limits will not help.

Log Analysis
Any sort of problem isolation or tuning will invariably require use of the PHD2 log files. Both are formatted for straightforward interpretation by a
human reader, and the guide log is constructed to enable easy import into other applications. As mentioned in the 'Tools' section, applications such
as PHDLogViewer or Excel can be used to visualize overall performance, compute performance statistics, and examine time periods when guiding
was problematic. With Excel or similar applications, simply specify that the guide log uses a comma as a column separator.

Guiding Log Contents

The contents of the guiding log will continue to evolve as new capabilities are added. But the basic content is stable, and considerable care is
taken to not "break" applications that parse it. If you wish to analyze the log yourself, the following information will be helpful.

The PHD2 guide log will contain zero or more sequences of calibration and zero or more sequences of guiding. Each of these sections has a
header that provides most of the information about the guiding algorithms being used and the internal parameters used by PHD2 for guiding. At the
start of either a calibration run or a guiding sequence, the last line of the header information defines a set of column headings. The meanings of
those columns are shown below:
Calibration columns:
dx, dy are offsets from the starting position, in pixels, in the camera coordinate system
x, y are the camera x/y coordinates of the guide star at the end of each calibration step
Dist is the total distance moved in the camera coordinate system (dist = sqrt(dx*dx + dy*dy). This is the value used by PHD2 to compute
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 the calibration parameters
Guiding columns:
dx, dy are the same as for calibration - offsets from the "lock position" of the guide star in the camera coordinate system
RARawDistance and DECRawDistance - these are the transforms of dx and dy into the mount coordinates - in other words, they use the
arbitrary angle of the guide camera to map from X/Y on the camera to RA/Dec on the mount
RAGuideDistance and DECGuideDistance - these are the outputs from the various guiding algorithms. The guide algorithms operate on the
"raw" distances and decide how far, if any, the telescope position should be adjusted in each axis. For example, with a "minimum move"
parameter set, the "guide" distances can be zero even when the "raw" distances are non-zero.
RADuration, RADirection, DECDuration, DECDirection - these are the values determined by the two "guide" distances above. The
"durations" are the lengths of the guide pulses, in milliseconds, needed to move the mount by the distances specified by RAGuideDistance
and DECGuideDistance
XStep, YStep - step-adjustment durations for the adaptive optics device if one is being used
StarMass - a brightness measure of the guide star image
SNR - an internal "star-detection ratio" used by PHD2 - essentially a measure of how well the star can be distinguished from the sky
background
ErrorCode - an integer value representing the quality of the guide star measurement:
0 - no error
1 - star is saturated
2 - star has low SNR
3 - star mass is too low for accurate measurement
4 - star has drifted too near the edge of the frame
5 - star mass has changed beyond the specified amount
6 - unexpected error
All distance values are in units of pixels. The header for the guiding section will show the image scale as it is known by PHD2, and that can be
used to scale the pixel distance values into units of arc-seconds if desired.

Problem Reporting
If you encounter application problems that are specific to PHD2, you are encouraged to report them to the open-phd-guiding Google group:
https://groups.google.com/forum/?fromgroups=#!forum/open-phd-guiding. Obviously, the more information you can provide, the more
likely we will be able to resolve the problem. Using the following guidelines will help in that regard:
1. Try to reproduce the problem - if we have a clear set of steps to follow, we are more likely to find a solution quickly. If you can reproduce
it, try to reduce things to the minimum number of steps. Remember, we won't have your hardware or computer environment when we try to
reproduce it ourselves.
2. Try to be complete about describing your configuration - operating system, equipment types, PHD2 version, etc.
3. Attach the PHD2 debug log from the session in which you encountered the problem. You can find the debug log in the PHD2 folder in your
Documents folder. If you can't reproduce the problem, try to estimate the time of day when you first saw it - this could help us find evidence
in the debug log without having to sift through hundreds of lines of output. The 'Upload log files' function on the 'Help' menu can help you
find and upload the log files.

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PHD2 Drift Alignment Tool
The drift align tool in PHD2 can be used to quickly obtain a precise polar alignment of your equatorial mount. The process takes a little bit of
practice, but after doing it a few times, you should be able to obtain an accurate polar alignment in minutes. You can use either a separate guide
scope or the main scope for doing the alignment, whichever is more convenient.

Preparation
Make sure your mount is reasonably level.
Make sure your scope is balanced and ready for guiding.
Try to get your mount's polar axis roughly aligned by using your mount's polar alignment scope if it has one. Otherwise, make sure the
mount's polar axis is pointing towards the pole, and the altitude setting corresponds to your local latitude.
Make sure you can see your computer screen when you are standing at the mount.
Start PHD2 and connect your equipment.
You should be using an up-to-date version of PHD2..
These instructions assume you have an ASCOM connection to your mount so PHD2 knows where your scope is pointing. You can still
drift align without an ASCOM connection, see Note about ASCOM.
Calibrate on any convenient guide star, preferably at a declination within 20 degrees of Dec=0, or reload an accurate calibration if you
have an ASCOM or Indi mount connection. Be sure the calibration is correct for the side-of-pier where you plan to do the alignment. If
you're using an 'on-camera' guiding interface, do a fresh calibration from the side-of-pier where you plan to do the alignment. If the
calibration is not correct for the current side-of-pier, the direction of drift will change and any direction-related notes you made previously
won't be correct.
Make sure your PHD2 settings have the correct values for your guide scope focal length and your guide camera pixel size. (Brain =>
Global tab for focal length, Camera tab for pixel size)

Now you are ready for drift aligning.

Azimuth Alignment
Open the Drift Align Tool:

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You will see a window like this:

Position your scope for the Azimuth axis adjustment. Point near the Meridian and the celestial equator. You can either click the 'Slew' button, or
move the mount manually. Your scope should now be pointing something like this:

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And the Drift Align window will look like this:

Notice we are only a few degrees off the meridian ("Meridian offset"), and close to the equator (small value of Declination.)

You are going to alternate between measuring the error ('Drift'), and adjusting the mount ('Adjust'). The rate of declination drift tells us the amount
of alignment error. Each adjustment will reduce the error, and you repeat the process as many times as you need to get the error close to zero.

Click 'Drift' to start measuring the declination drift. PHD2 will select a guide star and start guiding. After a few moments you should see something
like this:

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Pay particular attention to the Declination trend line (Red). At first the Dec trend line will be jumping up and down, but soon the noise should
"average out" and the slope of the line will become somewhat stable. When that happens you are ready to adjust the mount's Azimuth.

Our goal is to make the Dec trend line "flat" -- neither trending up nor down over time. By adjusting the mount's azimuth, you will change the slope
of the Dec trend line.

If this is your first time adjusting Azimuth, you will not know which way to go--East or West? PHD2 does not know either, so you just have to
guess, and you have a 50-50 chance of getting it right. If you choose correctly, the new drift line will be flatter (less steep, closer to horizontal) If
you choose incorrectly, the drift rate will increase (more steeply downward in the example above.)

Click the 'Adjust' button. PHD2 will stop guiding, and you can make your adjustment. You'll see something like this:

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Slowly turn your mount's Azimuth adjustment, watching the screen and moving the guide star towards the magenta circle. The magenta circle
shows how far the guide star needs to move. The magenta circle is larger when the Dec slope is steeper, and it may initially be so large that it is not
visible on the screen. That's to be expected; if it is not visible, just move the guide star approximately the width of the screen. If you do see the
magenta circle, you should move the guide star to the circle, like this:

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After moving the guide star, click 'Drift' to make another measurement. Before you click 'Drift', it's OK to nudge the mount to re-center the star,
or to find a different star, or to get back closer to the meridian. Also, you can choose your own guide star by clicking on it, or just let PHD2
choose.

After a short time drifting, you will have another Dec trend line. Did it get better (closer to horizontal) or worse (away from horizontal)? Make a
note to yourself in the "Azimuth adjustment notes" area, recording how you adjusted azimuth and which direction the Dec slope moved. You can
use this information next time you drift align so you do not have to guess which way to make the azimuth adjustment. For example, with my setup,
turning the azimuth knob clockwise makes the slope go down. Having the note there reminds me that I need to turn the azimuth knob counter-
clockwise to make the slope go up.

Repeat the measurement and adjustment of the mount until you achieve a good flat horizontal dec trend line, like this:

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Altitude Alignment
Now, you will need to repeat the process for the mount's Altitude adjustment. Click the Altitude button; the Drift tool will now look like this:

Click 'Slew' or manually slew your mount toward the horizon (east or west):

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The exact position is not important, but 23-35 degrees above the horizon works well.

Click 'Drift' to start drifting.

Drift until you have a stable Dec slope. Click Adjust, then turn the mount's Altitude adjustment knob. Use your notes recorded in the "Altitude
adjustment notes" area from a previous session to determine which way to turn the knob to move the slope in the desired direction. For example,
with my setup I turn the altitude knob clockwise to make the slope go "down".
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Just as with the Azimuth adjustment, repeat cycles of Drift and Adjust making the measurements and moving the guide star to the magenta circle.
Again, the goal is to get the dec drift line to be horizontal.

Using Bookmarks
Until you are experienced with drift aligning your particular mount, the 'adjustment' part of the process can be a bit tedious. At first, you'll have to
determine how to adjust a knob on the mount to achieve the desired effect: "how much" and "what direction." To help with this, the PHD2 drift
align tool supports "bookmarks". These are a handy way to record the positions of the guide star before and after you've made an adjustment.
Bookmarks are accessed using the Bookmarks menu, or keyboard shortcuts, as follows:
b : toggle/show bookmarks
Shift-b : set a bookmark at the current guide star position (the "lock position")
Ctrl-b : clear all bookmarks
Ctrl-click somewhere on the image: set a bookmark at that position, or remove the bookmark that's already there
By setting a bookmark before you make a mount adjustment, you can get a clear view of how the adjustment has moved the star on the guide
frame.

Notes about ASCOM

The instructions and screenshots above correspond to what you see in PHD2 with an ASCOM or INDI connection to the mount. There are a
couple of differences if you do not have one of those connections.

Scope position data and slewing functions will not be available - you'll have to slew the scope yourself. Keep in mind, the target
altitude/azimuth positions are only approximate - you don't need to be particularly concerned about accuracy - just get reasonably close
with a good guide star available in the field of view.
The solid magenta circle becomes a dashed-line magenta circle. The dashed magenta circle represents a limit to how far the guide star needs
to move, not the exact distance. We only know that the star should not move past the circle. Rather than moving the star all the way to the
circle, you may want to only move it half-way or so as an initial guess. You can use Bookmarks to keep track of where the guide star was
in each Drift/Adjust iteration.

PHD2 Static Polar Alignment (SPA) Tool

The Static Polar Alignment tool provides two modes of operation. Automated mode requires a mount that can slew under computer control and
report its position. Otherwise manual mode is available for ST-4 type guiding ('On camera', GPUSB, etc) or for mounts that are manually
controlled. The SPA tool selects the most appropriate mode according to your mount's capabilities.

Automated Mode
In the automated mode, PHD2 will slew the telescope as needed to perform the alignment procedure. To do this, PHD2 must be connected to the
mount through either an ASCOM or INDI interface, and the mount must be initialized and ready to perform go-to (slewing) operations. To get
started, perform the following steps:
Connect PHD2 to your camera and to your ASCOM or INDI mount driver
Be sure that PHD2 has already done calibration for this set-up
Manually adjust the mount’s RA axis to point within 5 degrees of the apparent pole, then slew the telescope to point to Dec = +90 or -90.
On a German equatorial mount, it’s best to start with the mount in the counterweight-down orientation, pointing at the pole. Use star
alignment or plate solving to get as close as practical to Dec = +90 or -90 degrees.
During the alignment process the mount will slew 10 degrees west, so make sure there is nothing to obstruct the view or interfere with the
scope’s rotation.

Now open the SPA tool via 'Tools'/'Static Polar Alignment', and the first window will open:

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The PHD2 main display would look like this (southern pole example):

The star map at the top of the SPA window shows the approximate position of the polar stars oriented according to your PHD2 calibration and
mount position. You can adjust the ‘Hour Angle’ control or use the ‘Flip Camera’ option to orient the star map to the main display. To pan the star

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map you can double click the point you want at the center; or click the ‘>’ button to center the selected reference star.
The button to the right of the star map lets you toggle between displaying the star map or instructions for using the SPA tool.
You have the option to use manual control by ticking the ‘Manual Slew’ checkbox. Refer to the instructions below for manual-mode alignment.
Use the star map to select a ‘Reference Star’ on the main PHD2 display. Identify which star you selected with the drop-down list. Don't worry if
you don't get it right; it can be corrected later.
When you are ready to start aligning, click ‘Rotate’. The current position is indicated with a small blue circle on the main display, and the
coordinates are displayed in the status bar. Note that the ‘Rotate’ button has changed to a ‘Stop’ button. If you want to quit or stop the mount
slewing, click the ‘Stop’ button.

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After you click 'Rotate', the mount will slew west in RA in small steps as indicated in the status bar. Once two points have been recorded, the
alignment graphic is overlaid on the PHD2 main display.

If you made a mistake identifying your ‘Reference Star’, select the correct one in the drop-down list.
Now follow the instructions under Using the Polar Alignment Overlay to adjust your mount’s polar alignment.

Manual Mode
If you don’t have a mount driver that supports go-to’s or you want to retain manual control of scope slewing, you can use the manual mode of
operation. To get started, perform the following steps:

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 Connect PHD2 to your camera and to your mount’s guider interface (e.g. ST-4)
Be sure that PHD2 has already done calibration for this set-up
Manually adjust the RA axis to point within 5 degrees of the apparent pole, then manually slew the telescope to point to Dec = +90 or -90.
On a German equatorial mount, it’s best to start with the mount in the counterweight-down orientation, pointing at the pole. Use star
alignment or plate solving to get as close as practical to Dec = +90 or -90 degrees.
During the alignment process you’ll need to slew the mount up to 15 degrees west, so make sure there is nothing to obstruct the view or
interfere with the scope’s rotation.

Now open the SPA tool via 'Tools'/'Static Polar Alignment', and the first window will open:

The star map at the top of the SPA window shows the approximate position of the polar stars oriented according to your PHD2 calibration and
mount position. You can adjust the ‘Hour Angle’ control or use the ‘Flip Camera’ option to orient the star map to the main display. To pan the star
map you can double click the point you want at the center; or click the ‘>’ button to center the selected reference star.
The button to the right of the star map lets you toggle between displaying the star map or instructions for using the SPA tool.
You have the option to use manual control by ticking the ‘Manual Slew’ checkbox. Refer to the instructions below for manual-mode alignment.
Use the star map to select a ‘Reference Star’ on the main PHD2 display. Identify which star you selected with the drop-down list. Don't worry if
you don't get it right, it can be corrected later.

When ready, click ‘Get first position’. The current position is indicated with a small blue circle on the main display, and the coordinates are
displayed in the status bar.

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Slew the mount at least 20 minutes west in RA (RA decreases as you slew west).
Select the same reference star on the main display.
Click ‘Get second position’. The position is marked with another small blue circle and the coordinates are displayed in the status bar.

Slew west another 20+ minutes in RA and select the same star again.
Click ’Get third position’.

After a few moments the alignment graphic is overlaid on the main display. If you made a mistake, select the correct ‘Reference Star’ in the drop
down list. Similarly, if any of your alignment points are suspect, slew the mount to the bad point and click the appropriate button to replace its
coordinates. If you had to slew eastwards then it’s best to overshoot and make your final slew westwards to clear any backlash. Alternatively,
slew westwards to a new position and replace the bad point. The points do not have to be in order.

The corrected alignment graphic updates automatically.

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Follow the instructions in the next section to adjust your mount’s polar alignment.

Using the Polar Alignment Overlay

The polar alignment overlay is placed on the main display once enough alignment points have been collected.

The center of the display is indicated with a grey +.

The Center of Rotation is indicated with a red +.
A magenta circle shows the orbit traced by your reference star.
A green circle shows the desired orbit of your reference star when the polar alignment is accurate.
Yellow circles show the orbits of the other reference stars.
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Within each of the green and yellow orbits, a small circle indicates where the star should be located. A grey line connects your reference star to its
target circle on the green orbit. These positions are dependent on the guide star being correctly identified.
A blue line shows the azimuth correction needed to move the reference star and a red line shows the altitude correction required.

To make the adjustment lines easier to see, the orbits can be shown or hidden with the ‘Show Orbits’ option.
Adjust your altitude and azimuth knobs to move your reference star to its target circle. Adjusting in altitude moves the reference star along the red
line. Adjusting in azimuth moves the reference star along the blue line. As an alternative, you can position three reference stars on their respective
orbits. This is important when using manual mode.
To get the most accurate alignment, adjust the ‘Hour Angle’ till the stars on the main display are all offset by the same amount and direction from
their target circles. Then make your adjustments.
To confirm, you can redo the process. You may need to adjust your declination to keep the polar region centered if you had to make large
adjustments. You may also want to return the mount to the start position if you have limited visibility. When finished, click ‘Close’. If you made
large adjustments you may want to re-calibrate.

PHD2 Polar Drift Alignment Tool

The Polar Drift Alignment tool operates on a similar principle to the original Drift Alignment tool. The difference is that the drift is measured near
the celestial pole to calculate the adjustments needed in both Azimuth and Altitude at the same time. However, it becomes less accurate as the
distance of the drift star from the pole increases. Also, it may take some time for the adjustment to settle so Static Polar Alignment can be faster.
The main advantages of Polar Drift Alignment are that any star can be chosen, the tool only needs to know which hemisphere you're in and it does
not need PHD2 to be calibrated first.
To get started, perform the following steps:
Connect PHD2 to your camera
Manually adjust the mount’s RA axis to point within 5 degrees of the apparent pole, then slew the telescope to point to Dec = +90 or -90.
On a German equatorial mount, it’s best to start with the mount in the counterweight-down orientation, pointing at the pole.
Check that your hemisphere is correctly identified and adjust if necessary
If your camera image is mirrored e.g guide camera on an OAG, tick Mirror image
Select a suitable guide star on the main display
Click the ‘Start’ button to start the drift.

You will soon see a red line appear on the main display. This shows the adjustment needed on the guide star to minimise the drift. At first it will
move around a lot until it settles onto a stable adjustment.
When it has settled, click the ‘Stop’ button. The adjustment will remain on the main display.
Adjust the altitude and azimuth knobs to move the guide star into the red circle at the end of the red line.
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76