JP2016114836A - Focus control device, optical device and focus control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an influence of flicker when concurrently using a phase difference AF and contrast AF.SOLUTION: A focus control device 125 has: luminance change detection means 125 that detects a periodical luminance change of a subject; and control means 125 that performs a phase difference focus control controlling a drive of a focus element 104 on the basis of an amount of defocus, and a contrast focus control controlling the drive of the focus element using a contrast evaluation value. When the luminance change is detected, the control means is configured not to perform the contrast focus control, but to perform the phase difference focus control, or when a prescribed condition about at least one of a focus state of an imaging system, a level of reliability of a phase difference focus detection and the amount of defocus is satisfied, the focus control means is configured to perform the contrast focus control, and when the condition is not satisfied, the control means is configured to perform the phase difference focus control.SELECTED DRAWING: Figure 1

Description

  The present invention relates to focus control in an imaging apparatus such as a digital still camera and a digital video camera, and optical equipment such as an interchangeable lens, and more particularly to focus control using both imaging plane phase difference AF and contrast AF.

  In the imaging plane phase difference AF, a pair of subject images having a shift amount corresponding to the focus state of the imaging system composed of the optical system and the imaging device are placed on the imaging device for imaging the subject image formed by the optical system. Let it form. Then, the defocus amount of the imaging system is obtained from the shift amount (phase difference) of the pair of image signals obtained by photoelectrically converting the pair of subject images by the image sensor, and the drive amount calculated from the defocus amount The focusing state of the imaging system is obtained by moving the focus element only.

  On the other hand, in contrast AF, a high-frequency component is extracted from the output of the image sensor obtained by photoelectrically converting the subject image, and a contrast evaluation value indicating the contrast state of the subject image is acquired. Then, the in-focus state is obtained by moving the focus element to the in-focus position where the contrast evaluation value is maximum (peak).

  In Patent Document 1, the focus lens is moved to the vicinity of the position where the in-focus state is obtained based on the focus detection result obtained by the phase difference AF, and then the contrast AF is performed at high speed and with high accuracy. An imaging device capable of obtaining a focused state is disclosed. Further, in the imaging apparatus of Patent Document 1, when the focus detection result obtained by the phase difference AF is highly reliable, the contrast is obtained after moving the focus lens based on the focus detection result until a closer focus state is obtained. Perform AF. Thereby, the in-focus state can be obtained at higher speed.

JP 2010-256824 A

  However, even if contrast AF is performed after performing phase difference AF as disclosed in Patent Document 1, in the situation where the subject is illuminated by a fluorescent lamp, the effect of flicker generated by the fluorescent lamp causes There is a risk that the in-focus state is erroneously determined even though it is not in the in-focus state. As a result, a focused state cannot be obtained at high speed and with high accuracy.

  The present invention provides a focus control device and an optical apparatus that reduce the influence of flicker and obtain a focused state at high speed and high accuracy when phase difference AF and contrast AF are used together.

  A focus control apparatus according to one aspect of the present invention controls driving of a focus element that is movable in an imaging system that photoelectrically converts a subject image formed by an optical system using an imaging element. The focus control device includes: a first focus detection unit that performs phase difference focus detection for calculating a defocus amount of the imaging system from a phase difference between a pair of image signals generated using an output of the imaging element; , A second focus detection unit that generates a contrast evaluation value corresponding to the contrast of the subject image using the output of the image sensor, a luminance change detection unit that detects a periodic luminance change of the subject, Control means for performing phase difference focus control for controlling drive of the focus element based on the focus amount and contrast focus control for controlling drive of the focus element using the contrast evaluation value. When the brightness change is detected, the control means performs the phase difference focus control without performing the contrast focus control, or the focus state of the imaging system, the reliability of the phase difference focus detection, and the defocus amount. The contrast focus control is performed when a predetermined condition regarding at least one of these is satisfied, and the phase difference focus control is performed when the condition is not satisfied.

  Note that an optical apparatus having the focus control device and at least one of the optical system and the imaging element also constitutes another aspect of the present invention.

  A focus control method according to another aspect of the present invention is a method for controlling driving of a movable focus element in an imaging system in which a subject image formed by an optical system is photoelectrically converted by the imaging element. The focus control method includes a step of performing phase difference focus detection for calculating a defocus amount of an imaging system from a phase difference between a pair of image signals generated by using an output of an image sensor, and imaging according to driving of the focus element. A step of generating a contrast evaluation value corresponding to the contrast of the subject image using the output of the element, a step of detecting a periodic luminance change of the subject, and a phase difference for controlling the driving of the focus element based on the defocus amount And a control step for performing contrast focus control for controlling driving of the focus element using the focus control and the contrast evaluation value. In the control step, when the luminance change is detected, the phase difference focus control is performed without performing the contrast focus control, or the focus state of the imaging system, the reliability of the phase difference focus detection, and the defocus amount. The contrast focus control is performed when a predetermined condition regarding at least one of these is satisfied, and the phase difference focus control is performed when the condition is not satisfied.

  According to another aspect of the present invention, a focus control program causes a computer of an optical device to control driving of a focus element that is movable in an imaging system that photoelectrically converts a subject image formed by the optical system using an imaging element. It is a computer program. The focus control program causes the computer to perform phase difference focus detection that calculates the defocus amount of the imaging system from the phase difference between the pair of image signals generated using the output of the imaging element, and with the driving of the focusing element Phase difference focus control that generates contrast evaluation values corresponding to the contrast of the subject image using the output of the image sensor, detects periodic luminance changes of the subject, and controls the drive of the focus element based on the defocus amount And control processing for performing contrast focus control for controlling driving of the focus element using the contrast evaluation value. When the luminance change is detected, the control processing causes the computer to perform phase difference focus control without performing contrast focus control, or the focus state of the imaging system, the reliability of phase difference focus detection, and The contrast focus control is performed when a predetermined condition regarding at least one of the defocus amounts is satisfied, and the phase difference focus control is performed when the condition is not satisfied.

According to the present invention, it is possible to avoid that the contrast focus control is not accurately performed due to the influence of the periodic luminance change of the subject. Therefore, even if there is such a luminance change, focusing can be performed at high speed and with high accuracy. The state can be obtained.

5 is a flowchart for explaining AF processing in Embodiment 1 of the present invention. 1 is a block diagram illustrating a configuration of an imaging apparatus according to a first embodiment. FIG. 3 is a diagram for explaining a flicker detection method according to the first embodiment. The figure explaining contrast AF. It is a figure explaining the setting of the step width of a lens drive amount. 9 is a flowchart for explaining AF processing in Embodiment 2 of the present invention. 9 is a flowchart for explaining a focus degree calculation process according to the second embodiment. FIG. 10 is a diagram for explaining a peak determination threshold value when flicker is detected in the second embodiment. FIG. 10 is a diagram for explaining a reliability threshold value for phase difference focus detection in the second embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

  In Embodiment 1, a single-lens reflex digital camera in which an interchangeable lens can be attached and detached will be described as an imaging apparatus. FIG. 2 shows the configuration of the single-lens reflex digital camera of this embodiment. The camera includes an interchangeable lens unit 100 and a camera body (optical device) 120. The interchangeable lens unit 100 is detachably connected to the camera body 120 via a mount M indicated by a dotted line in the drawing.

  The interchangeable lens unit 100 includes an imaging optical system including a first lens group 101, a diaphragm / shutter 102, a second lens group 103, and a focus lens group (hereinafter simply referred to as a focus lens) 104 in order from the subject side, and lens control described later. System. The imaging optical system forms a subject image on light from a subject (not shown).

  The first lens group 101 is held movably in the optical axis direction OA of the imaging optical system. The aperture / shutter 102 adjusts the amount of light by changing the aperture diameter, and also functions as a shutter when capturing a still image. The diaphragm / shutter 102 and the second lens group 103 move together in the optical axis direction OA, and perform zooming together with the moving first lens group 101. A focus lens 104 as a focus element moves in the optical axis direction OA to perform focus adjustment.

  The lens control system includes a zoom actuator 111, an aperture shutter actuator 112, a focus actuator 113, a zoom drive circuit 114, an aperture shutter drive circuit 115, a focus drive circuit 116, a lens MPU 117, and a lens memory 118. The zoom actuator 111 moves the first lens group 101 and the second lens group 103 in the optical axis direction OA during zooming. The zoom actuator 111 has a zoom position detector (not shown) that detects the current positions (zoom positions) of the first and second lens groups 101 and 103. The aperture shutter actuator 112 opens and closes the aperture / shutter 102. The focus actuator 113 moves the focus lens 104 in the optical axis direction OA. The focus actuator 113 has a focus position detection unit (not shown) that detects the current position (focus position) of the focus lens 104.

  The zoom drive circuit 114 drives the zoom actuator 111 according to the zoom operation of the user. The shutter drive circuit 115 drives the aperture shutter actuator 112. The focus drive circuit 116 drives the focus actuator 113.

  The lens MPU 117 can communicate with a camera MPU 125 described later through a communication terminal provided on the mount M. The lens MPU 117 controls the zoom driving circuit 114, the shutter driving circuit 115, and the focus driving circuit 116 in accordance with a command from the camera MPU 125. The lens MPU 117 detects the current zoom position and focus position, and notifies the camera MPU 125 of the detected position. The lens memory 118 stores optical information necessary for autofocus (AF), and the lens MPU 117 transmits the optical information to the camera MPU 125 in response to a request from the camera MPU 125.

  The camera body 120 includes an optical low-pass filter 121, an image sensor 122, and a camera control system described later. The optical low-pass filter 121 reduces the false color and moire of the captured image. The image sensor 122 includes a C-MOS sensor and its peripheral circuit, and has a plurality of pixels of m pixels (horizontal direction) × n pixels (vertical direction). The image sensor 122 is configured to be able to output independently from each pixel.

  In addition, the image sensor 122 includes a plurality of pixels that output a phase difference focus detection signal used for performing focus detection calculation by a phase difference detection method. The phase difference focus detection signal is a signal generated by photoelectrically converting a pair of optical images (subject images) whose deviation amounts change according to the focus state of the imaging system including the imaging optical system and the imaging element 122. is there. A pair of image signals corresponding to the pair of optical images is generated using the phase difference focus detection signals.

  As the image sensor 122, a sensor having a plurality of pairs of phase difference focus detection pixels that photoelectrically convert light beams that have passed through different regions of the exit pupil of the imaging optical system, in addition to the plurality of imaging pixels. it can. A pair of image signals can be generated using outputs from a plurality of pairs (or a part thereof) of phase difference focus detection pixels. In addition, as the imaging element 122, each of all pixels has a microlens and a pair of photoelectric conversion units, and a pair of optical images formed by two light beams divided by the microlens are photoelectrically converted by the pair of photoelectric conversion units. In this case, a signal that can generate a pair of image signals may be used. In an image sensor having this configuration, an image pickup pixel signal can be extracted by combining the outputs of a pair of photoelectric conversion units of each pixel.

  The camera control system includes an image sensor driving circuit 123, an image processing circuit 124, a camera MPU 125, a display 126, an operation switch group 127, and a memory 128. The camera control system further includes an imaging surface phase difference focus detection unit (first focus detection unit) 129 and a contrast focus detection unit (second focus detection unit) 130.

  The image sensor drive circuit 123 causes the image sensor 122 to perform a photoelectric conversion operation and a pixel signal read operation, and A / D-converts the read pixel signal and outputs it to the image processing circuit 124 and the camera MPU 125. The image processing circuit 124 performs image processing such as γ conversion and color interpolation on the digital pixel signal to generate an image signal, and further performs processing such as compression on the image signal.

  The camera MPU 125 includes an image sensor driving circuit 123, an image processing circuit 124, a display 126, an operation SW 127, a memory 128, an imaging surface phase difference focus detection unit (hereinafter referred to as phase difference focus detection unit) 129, and a contrast focus detection unit 130. Control. The camera MPU 125 transmits a command or request to the lens MPU 117 and receives optical information of the interchangeable lens unit 100 from the lens MPU 117.

  The camera MPU 125 performs AF processing as focus control processing while controlling the phase difference focus detection unit 129 and the contrast focus detection unit 130. In addition, in the imaging plane phase difference AF performed while controlling the phase difference focus detection unit 129, the camera MPU 125 has reliability of the detection result by the phase difference focus detection unit 129 due to the influence of vignetting when the image height at the focus detection position is high. Therefore, a process for correcting it is also performed. Furthermore, the camera MPU 125 performs an imaging process while controlling the imaging element driving circuit 123 and the image processing circuit 124. The camera MPU 125 includes a ROM 125a that stores a computer program for controlling various operations of the camera body 120, a RAM 125b that stores variables used for various calculations, and an EEPROM 125c that stores parameters used for various controls.

  The display 126 is configured by an LCD or the like, and displays information related to the imaging mode, a preview image generated before recording imaging, a recording image generated by recording imaging, a focus state at the time of focus detection, and the like.

  The operation switch group 127 includes a power switch, a release (imaging trigger) switch, a zoom operation switch, an imaging mode selection switch, and the like. The memory 128 is a flash memory that can be attached to and detached from the camera body 120 and records a recording image.

  The phase difference focus detection unit 129 performs focus detection (phase difference focus detection) by a phase difference method. Specifically, the phase difference focus detection unit 129 performs a correlation operation on a pair of image signals generated using the output from the image sensor 122 to thereby obtain a phase difference that is a shift amount of the pair of image signals. Is calculated. Then, a defocus amount corresponding to the focus state of the imaging system (imaging optical system in this embodiment) is calculated from the phase difference. From the defocus amount, the drive amount of the focus lens 104 that brings the imaging system into focus (phase difference focus drive amount: hereinafter, also simply referred to as the focus drive amount) can be obtained. Note that the in-focus state of the imaging system includes not only a state where the defocus amount is zero but also a state close to zero. That is, it means that the focus state of the imaging system is within a predetermined range (focusing range) that can be regarded as a focused state.

  On the other hand, the contrast focus detection unit 130 performs focus detection (contrast focus detection) by a contrast detection method also called a TVAF method. Specifically, the contrast focus detection unit 130 corresponds to the contrast of the image signal (that is, the subject image) using a high-frequency component or the like in the image signal generated by the image processing circuit 124 using the output of the image sensor 122. A contrast evaluation value (TVAF evaluation value) is generated. This contrast evaluation value is generated every time the focus lens 104 is driven by a predetermined drive amount (hereinafter referred to as an AF pitch amount). The position of the focus lens 104 at which the contrast evaluation value is maximized (peak) is a focus position (hereinafter referred to as a contrast focus position) at which the imaging system is in focus. As will be described in detail later, the AF pitch amount is set to the first pitch amount (first predetermined amount) when the focus lens 104 is away from the contrast focus position. And if it is located in the vicinity of the contrast focus position, it is changed to a second pitch amount (second predetermined amount) smaller than the first pitch amount.

  As described above, the camera body 120 of the present embodiment can perform both the imaging surface phase difference AF (phase difference focus control) and the contrast AF (contrast focus control), and these can be used alone or in combination. The imaging system is brought into focus.

  Next, AF processing performed by the camera MPU 125 will be described with reference to FIG. FIG. 1 is a flowchart showing the contents of AF processing. The camera MPU 125 that is a computer executes this processing according to a focus control program that is a computer program. The camera MPU 125 functions as a luminance change detection unit and a control unit. In FIG. 1, “S” is an abbreviation for a step.

  The camera MPU 125 that has started the AF process in step 100 exposes the image sensor 122 in step 101. Thereby, it is possible to obtain an output signal from the image sensor 122 for acquiring a pair of image signals used for the imaging surface phase difference AF and a contrast evaluation value used for the contrast AF.

  Next, in step 102, the camera MPU 125 causes the contrast focus detection unit 130 to perform contrast focus detection. That is, the contrast focus detection unit 130 is caused to generate a contrast evaluation value while driving (moving) the focus lens 104 via the lens MPU.

  Subsequently, in step 103, the camera MPU 125 causes the phase difference focus detection unit 129 to perform phase difference focus detection. That is, the phase difference focus detection unit 129 generates a pair of image signals, performs a correlation operation on the pair of image signals, calculates the phase difference, and further calculates a defocus amount (hereinafter referred to as a defocus amount). , Referred to as a detected defocus amount).

  Next, the camera MPU 125 calculates the reliability of the phase difference focus detection by the phase difference focus detection unit 129 in step 104. In other words, the reliability of the defocus amount obtained by the phase difference focus detection is calculated. The reliability is obtained based on not only the degree of coincidence of the pair of image signals used for phase difference focus detection but also the contrast of the pair of image signals. Considering the contrast of a pair of image signals, a pair of image signals obtained from a subject having a high contrast can be calculated more accurately than a pair of image signals obtained from a subject having a low contrast. As a result, those phase differences can be calculated with high accuracy.

Specifically, the reliability is obtained as follows.
First, the degree of coincidence between a pair of image signals is obtained as follows. A correlation calculation shown in Expression (1) is performed on a pair of image signals (a1 to an, b1 to bn: n is the number of data) read from the phase difference focus detection pixels, and a correlation amount Corr (l) Is calculated.

In Expression (1), l represents an image shift amount, and the number of data when the image is shifted is limited to n−1. The image shift amount l is an integer, and is a relative shift amount with the data interval of the data string as a unit. When the correlation between the pair of data is the highest, the correlation amount Corr (l) is minimized. Further, using the correlation amount Corr (m) (minimum shift amount m) and the correlation amount calculated at a shift amount close to m, the minimum value Corr ( The shift amount d giving d) is obtained. The matching degree FLVL of the pair of image signals is a value Corr (d) when the correlation is the highest with respect to the correlation amount Corr (l) calculated by the equation (1).

  When the defocus amount is large, the asymmetry between the A image and the B image increases, so that the FLVL is large and the reliability is deteriorated. In general, the FLVL with respect to the defocus amount is calculated to be lower as the lens position is closer to the focus position, and the reliability tends to be higher.

Next, the contrast PB of the pair of image signals is obtained as follows. amax is the maximum value of a1 to an, amin is the minimum value of a1 to an, bmax is the maximum value of b1 to bn, and bmin is the minimum value of b1 to bn. in this case,
PBa = amax−amin (2)
PBb = bmax−bmin (3)
It becomes. The contrast PB of the pair of image signals is set to a smaller value of PBa and PBb calculated by the equations (2) and (3).

  The reliability is calculated by normalizing the matching degree FLVL of the pair of image signals and the contrast PB of the pair of image signals. The higher the FLVL and PB, the higher the reliability.

  Next, in step 105, the camera MPU 125 determines the presence or absence of flicker. The flicker referred to here is a periodic luminance change of the subject caused by a periodic change in luminance of a light source such as a fluorescent lamp that illuminates the subject. A flicker determination method will be described with reference to FIG. 3 showing temporal changes in luminance of an image signal obtained by imaging a subject under a fluorescent lamp. FIG. 3 shows the flicker waveform as a periodic luminance change when the frequency of the power source for lighting the fluorescent lamp is 50 Hz and the flicker generation frequency of the fluorescent lamp is 100 Hz (flicker cycle = about 10 ms). . The camera MPU 125 uses the luminance for flicker determination as a partial image signal in the contrast evaluation range (and the vicinity thereof) that is a focus detection target region in contrast AF among the image signals of the entire shooting screen generated by the image processing circuit 124. Use to measure. The hatched circles shown on the flicker waveform in FIG. 3 indicate the luminance measurement points when the operation cycle of the image sensor 122 corresponding to the frame rate of the image signal is 60 fps (exposure cycle = about 16.7 ms). ing.

  The camera MPU 125 performs flicker determination as follows, for example. First, the camera MPU 125 sets a time sufficiently longer than the exposure cycle of the image sensor 122 as a flicker measurement range, and measures the luminance (hereinafter referred to as measurement luminance) in the partial image signal described above for each exposure cycle. The camera MPU 125 detects the minimum value T11 and the maximum value T12 of the measured luminance in the flicker measurement range, and if the difference between the minimum value T11 and the maximum value T12 is greater than a predetermined flicker determination threshold (predetermined luminance difference), the flicker is detected. It is determined that there is. In order to increase the accuracy of flicker determination, flicker determination may be repeatedly performed in a plurality of flicker measurement ranges, and when flicker presence is determined a predetermined number of times or more, it is finally determined that flicker is present.

  It should be noted that the flicker determination process in step 105 is not performed every time in the next and subsequent routines that are started by returning to step 101 from step 115 described later, but every predetermined routine (that is, every predetermined period). ). Within one predetermined period, the result of the flicker determination performed in the first routine of the period is held.

  Further, the processing in steps 101 to 105 is not necessarily performed after the AF processing is started, and may be performed before the AF processing is started. The method for determining (detecting) the presence or absence of flicker is a method other than the method shown in FIG. 3, for example, a method using the output of a light receiving element that directly receives reflected light from a subject without using an image signal. Also good.

  In step 106, the camera MPU 125 determines whether or not the reliability of the phase difference focus detection calculated in step 104 is higher than the focusable threshold (first reliability). If the focusability threshold is higher than this, the focus lens 104 is driven by the focus drive amount calculated based on the defocus amount obtained by the phase difference focus detection. This is the reliability with which a focus state within the range can be obtained. If the reliability is higher than the focusable threshold value, the process proceeds to step 107.

  In step 107, the camera MPU 125 calculates a driving amount (phase difference focusing driving amount) of the focus lens 104 corresponding to the defocus amount calculated in step 103. In step 108, the camera MPU 125 drives the focus lens 104 by the calculated phase difference focusing drive amount.

  Thereafter, in step 109, the camera MPU 125 exposes the image sensor 122, obtains the phase difference between the pair of image signals again, and obtains the detected defocus amount from the phase difference. In this step, it is determined whether or not the detected defocus amount is within the in-focus range, that is, whether or not an in-focus state is obtained. If the in-focus state is obtained, the camera MPU 125 ends the AF process. If the in-focus state is not obtained, the camera MPU 125 returns to Step 107.

  Here, although the case where it is confirmed in step 109 whether the in-focus state has been obtained after driving the focus lens 104 in step 108 has been described, this confirmation is not necessarily performed. For example, when the in-focus driving amount calculated in step 107 is smaller than a predetermined value, it is possible to omit the confirmation of the in-focus state on the assumption that the detected defocus amount and the in-focus driving amount are small.

  On the other hand, the camera MPU 125 that has determined that the reliability of phase difference focus detection is lower than the focusable threshold value in Step 106 determines whether or not flicker is determined in Step 105 in Step 110.

  If it is not determined that there is flicker (it is determined that there is no flicker), the camera MPU 125 proceeds to step 111 and determines whether or not a peak of the contrast evaluation value has been detected. FIG. 4A shows the relationship between the position (horizontal axis) of the focus lens 104 and the contrast evaluation value (vertical axis) in contrast AF when no flicker occurs. A contrast evaluation value is acquired each time the focus lens 104 is driven by the AF pitch amount from the contrast AF start position T1. The hatched circle indicates the position of the focus lens 104 (hereinafter referred to as the contrast evaluation value acquisition position) from which the contrast evaluation value is acquired before the peak of the contrast evaluation value is detected. As shown in FIG. 4A, the camera MPU 125 switches whether the change in the contrast evaluation value accompanying the driving of the focus lens 104 is switched from an increase to a decrease, and whether or not a decrease equal to or greater than a peak determination threshold that is a predetermined decrease amount has occurred. judge.

  If a peak is detected in step 111, the camera MPU 125 calculates the drive amount of the focus lens 104 for driving the focus lens 104 to the contrast in-focus position where the peak is detected in step 112. Then, in step 113, the camera MPU 125 performs control to drive the focus lens 104 to the contrast in-focus position through the lens MPU 117, and ends the contrast AF and the AF process.

  On the other hand, if no peak is detected in step 111, the camera MPU 125 proceeds to step 114 and calculates the drive amount of the focus lens 104 by a drive amount calculation method described later. The camera MPU 125 performs control to drive the focus lens 104 by the driving amount calculated in step 114 through the lens MPU 117 in step 115, and then returns to step 101.

  If it is determined in step 110 that there is flicker, the camera MPU 125 does not determine whether or not the peak of the contrast evaluation value has been detected (step 111), and in step 114, the focus is calculated by the driving amount calculation method described later. The driving amount of the lens 104 is calculated. The camera MPU 125 performs control to drive the focus lens 104 by the driving amount calculated in step 114 through the lens MPU 117 in step 115, and then returns to step 101.

  Here, the reason why it is not determined whether or not the peak of the contrast evaluation value is detected when it is determined that there is flicker will be described. FIG. 4B shows the relationship between the position of the focus lens 104 (horizontal axis) and the contrast evaluation value (vertical axis) in contrast AF when flicker occurs. A contrast evaluation value is acquired each time the focus lens 104 is driven by the AF pitch amount from the contrast AF start position T1. Hatched circles indicate the contrast evaluation value acquisition positions shown in FIG.

  In general, the contrast evaluation value increases as the contrast, which is the brightness difference of the subject, increases. Further, the higher the luminance of the subject, the higher the contrast and the greater the contrast evaluation value. For this reason, the amount of change in the contrast evaluation value with respect to the driving amount (pitch amount) of the focus lens 104 varies depending on the contrast and luminance of the subject.

  When flicker occurs, the luminance of the image signal periodically changes. Therefore, the contrast evaluation value obtained by driving the focus lens 104 includes the original evaluation value component corresponding to the focus state of the imaging system. Not only changes, but also periodic change components due to flicker are included. In such a case, as shown in FIG. 4B, at the position T6 before the true contrast in-focus position T4, the amount of decrease in the contrast evaluation value that has shifted from increasing to decreasing becomes equal to or greater than the peak determination threshold. Is erroneously determined to have been detected. As a result, a false contrast focus position T5 different from the true contrast focus position T4 is detected as the contrast focus position. That is, even when the focus lens 104 is driven to the false contrast focus position T5, the focus state of the imaging system cannot be obtained.

  In this embodiment, in order to avoid such contrast AF based on detection of the false contrast in-focus position, the peak of the contrast evaluation value is not detected when flicker occurs. That is, imaging plane phase difference AF based on the detected defocus amount obtained by phase difference focus detection in step 103 is performed without performing contrast AF. This is because the imaging surface phase difference AF is less susceptible to flicker because the detection defocus amount is obtained by one exposure of the image sensor 122.

  Next, a method for calculating (setting) the driving amount of the focus lens 104 in step 114 will be described. In the state where the flicker is generated, the focus lens 104 is not driven by contrast AF, but in this step, the first pitch amount or the second pitch amount is set as the drive amount of the focus lens 104 described above.

  FIG. 5 shows the relationship between the first and second pitch amounts and the contrast evaluation value. The horizontal axis indicates the position of the focus lens 104, and the vertical axis indicates the contrast evaluation value. In FIG. 5, a graph connecting white circles shows an example of a change in contrast evaluation value with respect to the driving amount of the focus lens 104 when the subject has high contrast and high luminance. The graph connecting the black circles shows an example of a change in contrast evaluation value with respect to the driving amount of the focus lens 104 when the subject has low contrast and low luminance. White circles and black circles indicate the position of the focus lens 104 from which the contrast evaluation value is acquired.

  When the subject has high contrast and high brightness, the change in contrast evaluation value with respect to the driving amount of the focus lens 104 is large, so the AF pitch amount of the focus lens 104 is set to a second pitch amount R2 smaller than the first pitch amount R1. Set. For example, R2 = 1/2 × R1. Thereby, the position where the contrast evaluation value peaks can be detected with high accuracy.

  On the other hand, when the subject has low contrast and low brightness, the change in the contrast evaluation value with respect to the driving amount of the focus lens 104 is small. For this reason, when the AF pitch amount of the focus lens 104 is set to the narrow second pitch amount R2, a clear change in the contrast evaluation value cannot be detected. In general, the contrast evaluation value includes noise of a signal and noise due to a change in the state of the subject in addition to a contrast component corresponding to the contrast of the subject. For this reason, if the contrast evaluation value itself is low or the change in the contrast evaluation value for each driving of the focus lens 104 is small, there is a possibility that a change not corresponding to the contrast of the subject occurs in the contrast evaluation value due to the influence of the noise. As a result, the focus lens 104 may be driven in a direction different from the true contrast focus position. Therefore, when the subject has low contrast and low brightness, the AF pitch amount of the focus lens 104 is set as the first pitch amount R1, and it is easy to detect a correct change in the contrast evaluation value.

  In this embodiment, the camera MPU 125 determines whether or not the subject has high contrast (and high luminance) in the same manner as the luminance measured for flicker determination described above (and its contrast evaluation range (and its (Near)) using a partial image signal. Specifically, the sum of the output differences of adjacent pixels in the partial image range from which the partial image signal is acquired is calculated as the contrast of the subject. Then, it is determined whether or not the subject has a high contrast depending on whether or not the contrast of the subject is equal to or greater than a predetermined threshold, and the AF pitch amount is set to the second pitch amount and the first pitch amount, respectively.

  More simply, it may be determined whether or not the subject has high contrast based on whether or not the maximum signal value of the partial image signal in the contrast evaluation range (and its vicinity) is equal to or greater than a predetermined threshold value. Furthermore, when a plurality of image signals (captured images) are obtained in advance by a plurality of times of imaging with different positions of the focus lens 104, the sum of squares of the output differences of adjacent pixels in each image signal is predetermined. Whether or not the subject has high contrast may be determined based on whether or not the threshold is exceeded.

  Thus, in step 114, the camera MPU 125 sets the drive amount of the focus lens 104 to the first pitch amount or the second pitch amount.

  According to the present embodiment, in a state where flicker occurs, contrast AF is not performed, and only imaging surface phase difference AF is performed, so that an in-focus state (contrast ratio evaluation value peak) is erroneously detected by contrast AF. Can be prevented. Thereby, the influence of flicker can be reduced, and a focused state can be obtained at high speed and with high accuracy.

  Next, a second embodiment of the present invention will be described. In the first embodiment, contrast AF is not performed when flicker occurs. On the other hand, in the present embodiment, even when flicker occurs, predetermined conditions (being in a focus vicinity state to be described later, low reliability of phase difference focus detection, or small detection defocus amount). When the condition is satisfied, contrast AF is performed.

  The configurations of the camera body and the interchangeable lens unit in the present embodiment are the same as those in the first embodiment, and the same components as those in the first embodiment are denoted by the same reference numerals as in the first embodiment. An AF process performed by the camera MPU 125 will be described. FIG. 6 is a flowchart showing the contents of the AF process. The camera MPU 125 that is a computer executes this processing according to a focus control program that is a computer program. The camera MPU 125 functions as flicker detection means, reliability acquisition means, and control means. In FIG. 6, “S” is an abbreviation for a step.

  Since the processing from step 201 to step 210 is the same as the processing from step 101 to step 110 in the first embodiment (FIG. 1), description thereof is omitted.

  The camera MPU 125 determines whether or not the flicker is determined in step 205 in the camera step 210. If it is determined that there is no flicker (ie, it is determined that there is no flicker), the camera MPU 125 proceeds to step 211 and determines whether a peak of the contrast evaluation value has been detected as in step 111 of the first embodiment. judge.

  On the other hand, if it is determined in step 210 that there is flicker, the camera MPU 125 proceeds to step 214 and uses the contrast evaluation value to determine that the current focus state is in the vicinity of the in-focus state (hereinafter referred to as in-focus state). ) Or not. The camera MPU 125 determines whether or not it is in the in-focus state using a focus degree (hereinafter referred to as PL) calculated by the process shown in the flowchart of FIG.

  In FIG. 7, in step S501, the camera MPU 125 acquires the difference between the maximum value and the minimum value (hereinafter referred to as MMP) of the partial image signal in the contrast evaluation area. By using this MMP, the contrast of the subject within the contrast evaluation range can be estimated to some extent even if it is not in focus.

In step S502, the camera MPU 125 acquires a contrast evaluation value (hereinafter also referred to as EVA). EVA becomes larger as the focus state is approached. In step 503, the camera MPU 125 calculates PL using the following equation using MMP and EVA.
PL (%) = (EVA / MMP) × 100
PL represents the ratio (%) of the current contrast evaluation value to the contrast of the subject. Therefore, the degree of blur of the subject image, in other words, the degree of focus of the imaging system with respect to the subject can be obtained according to the size of PL. The camera MPU 125 determines that the in-focus state is in a case where the in-focus degree is equal to or greater than a predetermined threshold.

  As a different method, an increase amount of the contrast evaluation value with respect to a predetermined drive amount (AF pitch amount) of the focus lens 104 within a predetermined time is calculated as an evaluation value increase rate (change rate). You may determine with an in-focus vicinity state when it is more than a predetermined threshold.

  The camera MPU 125 determined to be in the in-focus state in step 214 proceeds to step 211, and determines whether or not the peak of the contrast evaluation value has been detected. Generally, since the change in the contrast evaluation value increases as the focus state is approached, erroneous detection of a peak is less likely to occur even if the contrast evaluation value varies due to the influence of the luminance change due to flicker. For this reason, in this embodiment, the peak is detected when it is determined that the in-focus state is present. If a peak is detected in step 211, the camera MPU 125 proceeds to step 212 and step 213. Since the processing of step 212 and step 213 is the same as the processing of step 112 and step 113 of the first embodiment, description thereof will be omitted.

  On the other hand, the camera MPU 125 that is determined not to be in the in-focus state at step 214 proceeds to step 215. In step 215, the camera MPU 125 determines whether or not the reliability of phase difference focus detection obtained in step 204 is higher than a defocus usable threshold (second reliability) as a predetermined reliability. If the defocus usable threshold is more reliable than this, the defocus amount detected by phase difference focus detection can be used supplementarily, assuming that the final in-focus state is obtained by contrast AF. It is a reliable level. This defocus usable threshold value is lower in reliability than the focusable threshold value described in step 106 of the first embodiment (used in step 206 in this embodiment).

  If it is determined in step 215 that the reliability is lower than the defocus usable threshold, the camera MPU 125 proceeds to step 211 and determines whether or not the peak of the contrast evaluation value has been detected. This is because if the reliability of phase difference focus detection is low, it cannot be determined whether the focus state is close or not, so that the peak of the contrast evaluation value is detected to avoid the inability to focus as much as possible. .

  If the reliability is higher than the defocus usable threshold value in step 215, the camera MPU 125 proceeds to step 216, and the detected defocus amount obtained in step 203 is equal to or larger than the predetermined defocus amount (or larger than the predetermined defocus amount). It is determined whether or not. If the detected defocus amount is smaller than the predetermined defocus amount, the camera MPU 125 proceeds to step 211 and determines whether or not the peak of the contrast evaluation value has been detected. This is because a state where the detected defocus amount is small can be determined to be close to the focused state, and there is no problem even if peak detection is performed.

  If the detected defocus amount is greater than or equal to the predetermined defocus amount in step 216, the camera MPU 125 proceeds to step 217 without determining whether or not the contrast evaluation value peak has been detected in step 211.

  In step 217, the camera MPU 125 calculates the phase difference focusing drive amount of the focus lens 104 corresponding to the detected defocus amount obtained in step 203. Then, the camera MPU 125 calculates a driving amount that is smaller by a predetermined driving amount than the phase difference focusing driving amount. This predetermined drive amount is set so that the focus lens 104 is positioned sufficiently near to obtain the peak of the contrast evaluation value while driving the focus lens 104 in contrast focus detection that will be performed in the routine after the next time. The The camera MPU 125 may change the predetermined drive amount so as to increase as the defocus amount increases.

  In the next step 218, the camera MPU 125 controls to drive the focus lens 104 by the drive amount calculated in step 217. Thereafter, the camera MPU 125 returns to Step 101.

  In this embodiment, the peak evaluation of the contrast evaluation value (step 211) is performed by satisfying a predetermined condition even when flicker occurs. At this time, the peak determination threshold is set to flicker. It is desirable to make it larger than when not. This makes it possible to avoid erroneous peak detection even if the contrast evaluation value varies due to flicker. This will be described with reference to FIG.

  FIG. 8 shows the relationship between the position of the focus lens 104 (horizontal axis) and the contrast evaluation value (vertical axis) in contrast AF when flicker occurs, compared to FIG. 4B. The peak determination threshold is increased. A contrast evaluation value is acquired each time the focus lens 104 is driven by the AF pitch amount from the contrast AF start position T1. A hatched circle indicates a contrast evaluation value acquisition position.

  In FIG. 8, as in FIG. 4 (b), the contrast evaluation value that has been increased so far has turned to decrease at a position T6 before the true contrast focus position T4. Less than the judgment threshold. For this reason, the drive of the focus lens 104 is continued, and the contrast evaluation value decreases beyond the peak determination threshold at the position T7 beyond the true contrast focus position T4, so that the peak of the contrast evaluation value is detected. . Thereby, erroneous peak detection due to the influence of flicker can be avoided.

  Further, when flicker occurs, the threshold regarding the reliability of phase difference focus detection may be changed from that when flicker does not occur. This will be described with reference to FIG. FIG. 9A shows a focusable threshold value and a defocus usable threshold value, which are threshold values relating to the reliability of phase difference focus detection when flicker does not occur. FIG. 9B shows the focusable threshold value and the defocus usable threshold value when flicker occurs. When flicker occurs, there is a high possibility that a correct in-focus state cannot be obtained by contrast AF. For this reason, as shown in FIG. 9B, the focusable threshold value and the defocus usable threshold value are set lower than in the case where the flicker shown in FIG. It is possible to facilitate the phase difference AF.

  According to the present embodiment, when flicker occurs, contrast AF is performed only when predetermined conditions regarding the focus state at that time, the reliability of phase difference focus detection, and the defocus amount are satisfied, and in other cases Performs imaging plane phase difference AF. By not performing contrast AF when not in the in-focus state, it is possible to prevent erroneous detection of the in-focus state (contrast evaluation value peak) due to the influence of flicker. Further, when the reliability of phase difference focus detection is lower than the defocus usable threshold, it is possible to avoid the inability to focus by performing contrast AF. Further, when the defocus amount is smaller than the predetermined defocus amount, the in-focus state can be obtained at high speed by allowing contrast AF. As described above, it is possible to perform AF processing that achieves both accuracy and speed.

  In the above-described embodiment, a case has been described in which a periodic luminance change of a subject due to flicker of a light source that illuminates the subject has been described. The AF processing described in the above embodiment may be applied.

  In the above embodiment, the focus lens 104 as the focus element is driven in the optical axis direction to perform the focus adjustment. However, the imaging element 122 is driven (moved) in the optical axis direction as the focus element. You may adjust the focus.

In the above embodiment, the case where the camera MPU 125 provided in the lens interchangeable camera body (optical device having an image sensor) 120 performs phase difference and contrast AF has been described. However, the interchangeable lens unit 100 as an optical apparatus having an optical system is provided with first and second focus detection means, luminance change detection means, reliability acquisition means, and control means for performing phase difference and contrast AF. Also good. In addition, a lens-integrated camera (an optical apparatus having an optical system and an image sensor) may be provided with first and second focus detection means, luminance change detection means, reliability acquisition means, and control means.
(Other examples)
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  Each embodiment described above is only a representative example, and various modifications and changes can be made to each embodiment in carrying out the present invention.

100 Imaging Optical System 122 Imaging Device 125 Camera MPU
129 Imaging surface phase difference focus detection unit 130 Contrast focus detection unit

Claims (11)

A focus control device that controls driving of a focus element movable in an imaging system that photoelectrically converts an object image formed by an optical system by an imaging element,
First focus detection means for performing phase difference focus detection for calculating a defocus amount of the imaging system from a phase difference between a pair of image signals generated using the output of the image sensor;
A second focus detection unit configured to generate a contrast evaluation value corresponding to a contrast of the subject image using an output of the image sensor in accordance with driving of the focus element;
A luminance change detecting means for detecting a periodic luminance change of the subject;
Control means for performing phase difference focus control for controlling drive of the focus element based on the defocus amount and contrast focus control for controlling drive of the focus element using the contrast evaluation value;
When the brightness change is detected, the control means
Performing the phase difference focus control without performing the contrast focus control, or
The contrast focus control is performed when a predetermined condition regarding at least one of the focus state of the imaging system, the reliability of the phase difference focus detection and the defocus amount is satisfied, and when the condition is not satisfied, the phase difference is determined. A focus control apparatus that performs focus control.   The focus control apparatus according to claim 1, wherein the predetermined condition is that a focus state of the imaging system is in a predetermined in-focus state.   The control means determines whether or not the imaging system is in the in-focus state, a ratio between a difference between a maximum value and a minimum value of an image signal generated from the output of the imaging element and the contrast evaluation value, or the The focus control apparatus according to claim 2, wherein the determination is performed using a change rate of the contrast evaluation value accompanying the driving of the focus element.   The focus control apparatus according to claim 1, wherein the predetermined condition is that the reliability is lower than the predetermined reliability.   5. The focus control apparatus according to claim 4, wherein when the luminance change is detected, the control unit makes the predetermined reliability lower than when the luminance change is not detected.   The focus control apparatus according to claim 1, wherein the predetermined condition is that the defocus amount is larger than the predetermined defocus amount. The control means includes
The contrast evaluation value change due to the driving of the focus element is changed from increase to decrease, and the peak of the contrast evaluation value is detected by the amount of the decrease being larger than a predetermined decrease amount,
2. The contrast focus control performed when the predetermined condition is satisfied, wherein the predetermined decrease amount is made larger when the luminance change is detected than when the luminance change is not detected. The focus control device according to any one of items 6 to 6.   The focus control apparatus according to claim 1, wherein the luminance change detection unit detects the luminance change from an image signal generated using an output from the image sensor. A focus control device according to any one of claims 1 to 8;
An optical apparatus comprising at least one of the optical system and the imaging device. A focus control method for controlling driving of a focus element movable in an imaging system that photoelectrically converts an object image formed by an optical system by an imaging element,
Performing phase difference focus detection for calculating a defocus amount of the imaging system from a phase difference between a pair of image signals generated using the output of the imaging device;
A step of generating a contrast evaluation value corresponding to a contrast of the subject image using an output of the image sensor in accordance with driving of the focus element;
Detecting a periodic luminance change of the subject;
A control step of performing phase difference focus control for controlling the drive of the focus element based on the defocus amount and contrast focus control for controlling the drive of the focus element using the contrast evaluation value;
In the control step, when the luminance change is detected,
Performing the phase difference focus control without performing the contrast focus control, or
The contrast focus control is performed when a predetermined condition regarding at least one of the focus state of the imaging system, the reliability of the phase difference focus detection and the defocus amount is satisfied, and when the condition is not satisfied, the phase difference is determined. A focus control method characterized by performing focus control. A focus control program as a computer program for controlling a drive of a focus element movable in an imaging system that photoelectrically converts an object image formed by an optical system to a computer of an optical device,
In the computer,
Causing phase difference focus detection to calculate a defocus amount of the imaging system from a phase difference between a pair of image signals generated using the output of the imaging element;
As the focus element is driven, a contrast evaluation value corresponding to the contrast of the subject image is generated using the output of the imaging element,
Lets you detect periodic brightness changes in the subject,
Control processing for performing phase difference focus control for controlling drive of the focus element based on the defocus amount and contrast focus control for controlling drive of the focus element using the contrast evaluation value is performed.
When the brightness change is detected, in the control process, the computer
Causing the phase difference focus control to be performed without performing the contrast focus control, or
The contrast focus control is performed when a predetermined condition regarding at least one of the focus state of the imaging system, the reliability of the phase difference focus detection, and the defocus amount is satisfied, and when the condition is not satisfied, A focus control program for performing phase difference focus control.