JP2002333649A - Automatic exposure controller for camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic exposure device for a camera by which useless light emission of a stroboscope is reduced in the case of back light and also appropriate exposure is realized. SOLUTION: A CPU 11 decides whether or not a main object is in a back light state through a main photometric element 21 and a sub photometric element 23, and allows a stroboscope to emit light at the exposing time in the case of deciding that the main object is in the back light state, and it compares a distance to the main object obtained by measuring the distance to the main object through a range-finding circuit 25 with the effective coverage distance of the stroboscope arithmetically calculated based on diaphragm value information set at the exposing time, film sensitivity information and stroboscope guide number information. When the distance to the main object is longer than the effective coverage distance, the CPU 11 inhibits the light emission of the stroboscope and also corrects a difference ΔBv while limiting the luminance of the main object to 2 Bv.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic exposure control device for a camera capable of automatically emitting a strobe in a backlight situation.

[0002]

2. Description of the Related Art There is known a camera having a built-in strobe and a strobe automatic flash mode in a backlight mode in which the strobe is automatically fired at the time of exposure in a backlight state. In general, the backlight is determined to be backlight when the brightness of the surrounding subject surrounding the main subject is higher than the brightness of the main subject at the center of the shooting screen by a predetermined value or more. In this conventional backlight automatic flash emission mode, when the backlight is determined to be backlight, the flash is automatically emitted regardless of the distance to the subject. Therefore, when the main subject is far, the main subject is out of the effective range of the strobe and the amount of light of the strobe is insufficient, so that the light is wasted and underexposure occurs, and the battery is wasted. Was. Also, in the case of a lens shutter type camera, the backlit state has a high brightness as a photometric value, so the aperture at the time of shooting is narrowed down, and the flash automatically fires with a small aperture, so the effective distance of the strobe light is further shortened, and There was a high possibility that the light emission was wasted.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the conventional automatic flash emission at the time of backlighting, and has an automatic exposure apparatus for a camera which reduces unnecessary flash emission at the time of backlighting and enables proper exposure. The purpose is to provide.

[0004]

SUMMARY OF THE INVENTION The present invention, which achieves this object, comprises a backlight determining means for determining whether or not a main subject is in a backlight state, and an automatic strobe upon exposure when the backlight detection means determines that the backlight is in a backlight state. Exposure control means for emitting light and exposing; distance measuring means for measuring the distance to the main subject; effective reach distance of the strobe based on aperture value information, film sensitivity information and strobe light amount information set at the time of exposure Calculation means for calculating the distance, and when the distance to the main subject measured by the distance measurement means is longer than the effective reach calculated by the calculation means, strobe light emission prohibition means for prohibiting strobe light emission is provided. The feature is that. The backlight determining means includes a main subject photometer for measuring the brightness of the main subject, a peripheral subject photometer for measuring the subject brightness around the main subject, a main subject brightness and a peripheral subject measured by the main subject photometer. When the difference from the luminance of the surrounding subject measured by the photometry means is equal to or more than a predetermined value, it is determined that the subject is in the backlight state. The calculating means has an exposure calculating function of calculating an exposure value based on a main subject luminance measured by the main subject photometric means and a peripheral subject luminance measured by the peripheral subject photometric means. When the strobe light emission prohibiting means prohibits the strobe light emission, the exposure value is calculated based on the object luminance obtained by correcting the main object luminance in the positive direction. A long-distance subject photographing mode for correcting the main subject brightness by the predetermined value when the backlight determining means determines that the subject is backlit, and performing an exposure calculation based on the corrected main subject brightness; If the flash prohibition means prohibits the flash from firing during backlight,
An exposure value is calculated based on the subject brightness obtained by correcting the main subject brightness with a second predetermined value larger than the predetermined value. In the automatic exposure control device for a camera according to the present invention, the backlight strobe light emission prohibiting means does not prohibit strobe light emission regardless of the distance to the subject when the luminance of the main subject or the peripheral subject is equal to or less than a predetermined value.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1A is a block diagram showing a main part of an electric circuit of an embodiment in which an automatic exposure control device for a camera of the present invention is applied to a lens shutter type camera having a built-in flash.
(B) is a figure which shows typically the photometry area | region of the embodiment.

This lens shutter camera has a CPU 11 having a control function for controlling the overall operation of the camera and a calculation function for calculating an exposure value, a distance to a subject, and the like.
It has. The CPU 11 operates in a state where the voltage of the battery BATT is boosted by the booster circuit (DC / DC converter) 13 and supplied as a constant voltage. CPU
A drive system 11 is connected to a flash circuit 15 of a built-in flash, a shutter drive circuit 17 for driving a shutter, and a film winding motor drive circuit 19 for winding a film. The strobe circuit 15 is a circuit for emitting light from a built-in strobe having a Fresnel lens, a xenon tube, a reflector, and the like as a light emitting unit. The strobe circuit 15 includes a main capacitor for storing electric charge, a charging circuit for charging the main capacitor, and discharging the main capacitor. The xenon tube is caused to emit light, and a light emission control circuit is provided for stopping light emission. The flash circuit 15 operates upon receiving a control signal from the CPU 11.

In this camera, as photometric means, a main photometric circuit 21c for converting the current output of the main photometric element 21 and the sub-photometric element 23 for measuring the luminance of the main subject into a voltage and outputting the voltage to the CPU 11 as a main subject luminance signal;
A sub-photometric element 23 that measures the luminance around the main subject and a sub-photometric circuit 23c that converts the current output of the sub-photometric element 23 into a voltage and outputs the voltage to the CPU 11 as a peripheral subject luminance signal. FIG. 1A shows the relationship between the photometry area of the main photometry element 21 and the photometry area of the sub-photometry element 23 with respect to the shooting screen. In the illustrated embodiment, the main photometric element 21,
Although the number of the sub-photometric elements 23 is one, each may have a plurality. These CPU 11 and main photometric element 2
1. The main photometric circuit 21c, the sub-photometric element 23, and the sub-photometric circuit 23c constitute a backlight determining means. That is, C
The PU 11 obtains an average subject luminance based on the main subject luminance signals and the peripheral subject luminance signals from the photometric circuits 21c and 23c, and determines whether or not the subject is backlit based on a difference between the main subject luminance signal and the peripheral subject luminance signals. For example, the CPU 11 determines that the backlight is bright when the peripheral subject brightness is higher than the main subject brightness by a predetermined value or more.

Further, the camera has a distance measuring circuit 25 as distance measuring means. The distance measuring circuit 25 includes a distance measuring means using a so-called triangulation method, and outputs a distance measuring signal of the distance measuring means to the CPU 11. In the case of the so-called active method, the distance measuring means includes a light emitting element and a light receiving element. The light receiving element receives the distance measuring light emitted by the light emitting element and reflected by the main subject. The light receiving element receives a position signal according to the light receiving position. C
A configuration for outputting to the PU 11 can be used. CPU1
1 calculates a baseline distance based on the input position signal,
Further, the distance to the main subject is calculated from the baseline distance.
In the case of a passive type, that is, a phase difference method, a pair of subject images obtained by subjecting main subject light to pupil division are respectively received by a line sensor, photoelectrically converted, and a luminance distribution signal of the pair of main subject images is output to the CPU 11. The CPU 11 calculates a pair of main subject image intervals based on the pair of luminance distribution signals, and calculates a distance from the image interval to the subject. In any case, the distance measurement circuit 25 can measure the distance of a subject area included in the main subject in the photometry area of the main photometry element 21. The distance to the subject may be either the subject distance or the shooting distance, and may be any distance from any base point of the camera.

This lens shutter type camera includes a main switch SWMAIN, a photometric switch SWS and a release switch SWR as switches. The main switch is linked with the main switch button and is OFF
When the CPU 11 is in operation, the CPU 11 turns off the power to the strobe circuit 15 and other peripheral circuits and enters a sleep state. become. The photometry switch SWS and the release switch SWR are linked with the shutter button, and the photometry switch SWS is turned on when the shutter button is half-pressed, and the photometry switch SWS is kept on when the shutter button is fully pressed. Release switch SWR is turned on. When the photometry switch SWS is turned on, the CPU 11 executes photometry, distance measurement processing, and the like,
When the release switch SWR is turned on, an exposure process is performed.

[0010] The lens shutter camera is further provided with a combination of a DX section which is brought into contact with a DX code formed on the surface of the patrone of the loaded film and conducts.
DX section group 27 for reading sensitivity, back cover switch SWBACK for detecting whether the back cover is opened or closed, automatic exposure mode setting switch SWAEMO for setting automatic exposure mode
An automatic focus mode setting switch SWAFMODE for setting the automatic focus mode is provided. The CPU 11
By detecting the on / off state of these switches, the following processing and setting are performed. The ISO sensitivity is identified based on the combination of the signal levels of the DX intercept group 27 and the ISO sensitivity is set. Each time the automatic exposure mode setting switch SWAEMODE is turned on, the exposure mode is set to the flash automatic emission mode, the red-eye prevention automatic emission mode, the flash emission inhibition mode, the backlight automatic flash emission mode, and the shutter long second interlocking mode (slow shutter mode). Change and set the mode such as (flash off). Each time the auto focus mode setting switch SWAFMODE is turned on, the normal shooting mode and the distant view shooting mode (strobe light emission inhibition) are alternately selected and set.

Further, the camera is provided with a red lamp 29 for displaying a charging completion state during charging of the built-in flash. The red lamp 29 is usually composed of a light emitting diode, and is provided on the side of the eyepiece frame on the back of the camera body. Although this lens shutter type camera has functions provided in a normal camera, it is not necessary for understanding the present invention, so that illustration and description thereof are omitted.

In the embodiment of the present invention, in the distant view photographing mode, the strobe light emission is prohibited, and when the main subject is backlit, the brightness difference of the main subject is corrected up to a first predetermined value. The first predetermined value is equivalent to 1 Ev in this embodiment. The backlight auto-flash mode is a mode in which the strobe is automatically fired when the main subject is determined to be backlit.In the present embodiment, when the main subject is located farther than the strobe effective distance, the strobe light is emitted. In addition to prohibiting light emission, the main subject luminance is corrected for a luminance difference up to a second predetermined value. The second predetermined value is the first predetermined value.
Is larger (brighter) than the predetermined value, and is equivalent to 2Ev in this embodiment. Also, in the present embodiment, in the backlight strobe light emission mode, even if the main subject is backlit and farther than the effective range of the strobe, the strobe light emission is prohibited if the peripheral subject luminance is lower than a predetermined luminance. do not do.

FIG. 2 is a diagram showing the exposure interlocking range of this camera. In the diagram, the numbers on the left side of the vertical axis represent the aperture value Av and the F number in the apex display, and the horizontal axis represents the shutter speed (second). The downward-sloping line indicates the exposure value Ev in the apex display, and the coordinates on the downward-sloping line indicate a combination of the aperture value Av and the shutter speed Tv that is the exposure value Ev. If the exposure value determined by the aperture and the shutter speed is Evs, Evs = Av + Tv = log ₂ (Fno × T) ² .

In FIG. 2, the number on the vertical axis on the right side is the effective reach distance (m) of the built-in strobe light at the aperture value Av, that is, the distance of the subject to which effective strobe irradiation is possible. The built-in strobe of this embodiment is an ISO
At 100, the guide number Gno is 11, and the apex display value Gv is 7. Below, film sensitivity is ISO
The case of 100 will be described. The strobe reach distance (m) is determined by F corresponding to the guide number Gno of the strobe and the aperture value Av set based on the set exposure value Ev.
The value is determined by the number Fno, and is determined by the expression Gno / Fno.

In the lens shutter of this camera, the aperture interlocking range is 5 to 9 for the aperture value Av of the apex display, and F5.6 to F22 for the F number. The shutter speed interlocking range is on the low speed side for convenience of illustration. Is 1/16 second, the high-speed side is 1/300 second, and the shutter speed Tv for Apex display is 4 to 8 + ／. A solid line FM1 is a program line of this camera. The interlocking range by the flashmatic method (FM interlocking range)
The area is above and above M1.

In FIG. 2, a broken line FM2 indicates the limit of the effective reach distance of the strobe light, and a region below the broken line FM2 is a strobe light emission prohibition region for prohibiting the strobe light emission because the subject is too far away. Is shown. In the present embodiment, a case where the subject distance measured by a distance equal to or more than 1 Ev from the effective stroboscopic limit distance determined by the aperture value set according to the subject luminance is defined as the stroboscopic reach distance boundary FM2.

The present embodiment is characterized in that, in the flash emission prohibited area, an exposure correction larger than a distant view exposure correction is performed in order to compensate for a decrease in the exposure amount due to the flash emission inhibition.

In the normal automatic light emission mode of the camera, that is, in the automatic light emission mode at low brightness, when the shutter speed becomes slower than a predetermined value, a strobe is automatically emitted by a flashmatic method to prevent camera shake. Let it. In this embodiment, when the shutter speed (1 / T) is about 1/40 second and the exposure value Evsf1 is 10.5, the built-in flash is automatically fired when the shutter speed becomes slower than this. .

Next, the main operation of the camera will be described with reference to flowcharts shown in FIGS. FIG. 3 shows the main processing of the camera. This process is executed with the battery BATT loaded.

"Main Process" When the "power switch off" main process starts, it is checked whether the power switch is on or off (S1).
01). If it is off, the red lamp 29 is turned off, the strobe circuit 15 stops charging, the power supply to other peripheral devices is cut off, and the mode shifts to the low power consumption mode (S
101; OFF, S103, S105, S107). In the low power consumption mode, the CPU 11 itself is in an operable state by a low-speed clock, and is repeatedly activated to repeat the process of checking the power switch state.

"Power switch on" When the power switch is turned on (S101; ON), it is checked whether both the photometry switch SWS and the release switch SWR are off (S109). If both are OFF, the flash circuit 15 starts flash charging, and also turns on the power supplies of other peripheral circuits (S109; OF)
F, S111). Then, it is checked whether or not the flash circuit 15 is fully charged (S113), and if not, the process returns to S101 (S113; N, S10).
1) If fully charged, the red lamp 29 is turned off, the charging process of the flash circuit 15 is stopped, and the process returns to S101 (S113; Y, S115, S117, S101). In other words, while the power switch is ON, strobe charging is continued and a fully charged state is maintained.

"Photometry switch SWS on" When the photometry switch SWS is turned on (S109; SWS ON), the charging process of the strobe is stopped (S119), the photometry is performed, and the main subject luminance and the peripheral subject luminance signal are input (S121). Then, the distance is measured to calculate the subject distance (S123). Further, the backlight is determined (S129), and exposure calculation is performed (S131).

"When the strobe is fired" Next, whether the strobe is fired is set to "1" in the strobe light emission flag.
Is set (S133). The strobe light emission flag is set to "1" in addition to the strobe forced light emission mode, and when it is determined that the backlight is backlit in the backlight automatic light emission mode, the exposure value Ev is set to the light emission switching reference Ev value in the strobe automatic light emission mode. This is the case when:

When the strobe light is to be emitted (S133;
Y), the red lamp 29 is turned on and off at the first cycle (4 Hz) (S135), and it is checked whether or not full charging is started after the strobe charging is started (S137, S139). When the red lamp 29 blinks in the first cycle, the photographer can recognize that the battery is being charged. If the battery is not fully charged, it is checked whether the photometric switch SWS is ON (S1).
39; N, S141), and if the photometry switch SWS is ON, the process returns to S137 to continue strobe charging (S141; ON, S137).

If the battery is fully charged (S139; Y),
The red lamp 29 is lit (continuously lit) to indicate that strobe charging has been completed.
9 (S143, S145, S149). Then, the state of the photometric switch SWS and the release switch SWR are checked (S149). If the photometric switch SWS is turned off in the check of S141, S
101 (S141; OFF, S101), and if the power switch SWMAIN is ON, S101 to S101
By the process of 113, the strobe is fully charged while the flashing of the red lamp 29 is continued, and when fully charged, the strobe charging is terminated by turning off the red lamp 29 (S1).
13; Y, S115, S117).

While the photometric switch SWS is ON,
Wait for the release switch SWR to be turned on (S14
9; SWS ON & SWR OFF). Photometry switch SWS is off
Then, the red lamp 29 is turned off and the process returns to S101 (S149: SWS OFF, S151, S101). When the red lamp 29 goes out, the photographer knows that the strobe does not emit light.

[Exposure processing] Release switch SWR is set to O
If N, the red lamp 29 is turned off (S149; SWR
& SWS ON, S153). Then, it is checked whether or not the flash is used (S155). If the flash is used, the flash is emitted according to the exposure value of the flash and the exposure operation is performed (S155; Y, S157), and the film is wound up (S161). ), And returns to S101.

When the strobe is not fired (S133;
N), after turning off the red lamp 29, the photometric switch S
The state of WS and the release switch SWR are checked (S147, S149). And release switch S
When the WR is turned on (S149: SWS & SWR ON), the red lamp 29 is turned off, the exposure operation is performed without firing the flash at the exposure value at which the flash is not fired, the film is wound up, and the process returns to S101 (S153, S155). N, S
159, S161 and S101).

[Backlight Determination Processing] Next, the backlight determination processing executed in S129 will be described in detail with reference to the flowchart shown in FIG. In the backlight determination process, first, a brightness difference ΔBv between the main subject brightness Bv_main and the surrounding subject brightness Bv_sub is obtained (S20).
1). Then, it is checked whether or not the brightness difference ΔBv is equal to or more than a predetermined value 1Ev (S203). That is, in the present embodiment, when the luminance difference ΔBv is equal to or more than 1 Ev, it is determined that the light is backlight, and when it is not equal to or more than 1 Ev, it is not determined that the light is backlight.
When the brightness difference ΔBv is equal to or greater than 1 Ev (when the surrounding subject brightness Bv_sub is higher (bright) by 1 Ev or more), “1” is set in the strobe light emission flag and S2 is performed.
The process proceeds to S11 (S203; Y, S205, S211). If the brightness difference ΔBv is not equal to or more than 1 Ev, the brightness difference ΔBv is rewritten to 0, the flash light emission flag is set to “0”, and S
Go to 211 (S203; N, S207, S209, S
211). That is, when it is determined that the subject is backlit, "1" is set in the strobe light emission flag to enable strobe light emission during exposure.

In S211, it is checked whether or not the distance measurement value of the main subject is equal to or longer than the strobe reach distance. The strobe reach distance (m) is a value determined by a strobe guide number Gno corresponding to the ISO sensitivity and an F number Fno corresponding to the aperture value Av set based on the set exposure value Ev, and is expressed by the following equation. It is required by Fno.

"When the backlight is back and the distance measurement value is not longer than the strobe reach distance" When the distance of the measured main subject is not equal to or longer than the strobe reach distance (S211; N), it is not in the distant view photographing mode (S213; N). Under the condition that the lid is not opened and there is no film (S215; N), 1Bv is set as a predetermined value to a limit correction value ΔBvlimit for exposure correction (S217). And
It is compared whether the brightness difference ΔBv is larger than the limit correction value ΔBvlimit (S223). If the brightness difference ΔBv is larger, the brightness difference ΔBv is set to the limit correction value ΔBvli.
Rewrite with the value of mit and proceed to S227 (S223;
If the luminance difference ΔBv is not larger, the process directly proceeds to S227 (S223; N, S2).
27).

In S227, the peripheral subject luminance Bv_su
A value obtained by subtracting the brightness difference ΔBv from b is set as the subject brightness Bv. Then, the subject brightness Bv becomes the minimum brightness Bv.
It is determined whether or not the brightness is less than min. If not, the process returns as it is (S229; N). If the brightness is less than 3, the subject brightness Bv is rewritten with the value of the minimum brightness Bvmin, and the process returns (S229; Y, S231). ). By the above processing, when the subject is backlit and the distance to the subject is less than the strobe reach distance, the brightness obtained by subtracting the brightness difference Bv (maximum 1 Ev) from the surrounding subject brightness Bv_sub is set as the subject brightness Bv, and the strobe light is emitted.

"When the backlight is back and the distance measurement value is equal to or longer than the strobe reach distance" When the distance measurement value is equal to or longer than the strobe reach distance, the proper exposure value is not obtained even when the strobe is fired. Therefore, if the distance measurement value is equal to or longer than the strobe reach distance, the strobe light emission flag is set to "0" to inhibit strobe light emission (S
211; Y, S219). Then, the limit correction value ΔB
The second predetermined value 2Ev is set in vlimit, and the process proceeds to S223 (S221, S223). That is, when the subject is located farther than the strobe reach distance, the limit correction value ΔBvlimit is set to a value twice the normal first predetermined value. Also, if the back cover is opened or there is no film (S215; Y), the flash light emission flag is set to "0" (S219), and the limit correction value ΔBvlimit is set to 2Bv, and S223.
(S221, S223).

The brightness difference ΔBv is equal to the limit correction value Δ
Bvlimit is compared (S22).
3) If the brightness difference ΔBv is larger, the brightness difference ΔBv is rewritten with the value of the limit correction value ΔBvlimit, and S22
7 (S223; Y, S225, S227), and if the luminance difference ΔBv is not larger, the process directly proceeds to S227 (S223; N, S227).

In S227, the peripheral subject brightness Bv_su
The value obtained by subtracting the brightness difference ΔBv from b is set as the subject brightness Bv. Then, the subject brightness Bv becomes the minimum brightness Bvm.
It is determined whether the value is less than "in". If the value is not less, the process returns as it is (S229; N). If the value is less than "in", the object brightness Bv is rewritten with the value of the minimum brightness Bvmin and set (S229; Y, S231). ). According to the above processing, when the subject is backlit and the distance to the subject is equal to or longer than the strobe reaching distance, the strobe is not fired and the surrounding subject brightness B
The luminance obtained by subtracting the luminance difference Bv (maximum 2Ev) from v_sub, that is, the luminance corrected so that the exposure becomes positive is set as the subject luminance Bv.

In the present embodiment, regardless of whether the subject is backlit or the distance measurement value is less than the strobe reach distance,
When the distant view shooting mode is set (S213;
Y), if the back cover is not closed or a film is not loaded (S215; Y), the flash light emission flag is set to "0" in S219, so that no flash light is emitted. In this case, the limit correction value ΔBvlim
2Bv is set in it (S221).

[Exposure Calculation Processing] Next, the exposure calculation processing executed in S131 will be described in detail with reference to FIG. When the calculation process starts, first, the DX intercept group 27
Is converted into a film speed Sv of the apex display (S301),
An appropriate exposure value Ev is obtained from v and the subject brightness Bv measured (S303). Next, it is checked whether or not the photographing mode is the strobe light emission auto (S305).

"In the case of auto flash emission" In the shooting mode of the flash emission auto, for example, in the case of the automatic flash emission mode or the automatic flash emission mode in the backlight, when the shooting mode is auto, the exposure value Ev is the emission switching value Ev_.
It is checked whether it is f1 or less (S305; Y, S3)
07). The light-emission switching reference value Ev_f1 is a light-emission switching reference value E that is a boundary value between whether or not to emit a strobe.
v in the present embodiment, as shown in FIG.
0.5. When the light emission switching reference value Ev_f1 or less,
"1" is set to a strobe light emission flag for strobe light emission, and the process proceeds to S311 (S307; Y, S309, S
311) When the light emission switching reference value Ev_f1 is not less than or equal to:
Skip S309 and proceed to S309 (S307;
N, S311).

In S311, it is checked whether the set exposure value Ev is equal to or less than the minimum exposure value Ev_min_a. Here, the minimum exposure value Ev_min_a is the lower limit exposure value E in the flash automatic flash mode and the flash forced flash mode.
v. In this embodiment, the shutter speed Tv at the time of the minimum exposure value Ev_min_a in the ISO 100 is 1 /
16 seconds. The set exposure value Ev is the minimum exposure value Ev_mi
If n_a or less, set the exposure value Ev to the minimum exposure value Ev_
rewritten to the value of min_a and proceeds to S323 (S31
1; Y, S313, S323), otherwise, the process directly proceeds to S323 (S311; N, S323).

In S323, it is checked whether or not the set exposure value Ev is equal to or more than the upper limit exposure value Ev_max. If it is above, the set exposure value Ev is rewritten with the upper limit exposure value Ev_max, and the process returns (S323; Y, S325). If not, the process returns (S323; N).
The processing of S323 and S325 is processing for limiting the upper limit of the exposure value Ev.

"In the case of flash forced light emission mode" If the flash light emission mode is not auto, it is checked whether or not the shooting mode is the forced light emission mode (S305; N, S315).
In the case of the forced light emission mode, the process proceeds to S309 (S315;
Y), and the process proceeds to S323 via the processes of S309 to S313.

"When neither flash auto mode nor forced flash mode is used"
305; N, S315; N), the flash light emission flag is set to "0" (S317), and it is checked whether the set exposure value Ev is equal to or less than the lower limit exposure value Ev_mins in the light emission prohibition mode (S319). Lower limit exposure value Ev_m
Ins is an exposure value Ev determined by the open aperture value of the camera and the maximum shutter time. In this embodiment, I
The shutter speed Tv at the time of the lower limit exposure value Ev_mins in SO100 is 2 seconds. If the set exposure value Ev is equal to or smaller than the lower limit exposure value Ev_mins, the set exposure value Ev is rewritten with the lower limit exposure value Ev_mins, and the process proceeds to S323 (S3).
19; Y, S321, S323), otherwise, the process directly proceeds to S323 (S319; N, S323). S
Steps 319 and S321 are processing for limiting the lower limit of the set exposure value Ev. When the process proceeds to S323, S323, S325
Then, the process returns. If the mode is not the flash auto mode or the forced flash mode, flash firing is prohibited. For example, there is a shutter long time interlock mode.

According to the above-mentioned embodiment of the present invention, in the automatic flash light emission mode at the time of backlight, if the distance of the main subject is longer than the effective distance of reaching the flash light when the backlight is determined, the flash emission is prohibited. Useless strobe light is eliminated, and battery consumption can be prevented. Further, when the strobe light emission is prohibited, the exposure is corrected in accordance with the luminance of the main subject, so that the main subject can be properly exposed. Further, in the embodiment of the present invention, if the subject brightness is lower than the predetermined value even if it is determined that the subject is backlit, the flash is emitted without prohibiting the flash regardless of the distance to the subject. It will not be misunderstood.

Although the present invention has been described based on the embodiment applied to a lens shutter type camera with a built-in strobe, the present invention can be applied to an external strobe as long as guide number information of the strobe can be input.

[0045]

As apparent from the above description, the present invention provides
If the main subject is located farther than the effective reach of the strobe light during backlighting, strobe light emission is prohibited,
Useless light emission is eliminated, and the battery life can be extended by suppressing the amount of battery used. Further, in this case, since the exposure is corrected so that the main subject is properly exposed, the proper exposure can be performed on the main subject even when the strobe is not fired in the backlight.

[Brief description of the drawings]

FIG. 1A is a block diagram showing a main part of an electric circuit according to an embodiment in which an automatic exposure control device for a camera according to the present invention is applied to a lens shutter type camera with a built-in strobe, and FIG. It is a figure which shows a photometry area typically.

FIG. 2 is a diagram showing an exposure interlocking range of the camera as a diagram.

FIG. 3 is a flowchart showing main operations of the camera.

FIG. 4 is a flowchart showing an exposure calculation operation of the camera.

FIG. 5 is a flowchart showing a backlight determination operation of the camera.

[Explanation of symbols]

 Reference Signs List 11 CPU 13 Step-up circuit (DC / DC converter) 15 Strobe circuit 17 Shutter drive circuit 19 Film winding motor drive circuit 21 Main photometric element (main subject luminance photometric means) 21c Main photometric circuit 23 Sub photometric element (peripheral subject luminance photometric means) 23c Sub-photometering circuit 25 Distance measuring circuit (ranging means) 27 DX intercept group 29 Red lamp

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03B 15/05 G03B 15/05

Claims (5)

[Claims] 1. A backlight determining means for determining whether or not a main subject is in a backlight state, and an exposure control means for automatically emitting a strobe at the time of exposure and exposing when the backlight detecting means is determined to be in a backlight state. Distance measuring means for measuring the distance to the main subject; calculating means for calculating the effective reach of the strobe based on aperture value information, film sensitivity information and strobe light emission amount information set at the time of exposure; A back-light strobe light emission prohibiting means for prohibiting strobe light emission when the distance to the main subject measured by the distance means is longer than the effective reach calculated by the calculating means. Exposure control device. 2. The automatic exposure control device for a camera according to claim 1, wherein said backlight determination means includes a main subject photometer for measuring the brightness of the main subject, and a peripheral subject for measuring the subject brightness around the main subject. And an automatic exposure control device for a camera that determines a backlight state when a difference between a main subject luminance measured by the main subject photometer and a peripheral subject luminance measured by the peripheral subject photometer is equal to or greater than a predetermined value. 3. The automatic exposure control device for a camera according to claim 1, wherein the calculating means is based on a main subject luminance measured by the main subject photometric means and a peripheral subject luminance measured by the peripheral subject photometric means. An exposure calculation function for calculating an exposure value, wherein the calculation means is configured such that when the backlight strobe light emission prohibition means prohibits strobe light emission,
An automatic exposure control device for a camera that calculates an exposure value based on subject brightness obtained by correcting the main subject brightness by plus. 4. The automatic exposure control device for a camera according to claim 1, wherein when the backlight determining means determines that the subject is backlit, the main subject brightness is corrected by a predetermined value, and the main subject brightness is corrected based on the corrected main subject brightness. A long-distance subject photographing mode in which the strobe light emission prohibiting means at the time of backlighting prohibits strobe light emission at the time of backlighting, and corrects the main subject luminance by a second predetermined value larger than the predetermined value. Automatic exposure control device for a camera that calculates an exposure value based on the corrected main subject luminance. 5. The automatic exposure control device for a camera according to claim 1, wherein said backlight strobe light emission prohibiting means is provided when said main subject luminance or peripheral subject luminance is equal to or less than a predetermined value, regardless of a distance to said subject. An automatic exposure control device for cameras that does not prohibit strobe light emission.