JP4639518B2 - Flash control device and camera system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flash control device and a camera system for a camera that controls the flash emission amount to an optimum amount.
[0002]
[Prior art]
Conventionally, a so-called TTL light control method has been used as a control method for a flash light emitter of a single-lens reflex digital camera or a silver salt camera. Among cameras that perform TTL light control, there is a camera that obtains information for main light emission by performing preliminary light emission before the main light emission at the time of shooting, and by measuring reflected light from a subject. In such a camera, information such as the reflectance of the subject can be obtained by measuring the reflected light of the preliminary light emission and performing the calculation before photographing, and the main light emission can be emitted with a more appropriate exposure.
[0003]
In particular, in a digital camera in which a solid-state image sensor such as a CCD is placed at the position of a photographing film, it is difficult to perform TTL light control using the surface of the solid-state image sensor. There is one that calculates the amount of light emission and causes this light emission to be performed with this amount of light emission.
[0004]
For such cameras, preliminary light metering is performed on the light beam diffused by the shutter curtain surface in the mirror-up state, and from this light metering result, the intensity of the main light emission with respect to the amount of preliminary light emission is determined. There is something that calculates whether to emit light. In some cases, the reflected light of preliminary light emission is measured with a photometric element provided in the finder optical system in a mirror-down state, and the intensity of the main light emission is obtained by calculation.
[0005]
Japanese Laid-Open Patent Publication No. 2000-187266 discloses a flash control device that divides and measures reflected light from a subject during preliminary light emission, obtains the reflectance distribution of the subject from the result, and obtains information for main light emission. Yes. In the flash control device described in the above publication, the light emission amount necessary for the main light emission is also determined from the photometry result of the preliminary light emission, and the main light emission is performed by the flash light emitting unit with the required light emission amount as a target.
In such a method in which the light emission amount at the time of shooting is determined in advance based on the photometric output at the time of preliminary light emission, the light measurement accuracy at the time of preliminary light emission directly affects the light emission accuracy at the time of shooting. The accuracy of photometry is very important.
[0006]
[Problems to be solved by the invention]
However, in the above-mentioned apparatus, when the setting of the gain (amplification factor when performing output with respect to the incident light amount) set in the flash metering unit that measures the reflected light from the subject during preliminary light emission is not appropriate However, since the signal generated by the reflected light of the preliminary light emission is too small, there is a problem that it is out of the photometric range of the flash photometry unit and the accuracy of the photometric value cannot be obtained sufficiently.
FIG. 6 is a diagram illustrating an example of the relationship between the amount of received light and the output in the flash photometry unit.
In a region where the amount of received light is small, the output becomes unstable and the accuracy is often lowered as shown in the diagrams A and B. Also, if the output is small, it is likely to be affected by noise and the like, so the accuracy may be lowered in the processing after the output.
[0007]
As a specific example, for example, when the shooting distance is long, the amount of reflected light that returns from the subject to the flash photometry unit during preliminary light emission decreases.
Japanese Laid-Open Patent Publication No. 2000-338569 discloses a method of detecting information related to the photographing distance with an encoder provided in the photographing lens and changing the gain of the flash photometry unit based on this information.
[0008]
However, the shooting distance signal obtained by this method changes the accuracy, the upper limit value and the lower limit value of the signal depending on the design differences of each interchangeable lens, and the difference in focal length is particularly affected. A wide lens with a short focal length has a deeper depth of field and a smaller rotation angle of the distance ring than a lens with a long focal length, so the accuracy of the shooting distance signal is poor and the longest shooting distance signal is short. That is, when the subject is far away, the distance ring rotation angle becomes smaller than the encoder resolution, so the signal is not accurate and only a small value can be output.
Therefore, even if the gain of the flash metering unit described above is adjusted using this signal, especially when using a wide lens, even if the subject is far away, the distance signal can only be recognized as close, so an appropriate gain should be set. There was a problem that the accuracy of the photometric value could not be obtained because it could not be set.
[0009]
In addition, in a lens barrel having a short focal length, since the angle of view is wide, the range that needs to be illuminated with flashlight is widened. In general, the illumination by the flash light emitting portion becomes darker toward the peripheral portion, and the amount of light reflected and returned by the subject decreases. Also from this point of view, in a lens barrel with a short focal length, the signal generated by the reflected light of the preliminary light emission becomes small, deviates from the photometric range of the flash photometry unit, and the accuracy of the photometric value cannot be obtained sufficiently Often occurred.
[0010]
On the other hand, the light metered by the flash metering unit during preliminary light emission includes ambient light other than the flash light (hereinafter, steady light), and therefore the gain set in the flash metering unit is affected by the steady light. Therefore, Japanese Patent Laid-Open No. 2000-338569 described above discloses a technique for reducing the gain when the subject brightness is high (when the ambient light is bright).
However, in the conventional flash control device, when the steady light is very dark, the amount of light reaching the flash metering unit is reduced, so that it is outside the meterable range of the flash metering unit, and the accuracy of the metering value cannot be obtained sufficiently. There was a problem.
[0011]
An object of the present invention, even when the focal length using short photographing lens, the gain of the flash metering unit properly configured, the flash control device capable of accurately metering the reflected light of the preliminary emission Is to provide.
[0012]
[Means for Solving the Problems]
The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected and demonstrated, it is not limited to this. That is, the invention of claim 1 is a flash control device for controlling the flash light emitting section (15) that performs preliminary light emission before the main light emission, and the flash light reflected by the subject during the preliminary light emission is returned to the photographing lens. A flash control device comprising: a flash measurement unit (13) for measuring via a light source; and a gain setting unit (28) for setting a high gain of the flash measurement unit when the focal length of the photographing lens (1) becomes short It is.
[0013]
According to a second aspect of the invention, the flash control device according to claim 1, wherein the gain setting unit (28), the gain of time the focal length is shorter than the predetermined value, the focal length than said predetermined value Further , the flash control device is characterized in that it is higher than the gain when it is long.
The invention according to claim 3 is the flash control device according to claim 1, wherein the gain setting unit increases the gain as the focal length is shorter.
According to a fourth aspect of the present invention, in the flash control device according to any one of the first to third aspects, the flash measurement unit divides a field of view of the photographing lens into a plurality of regions and performs photometry, and the gain setting unit. Is a flash control device characterized in that the gain can be set independently for each of the plurality of regions.
[0014]
According to a fifth aspect of the present invention, in the flash control device according to any one of the first to fourth aspects of the present invention, the flash control device includes a stationary light measurement unit (9) that measures the luminance of the subject by stationary light , and the gain setting unit is The flash control device is characterized in that, when the luminance measured by the stationary light measurement unit is relatively small, a gain of the flash measurement unit is set to be relatively large.
[0016]
The invention of claim 6, a camera system characterized by comprising: a flash control device, wherein the light emitting portion and a flash device having a (15) in any one of claims 1 to 5 It is.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings.
FIG. 1 is a diagram showing an optical system of a flash control device for a camera according to the present invention.
The camera shown in FIG. 1 is a camera in which a flash light emitting device having a flash light emitting unit 15 is detachable from the camera body, and is a so-called digital still camera that converts an image formed on an image sensor 14 into an electric signal and records it. It is.
The light beam that has passed through the photographing lens 1 is bent by the quick return mirror 2 and forms an image on the diffusion screen 3 once. Thereafter, it reaches the eyes of the photographer through the condenser lens 4, the pentaprism 5, and the eyepiece lens 6. On the other hand, a part of the light beam diffused by the diffusing screen 3 is re-imaged on the stationary light photometric unit 9 through the condenser lens 4, the pentaprism 5, the photometric prism 7, and the photometric lens 8.
The stationary light metering unit 9 uses a light receiving element such as SPD (silicon photo diode), for example, and divides the object field into five regions B1 to B5 as shown in FIG. Each photometric value can be output.
[0018]
At the time of shooting, the quick return mirror 2 is flipped up at the same time as the aperture 10 is reduced to a predetermined value. Thereafter, at the time of preliminary light emission by the flash light emitting unit 15, a part of the light beam that is substantially imaged and reflected on the shutter 11 is re-imaged onto the flash photometric unit 13 through the dimming lens 12. During the main light emission by the flash light emitting unit 15, the shutter 11 is opened, and a light beam is imaged on the light receiving surface of the image sensor 14 constituted by, for example, a CCD.
[0019]
The flash metering unit 13 is composed of an SPD, a capacitor for accumulating the photocurrent from the SPD, an amplification amplifier, and the like, and has substantially the same divided shape as the stationary photometry unit 9 as shown in FIG. The regions S1 to S5 correspond to B1 to B5 in FIG. The flash photometry unit 13 multiplies the photocurrent generated in the SPD by a different amplifier gain for each area, and accumulates the amplified current in the integrating capacitor. At the time of reading, the electric charge accumulated in the capacitor corresponding to each area is read out as a voltage value, and is converted into digital data by the A / D converter built in the microcomputer 100 (see FIG. 2) on the camera body side. It is captured.
[0020]
The quick return mirror 2 is a half mirror that transmits part of light, and a part of the transmitted light beam is bent downward in FIG. 1 by the sub mirror 16 and guided to the focus detection unit 17. The focus detection unit 17 detects the focus state for any one of the central regions F1 to F5 of the object scene shown in FIG. 3, and the photographing lens 1 is driven until the focus state is achieved.
[0021]
FIG. 2 is a block diagram showing a signal flow of the flash control device in the present embodiment.
When performing focus adjustment, the focus detection unit 17 detects the focus state, and the lens optical system 26 is driven by the motor of the lens drive unit 24. The lens barrel is provided with an encoder 33 that outputs a signal corresponding to the rotation angle of the distance ring corresponding to the amount of extension. When the lens barrel is in focus, the lens barrel outputs a signal obtained from the rotation angle of the distance ring in that state as a signal corresponding to the distance to the subject. This signal is processed by the microcomputer 25 on the lens side to obtain a shooting distance signal. This photographing distance signal is transmitted to a flash control device (microcomputer) 100 on the camera body side through an electrical contact between the camera body and the lens barrel. In the microcomputer 100 on the camera body side, various calculations and controls are performed.
[0022]
As shown in FIG. 3, the stationary light metering unit 9 is a circuit that measures the stationary light by dividing the object field into five.
The exposure calculation unit 22 includes an output from the steady light metering unit 9, and an open F value, a focal length, an exit pupil position, and the like of a photographing lens stored in a lens microcomputer 25 that is a microprocessor provided in the lens barrel. Based on the lens information and the sensitivity information of the image sensor 14 from the sensitivity setting unit 29, an appropriate exposure value related to the steady light exposure is calculated, and is decomposed into an aperture value and a shutter value and sent to the sequence control unit 20 and the like. Output.
[0023]
When the release signal is input from the release switch 27, the sequence control unit 20 raises the quick return mirror 2 and narrows down the aperture 10, and then instructs the flash light emission unit 15 to perform preliminary light emission. Simultaneously with the control, a series of operations such as issuing a main light emission instruction to the flash light emitting unit 15 again is performed.
[0024]
FIG. 5 is a diagram showing an outline of the sequence of preliminary light emission and main light emission.
The sequence control unit 20 controls the flash photometry unit 13, the flash light emission unit 15, and the like based on signals from the exposure calculation unit 22, the sensitivity setting unit 29, and the like. The sequence control unit 20 causes the gain setting unit 28 to set the amplifier / gain of the flash photometry unit immediately before the preliminary light emission (gain setting 1 in FIG. 5), and then causes the flash light emission unit 15 to use a predetermined small guide number. Preliminary light emission in which light emission (hereinafter referred to as chop light emission) is performed at least once is performed. Then, until the stop signal indicating that the amount of light received by the flash photometry unit 13 has reached a predetermined value is generated or the number of times of chopping light emission reaches a predetermined value, the flash light emission unit 15 continues to perform chopping light emission.
[0025]
While the chopping light emission is continued, the flash photometry unit 13 measures the reflected light from the subject subject to preliminary light emission, and accumulates the generated photocurrent (preliminary light emission integration in FIG. 5). The microcomputer 100 reads the output of the flash photometry unit 13 (read 1 in FIG. 5), performs A / D conversion from the A / D port of the microcomputer 100, and captures it as data. After that, the same gain as that during chopping light emission is set (gain setting 2 in FIG. 5), and the photometry is performed by the flash photometry unit 13 without flashing light in the same accumulation time, thereby accumulating steady light. (Stationary light integration in FIG. 5) is performed. This is because the accumulated value of photocurrent at the time of preliminary light emission includes not only the photocurrent due to flash light but also the amount of photocurrent due to stationary light. This is to obtain a net preliminary light emission accumulation value (only the component due to the flash). Based on this net preliminary light emission accumulated value and the sensitivity of an image sensor such as a CCD or film sensitivity, the number of times of preliminary light emission at the time of shooting is calculated and transmitted to the flash light emitting unit 15 (FIG. 5). Main light emission amount calculation / communication) is performed to perform main light emission. In the main light emission, the flash light emitting unit 15 emits the flash light with the instructed light amount.
[0026]
The gain setting unit 28 is a part that calculates the amplifier gain of the flash photometry unit 13 and sets the gain of the flash photometry unit 13. The flash photometry unit 13 multiplies the photocurrent generated in the SPD by a different amplifier gain for each area, and accumulates the amplified current in the integrating capacitor. At the time of reading, the charge accumulated in the capacitor corresponding to each area (see FIG. 4) is read as a voltage value.
As described above, if the gain is an inappropriate value, the reflected light of the flash cannot be measured with high accuracy. Therefore, it is extremely important to set the gain appropriately. The gain setting is desirably set so that the output obtained by multiplying the expected amount of reflected light of preliminary light emission does not overflow or underflow. For this purpose, gain is adjusted by using some information at the time of photographing.
[0027]
This calculation is performed by the microcomputer 100 on the camera body side. Specifically, the following gain adjustment is performed.
(1) When the aperture value is a small aperture, it is expected that the reflected light entering the flash photometric element is small, so the gain is increased.
(2) Even when the guide number per chop light emission for preliminary light emission is small, the gain is increased accordingly.
(3) When the brightness of the steady light is high, the output of the flash photometry element is expected to saturate early, so the gain is lowered.
(4) During bounce shooting, the reflected light is expected to be small, so the gain is increased.
(5) When the distance to the subject is far, the reflected light is expected to be small, so the gain is high. When the distance is close, the reflected light is expected to be large, and the gain is lowered.
(6) The focal length information is obtained from the lens-side microcomputer 25, and when the focal length is shorter than a certain value, the gain of the flash photometry unit is increased.
(7) When the subject brightness due to the steady light is low, the gain of the flash photometry unit is increased.
The above methods (1) to (5) are methods performed by Japanese Patent Application Laid-Open No. 2000-338569, Japanese Patent Application Laid-Open No. 2001-91989, and the like. ) And (7) will be described.
[0028]
(6) Method As described above, conventionally, the gain of the flash photometry unit 13 is adjusted using an imaging distance signal obtained by detecting the distance ring rotation angle of the lens barrel with an encoder. However, in this case, when the wide lens is used, there is a case where a sufficient gain cannot be obtained because the distance signal can only be recognized as close even if the subject is far away.
Therefore, in the present embodiment, focal length information is obtained from the lens microcomputer 25 on the lens barrel side, and when the focal length is shorter than a certain value, the gain of the flash photometry unit is increased by a certain value.
[0029]
Here, as a method of increasing the gain, the following method can be employed.
A: Judgment is made as to whether or not the focal length is smaller than a predetermined value. If true (when the focal length is small), a calculation such as increasing the gain by a certain value is performed (adopted in this embodiment). .
B: The gain is increased as the focal length is shorter.
What is necessary is just to perform such a calculation with the microcomputer on the camera body side to obtain the gain.
In the case of a zoom lens or the like whose focal length can be changed, a signal corresponding to the zoom position (focal length) set at the time of shooting is obtained from the lens microcomputer 25.
As described above, when the focal length information is obtained from the lens side microcomputer and the focal length is shorter than a certain value, the magnitude of the signal output from the flash photometry unit 13 is increased by increasing the gain of the flash photometry unit. And the reflected light can be measured accurately.
[0030]
Method (7) As described above, the photocurrent accumulation value at the time of preliminary light emission includes the photocurrent accumulation value by the steady light. Naturally, when the subject brightness obtained by the stationary light metering unit 9 is large, the contribution ratio of the photocurrent accumulation value by the stationary light also increases.
On the other hand, when the subject brightness is low, the contribution of the photocurrent accumulation value due to the stationary light can hardly be expected, so the total photocurrent accumulation value is expected to be relatively small. When the accumulated value, that is, the output of the flash metering unit becomes extremely small, the linearity of the output value with respect to the input value is deteriorated, and the accuracy may be lowered.
Therefore, when the subject brightness due to the steady light is small as described above, the accuracy of the flash photometry can be prevented from being deteriorated by increasing the gain of the flash photometry unit.
Also in this method, the gain may be increased by a certain value when the subject brightness obtained by the steady light metering unit 9 is smaller than a predetermined value, or the gain may be increased as the subject brightness decreases. May be. In the present embodiment, the gain is increased by a certain value when the subject brightness obtained by the steady light metering unit 9 is smaller than a predetermined value.
[0031]
(Deformation)
The present invention is not limited to the embodiment described above, and various modifications and changes are possible, and these are also within the equivalent scope of the present invention.
For example, in the present embodiment, an electronic still camera using an image sensor such as a CCD has been described as an example, but the present invention can be similarly applied to a camera that exposes a silver salt film.
[0032]
【The invention's effect】
As described above in detail, according to the present invention, the gain setting unit for setting the gain of the flash measurement unit according to the focal length of the photographing lens is provided. The reflected light of the flash light during preliminary light emission can be measured without deteriorating.
Therefore, it is possible to accurately measure the reflected light of the preliminary light emission, and to perform the main light emission using the result, it is possible to perform flash photography at an appropriate exposure level.
[Brief description of the drawings]
FIG. 1 is a diagram showing an optical system of a flash control device for a camera according to the present invention.
FIG. 2 is a block diagram showing a signal flow of the flash control device in the present embodiment.
FIG. 3 is a diagram showing a division shape and a focus detection unit of the steady light photometry unit 9;
FIG. 4 is a diagram showing an optical system of the flash photometry unit 13 and a divided shape of the photometry area.
FIG. 5 is a diagram showing an outline of a sequence of preliminary light emission and main light emission.
FIG. 6 is a diagram illustrating an example of a relationship between a received light amount and an output in a flash photometry unit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Shooting lens 2 Quick return mirror 3 Diffusion screen 4 Condenser lens 5 Penta prism 6 Eyepiece lens 7 Photometry prism 8 Photometry lens 9 Stationary light photometry part 10 Aperture 11 Shutter 12 Light control lens 13 Flash photometry part 14 Image sensor 15 Flash light Light emitting unit 16 Sub mirror 17 Focus detection unit 22 Exposure calculation unit 24 Lens drive unit 25 Lens microcomputer 26 Lens optical system 27 Release switch 28 Gain setting unit 29 Sensitivity setting unit 100 Microprocessor

Claims (6)

A flash control device for controlling a flash light emitting unit that performs preliminary light emission before main light emission,
A flash measurement unit that measures the flash reflected and returned by the subject during the preliminary light emission through a photographing lens;
A flash control device comprising: a gain setting unit that sets a high gain of the flash measurement unit when a focal length of the photographing lens becomes short . The flash control device according to claim 1,
The gain setting unit is configured to make the gain when the focal length is shorter than a certain value higher than the gain when the focal length is longer than the certain value,
A flash control device. The flash control device according to claim 1,
The flash control device, wherein the gain setting unit increases the gain as the focal length is shorter. In the flash control device according to any one of claims 1 to 3,
The flash measurement unit divides the field of view of the photographing lens into a plurality of areas, and performs photometry.
The flash control device, wherein the gain setting unit can set the gain independently for each of the plurality of regions. In the flash control device according to any one of claims 1 to 4,
A stationary light measuring unit for measuring the luminance of the subject by the stationary light ;
The gain setting unit, when the brightness the ambient light measurement unit is measured is relatively small, flash controller and sets a relatively large gain of the flash measurement unit. The flash control device according to any one of claims 1 to 5,
A camera system comprising: a flash device having the light emitting unit.

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