JP2568605B2 - Flash control system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control system for a flash device of a camera.

2. Description of the Related Art Conventionally, an external light control method and a TTL light control method are known as light control methods of a flash device in a camera using a silver halide film.

In the external light control method, an external light control sensor is provided in the flash device, and the reflected light from the subject due to the light emission of the flash device is integrated over time and received, and the film sensitivity and the aperture value of the camera previously input to the flash device are used. When the amount of light received reaches the required level, the flash device stops emitting light. This has the advantage that dimming is possible without the need for a special device in the camera. There is a drawback in that it is difficult to perform high-precision dimming because the light receiving angle of the dimming sensor is constant and it is not possible to cope with a change in the angle of view.

In the TTL light control method, the image projected on the film surface illuminated by the flash device is measured by the light receiving element in the camera, and the image is adjusted to the appropriate level determined from the film sensitivity set in advance in the flash device and the aperture value of the camera. When the reflected light arrives, the flash device stops emitting light. There is no parallax, and dimming can be performed for changes in the angle of view, enabling high-precision dimming. Although the dimming method is the mainstream in cameras, the difference in the reflectance of each film causes an error due to the measurement of the weak reflected light from the film, and the influence of the background depends on the position and size of the subject. There is a drawback that an error is caused by receiving.

On the other hand, in addition to the above-mentioned external light control method and TTL light control method, the most basic light control method is the guide number (GN) of the flash device based on distance information obtained from the flash device or the camera side.
O.), a flashmatic light control method (hereinafter referred to as DV light control method) is known in which an aperture value of a camera is determined, and then a flash device is caused to emit light to obtain an appropriate exposure.

This DV dimming method can perform high-precision dimming without being affected by the position and size of the subject and the state of the back of the subject. Depending on distance measurement information obtained from a distance ring or the like at the time of focusing of a lens, a camera using a passive type distance measuring device may cause a large distance measurement error due to subject conditions, and does not indicate an accurate subject distance. In particular, since the error increases as the focal length of the photographing lens becomes shorter and the photographing distance becomes longer, a high-precision distance measuring means is required, which is difficult to realize.

By the way, in recent years, without using a silver halide film, a camera of a method of converting subject light into an electric signal by photoelectric conversion using an image pickup device such as a CCD and recording it on a recording medium such as a magnetic disk (hereinafter referred to as an electronic still camera). ) Is provided, but the dimming accuracy required of such an electronic still camera is higher than that of a camera using a silver halide film because the latitude of an image sensor such as a CCD is narrow.
For example, in a silver halide film (negative), the latitude is ±
In contrast to 5 EV, an electronic still camera requires a dimming accuracy of at least ± 1 EV, depending on the characteristics of the CCD.

[Problem to be Solved by the Invention] In an electronic still camera that requires such high-precision dimming, higher-precision dimming than the external dimming method is possible.
When applying the TTL light control method, as a method to receive the reflected light from the subject, I: Install a half mirror in the shooting optical path and receive the subject light reflected by this half mirror with the light receiving sensor II: There are two types of methods: a method in which light reflected from the imaging surface of the CCD is received by a light receiving sensor.

However, in the case of the method I, the amount of light incident on the image forming surface of the CCD having a half mirror in the photographing optical path is reduced, thereby lowering the photographing sensitivity, and the provision of the half mirror is disadvantageous in terms of space. The problem arises.

In the case of the II method, the CCD imaging surface is originally provided with anti-reflection coating and other measures.
There is a problem that the reflected light from D becomes very weak and dimming itself is difficult.

On the other hand, when the external dimming method is applied to improve the dimming light accuracy, a parallaxless mechanism or a mechanism for controlling the light receiving angle of the light receiving sensor is required, which complicates the flash device.
There is a problem of causing an increase in size.

On the other hand, the dimming accuracy of the electronic still camera is extremely severe compared to the silver halide camera, and the angle of view of the electronic still camera is smaller than that of a camera using a silver halide film, so that a short focal length shooting lens is used. Because of the high frequency, there is a problem in that the application of the DV dimming method is disadvantageous in an electronic still camera in terms of distance measurement accuracy and the like.

Also, for example, AF follows the movement of the subject, that is, the focusing lens continues to move, and in shooting in the release priority AF mode used when taking a certain moment etc., it is released regardless of whether or not it is in focus, In some cases, the camera may be released when the measured distance is not determined.
There is a problem that high-precision dimming in the dimming method cannot be performed and a large dimming error occurs at the time of release.

SUMMARY OF THE INVENTION An object of the present invention is to provide a control system for a flash device that makes use of a DV light control method as much as possible, and performs a light control photographing without failure by performing photographing using an external light control method when shooting in a release priority AF mode. It will not be provided.

[Means and Actions for Solving the Problems] The gist for achieving the object of the present invention is as follows.
Used for cameras that have at least a release priority ranging mode that performs a release operation when the release switch is turned on regardless of whether the focusing mode is in focus or out of focus, in addition to measuring the subject distance by passive ranging method. External dimming control means for directing the reflected light from the subject due to the light emission of the flash light emitting unit to the light receiving means for integrated light reception, and stopping light emission of the flash light emitting unit when an appropriate amount of light is received; Flash control device for determining the aperture value of the camera from the subject distance from the camera and the guide number of the flash light emitting unit and causing the flash light emitting unit to emit light. Dimming area setting means for setting a dimming area that can accommodate a dimming error in the photosensitive means of the camera within a distance measurement error determined according to the focal length and the subject distance In photographing in the release priority ranging mode, the external light control unit is selected, and in a ranging mode other than the release priority ranging mode, the focal length of the photographing lens attached to the camera and the distance measurement unit are determined. Is used as input information, and it is determined whether or not the input information is present in the dimming area set by the dimming area setting means. If the input information is present, the flashmatic dimming control means is selected. And a dimming switching control means for selecting the external dimming control means.

[Embodiment] Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings.

FIG. 1 is a block diagram showing an embodiment in which a flash device control system according to the present invention is applied to an electronic still camera.

In the figure, 1 is a photographing lens, 2 is a quick return mirror (hereinafter referred to as QRM) having a sub-mirror 2a, 3 is a shutter, 4 is an image sensor composed of a CCD, 5 is an image signal processing circuit, 6 is a recording circuit, and 7 is a recording circuit. A control circuit for controlling the camera and the flash device, a lens information detecting means 8 for detecting information of the photographing lens 1 such as distance information and a focal length information of a distance ring of the photographing lens 1, and a reference numeral 9 for auto-focusing of the photographing lens 1 Lens driving means for AF), 10 is a half mirror, 11 is a penta roof prism, 12 is an eyepiece, 13
Is a photometric sensor, 14 is a light emitting part of a flash device, 15 is an external dimming sensor of a flash device, 16 is an AF sensor, 17 is an infrared irradiation member of a flash device, 18 is a focal length of a photographing lens and a subject distance. , A program memory in which a switching curve for switching between a DV dimming area and an external dimming area is stored. 19 is an aperture. When a first release switch SW1 (not shown) is turned on, a photometric sensor is provided via a half mirror 10. When photometry is performed by 13 and distance measurement is started by the AF sensor 16 to drive and control the photographing lens 1 and a second release switch (not shown) is turned on, the shutter 3 is driven and photographing is performed. In the camera of, the AF mode switch is selected, the release is not performed until focus is achieved, the normal AF mode and the release priority described above
Shooting is performed in one of the AF modes.

The dimming operation in the flash device control system configured as described above will be described.

In flash photography, the subject is irradiated with infrared rays by the infrared irradiation member 17, and the infrared reflected light from the subject that has passed through the photographing lens 1 is transmitted to the AF sensor via the sub mirror 2a of the QRM2.
The control circuit 7 determines the lens extension amount, and the lens driving unit 9 extends the lens to the in-focus position.

On the other hand, the focal length of the photographing lens 1 and the distance information of the distance ring at the time of focusing are detected by the lens information detecting means 8, and the control circuit 7 obtains the DV information based on the distance information from the two information and the program memory 18. It is determined whether to perform light control or external light control based on the external light control sensor 15, and thereafter, the light emitting unit 14 of the flash device is caused to emit light, and photographing is performed according to the light control method determined by the control circuit 7.

Here, if it is determined that the shooting is performed by the DV light control method, the aperture value of the shooting lens 1 is determined by dividing the guide number of the light emitting unit 14 of the flash information by the obtained distance information, and the QRM 2 is set to the shooting optical path. When the shutter 3 is fully opened and the shutter 3 is fully opened, the light emitting unit 14 emits light under the above-described conditions, and the image of the subject is exposed on the image sensor 4. The subject image is recorded on a recording medium such as a disk.

Also, if it is determined that the shooting is to be performed by the external light control method, the QRM 2 retreats from the shooting light path, and after the shutter 3 is fully opened, the light emitting unit 14 emits light. The light emission of the light emitting section 14 is stopped when the appropriate amount of light is received by the integrated light reception by the sensor 15, and thereafter, the light is recorded on a magnetic disk or the like in the same manner as described above.

In the present embodiment, the selection between the DV light control method and the external light control method using the program memory 18 is performed when the AF mode is the normal AF mode, and when the AF mode is the release priority AF mode. The external dimming method is selected.

Next, the DV stored in the program memory 18
A switching curve for switching between the light control area and the external light control area will be described.

First, the required AF accuracy when DV dimming is performed based on distance information from the AF system is obtained.

X _{0 for} the distance to the subject and x for the defocus amount on the focus plane
Assuming that ₀ ', the distance to the subject that can be covered by the depth is x, the defocus amount of the focus surface at that time is x', and the focal length of the taking lens is f, the required AF information lx 'is given by Newton's formula. lx ′ = x′−x ₀ ′ = f ² (−1 / x + 1 / x ₀ ) (1)

On the other hand, if you try to keep the dimming accuracy within ± 1EV,
From the inverse square law that the illuminance on the object surface is proportional to one square of the distance, for example, when the object distance is 1 m, the required distance accuracy is: Double precision would be required.

Here, when the permissible limit on the long distance side is substituted into equation (1) as x = 1.414x ₀ (2), lx ′ = f ² (−1 / 1.414x ₀ + 1 / x ₀ ) = 0.293f ² / x ₀ (3), and the required accuracy is stricter than on the short distance side.

Here, suppose that the AF accuracy is 40 μm (lx ′ = 0.
04 mm), the subject distance that satisfies the dimming accuracy ± 1 EV corresponding to the focal length of the taking lens is calculated from Expression (3) as a value shown in the following table.

That is, if the subject distance is within the permissible limits shown in the above table with respect to the focal length of the photographing lens used for photographing, DV dimming that satisfies the dimming accuracy becomes possible.

FIG. 2 is a chart showing this relationship. The horizontal axis represents the focal length, the vertical axis represents the subject distance, the hatched area is the DV light control area, the other areas are the external light control areas, and the boundary between both areas. The switching curve of the dimming method is obtained from the above equation (3), and the values in the above table are plotted in this figure, and this chart is stored in the program memory 18.

In addition, as shown in FIG. 2, the external light control area becomes larger as it is used on the short focal length side. Generally, the external light control precision becomes higher as the subject distance becomes shorter. Since the used shooting is often a short-distance shooting, by performing such switching of the dimming method, high-precision dimming as a whole becomes possible.

FIG. 3 is a block diagram showing an embodiment of a circuit configuration relating to dimming control of the control circuit 7.

In the figure, reference numeral 7a denotes a dimming method determination unit,
From the distance measurement information and the focal length information from the camera, it is determined whether to select the DV dimming method or the external dimming method based on the program memory 18, and the determination result is provided in the viewfinder of the camera or in the camera body. In addition, an image is displayed on an external display member 20 such as an LCD. Reference numeral 7b denotes a DV dimming control unit. When the DV dimming system is selected by the dimming system judging unit 7a, an aperture value (GNO.) From the flash device and an aperture value (GNO. AV) is determined, the drive of the aperture 19 is controlled, and light emission is instructed to the light emitting unit 14 of the flash device.
An external dimming control unit 7c performs an external dimming operation when the external dimming system is selected by the dimming system determining unit 7a.

Next, the operation of the control circuit 7 of this embodiment will be described with reference to the flowchart shown in FIG.

In step (hereinafter abbreviated as S) 1, the first release switch SW1 is turned on. If the AF mode is the normal mode, the process proceeds to S-3, and if the AF mode is the release priority mode, the process proceeds to S-20. The AF operation is started in S-3, the AF operation is performed until focus is achieved in S-4, and the process proceeds to S-5. S-
In step 5, the object distance x at the time of focusing on the focal length f of the photographing lens is read out, and the flow proceeds to S-6.

In S-6, based on the criterion of the dimming method stored in the program memory 18, whether the DV dimming method or the external dimming method is selected from the read focal length f and the subject distance x is determined. Judge, and when the DV dimming method is selected, S
At -7, the DV is displayed on the display member 20 indicating that the dimming method has been selected, and the process proceeds to S-8. When the external dimming method is selected, the external dimming is displayed on the display member 20 at S-9. An indication that the method has been selected is displayed, and the flow advances to S-10.

In S-8, the guide number of the flash device is divided by the subject distance information, DV parameters for determining the aperture value (AV) are set, and the flow advances to S-11.

In step S-11, the second mode is set with the DV dimming method selected.
After the release switch SW2 is turned on and focus is achieved, a release is performed (S-12), and shooting is performed under DV light control at S-13.

When the external dimming method is selected in S-6, the display of the external dimming method is performed on the display member 20 (S-9).
Set the aperture value with -10, and the second release switch with S-11
SW2 is turned on, and after focusing, release is performed (S-1
2) An image is taken under external light control (S-13).

On the other hand, if the AF mode is the release priority mode, S-
At 20, the display member 20 indicates that the external dimming method has been selected, and at S-22, the second release switch SW2
AF operation is performed until is turned on (S-23), and when the second release switch SW2 is turned on, the release (S-12) is performed irrespective of in-focus or out-of-focus, and the external light control method is used. Is performed.

[Effects of the Invention] As described above, according to the present invention, the required adjustment of the photosensitive means of the camera within the ranging error according to the focal length of the taking lens used for photography and the subject distance measured. If the light accuracy is satisfied, select flashmatic dimming, otherwise select external dimming to achieve high-precision dimming without reducing the shooting sensitivity or increasing the size of the device The effect that it can be obtained is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of a flash device control system according to the present invention, FIG. 2 is a diagram showing a switching curve of a dimming region, FIG. 3 is a block diagram showing an embodiment of a control circuit, FIG. FIG. 4 shows a flowchart. DESCRIPTION OF SYMBOLS 1 ... Shooting lens 2 ... Quick return mirror 3 ... Shutter 4 ... Image pickup device 5 ... Image pickup signal processing circuit, 6 ... Recording circuit 7 ... Control circuit 8 ... Lens information detecting means 9 ... Lens Driving means 10 Half mirror 11 Penta roof prism 12 Eyepiece 13 Photometric sensor 14 Light emitting unit 15 External light control sensor 16 AF sensor 17 Infrared radiation member 18 …… Program memory, 19 …… Aperture 20 …… Display member.

Claims (1)

(57) [Claims] 1. A release priority ranging mode in which a subject distance is measured by passive ranging means and a release operation is performed when a release switch is turned on regardless of whether the focusing mode is in focus or out of focus. External light control means for use in a camera having at least an external light control means for directing reflected light from the subject by light emission of the flash light emitting unit to the light receiving means for integrated light reception and stopping light emission of the flash light emitting unit when an appropriate amount of light is received A flashlight control unit for determining an aperture value of a camera based on a subject distance from a distance measuring unit and a guide number of the flash light emitting unit and causing the flash light emitting unit to emit light. A light control area in which a light control error in the photosensitive means of the camera can be accommodated within a distance measurement error determined according to the focal length of the taking lens and the subject distance. In the shooting in the release priority ranging mode, the external light control unit is selected.In the ranging modes other than the release priority ranging mode, the focal length of the photographic lens attached to the camera and The subject distance from the distance measuring unit is used as input information, and it is determined whether or not the input information is present in the dimming region set by the dimming region setting unit, and if it is present, the flashmatic dimming control unit is selected. And a dimming switching control means for selecting the external dimming control means if not present.