JP4897153B2 - Automatic exposure control device for camera - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an automatic exposure control device for a camera capable of automatically emitting a strobe when backlit.
[0002]
[Prior art and its problems]
2. Description of the Related Art There is known a camera that has a built-in strobe and has a backlit strobe automatic flash mode that automatically emits a strobe when it is exposed. The determination of backlight is usually determined as 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. In this conventional backlight automatic flash mode, when it is determined that the backlight is backlit, the flash is automatically fired regardless of the distance of the subject. For this reason, when the main subject is far away, the main subject is out of the effective flash range and the amount of light from the strobe is insufficient, resulting in useless light emission and underexposure, as well as wasteful battery consumption. It was.
In the case of a lens-shutter camera, the backlit state has high brightness as the photometric value, so the aperture during shooting is narrowed down, and the flash is automatically fired with a small aperture, so the effective distance of the strobe light is further shortened. The possibility of wasted light emission was high.
[0003]
OBJECT OF THE INVENTION
The present invention has been made in view of the problem of the conventional automatic flash emission during backlighting, and provides an automatic exposure device for a camera that reduces unnecessary flash emission during backlighting and enables proper exposure. Objective.
[0004]
  The present invention that achieves this object is based on the strobe, the photometric means for measuring the luminance of the main subject and its surrounding subjects, the distance measuring means for measuring the distance to the main subject, and the photometric results of the photometric means A backlight determining means for determining whether or not the main subject is in a backlight state; a calculating means for calculating an effective reach distance of the strobe light based on the aperture value information, the ISO sensitivity information corresponding to the film sensitivity, and the light emission amount information of the strobe light; , When the distance to the main subject measured by the distance measuring means is equal to or greater than the effective reach distance calculated by the calculating means, a strobe emission prohibiting means during back light that inhibits flash emission, a photometric result of the photometric means, and Strobe light emission exposure control means for calculating an exposure value based on ISO sensitivity information and exposing with the calculated exposure value. When the backlight determining means determines that the backlight, and the backlight when the flash prohibiting means does not prohibit the emission of the strobe when the serial flash emission prohibition mode is not selected,When the luminance difference between the peripheral subject luminance and the main subject luminance is greater than the first predetermined value, the first predetermined value is subtracted from the peripheral subject luminance, and when the luminance difference is equal to or less than the first predetermined value, the peripheral The luminance difference is subtracted from the subject luminance, and the periphery after the subtractionThe exposure value is calculated based on the subject brightness, and the exposure is performed by emitting the strobe according to the calculated exposure value. When the backlight determining means determines that the backlight is back when the light emission is prohibited,When the luminance difference between the peripheral subject luminance and the main subject luminance is larger than the second predetermined value that is larger than the first predetermined value, the second predetermined value is subtracted from the peripheral subject luminance, and the luminance difference is the second luminance value. When the difference is less than the predetermined value, the luminance difference is subtracted from the peripheral subject luminance, and the peripheral after the subtractionThe exposure value is calculated based on the subject brightness, and the exposure is performed without causing the strobe to emit light according to the calculated exposure value.
  The metering means includes a main subject metering means for metering the brightness of the main subject and a peripheral subject metering means for metering the subject brightness around the main subject, and the backlight determination means includes the main subject metering means. If the difference between the main subject brightness and the surrounding subject brightness measured by the surrounding subject metering means is greater than or equal to a predetermined value, it is determined that the backlight is in the backlit state.
  The strobe emission exposure control means has an exposure calculation function for calculating an exposure value based on the main subject brightness measured by the main subject metering means and the peripheral subject brightness measured by the peripheral subject metering means, and the strobe emission exposure control The means calculates the difference between the peripheral subject brightness and the main subject brightness as the first or second predetermined value.The main subject isThe subject brightness is corrected to achieve a positive exposure.
  Camera automatic exposure control device of the present inventionInThe backlight strobe 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 surrounding subject is not more than a predetermined value.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described below with reference to the drawings. FIG. 1A is a block diagram showing an essential part of an electric circuit of an embodiment in which the automatic exposure control device for a camera according to the present invention is applied to a lens shutter type camera with a built-in flash, and FIG. It is a figure which shows typically the photometry area | region.
[0006]
This lens shutter type camera includes a CPU 11 having a control function for comprehensively controlling the operation of the entire camera, a calculation function for calculating an exposure value, a distance to a subject, and the like. The CPU 11 operates in a state where the voltage of the battery BATT is boosted by a booster circuit (DC / DC converter) 13 and supplied as a constant voltage. The CPU 11 is connected with a built-in strobe flash circuit 15, a shutter drive circuit 17 for driving the shutter, and a film winding motor drive circuit 19 for winding the film. The strobe circuit 15 is a circuit for emitting a built-in strobe equipped with a Fresnel lens, a xenon tube, a reflector, and the like as a light emitting unit. The strobe circuit 15 stores a main capacitor for accumulating charges, a charging circuit for charging the main capacitor, and discharging the main capacitor. And a light emission control circuit for causing the xenon tube to emit light and stopping the light emission. The strobe circuit 15 operates in response to a control signal from the CPU 11.
[0007]
This camera, as photometric means, converts the current output of the main photometric element 21 and the sub photometric element 23 that measure the luminance of the main subject into voltage and outputs it as a main subject luminance signal to the CPU 11, and the main photometric circuit 21c of the main subject. A sub-photometry element 23 that measures the ambient luminance and a sub-photometry circuit 23c that converts the current output of the sub-photometry element 23 into a voltage and outputs it as a peripheral subject luminance signal to the CPU 11 are provided. FIG. 1A shows the relationship between the photometry area of the main photometry element 21 and the sub photometry element 23 with respect to the shooting screen. In the illustrated embodiment, one main photometering element 21 and one sub photometering element 23 are used, but a configuration including a plurality of subphotometering elements 23 may be used.
The CPU 11, the main photometric element 21, the main photometric circuit 21c, the sub photometric element 23, and the sub photometric circuit 23c constitute a backlight determining unit. That is, the CPU 11 obtains the average subject brightness based on the main subject brightness signal and the peripheral subject brightness signal from the photometry circuits 21c and 23c, and further determines whether the light is backlit from the difference between the main subject brightness signal and the peripheral subject brightness signal. For example, the CPU 11 determines that the surrounding subject brightness is higher than the main subject brightness by a predetermined value or more as backlight.
[0008]
The camera further includes a distance measuring circuit 25 as distance measuring means. The distance measuring circuit 25 includes distance measuring means using a so-called triangulation method, and outputs a distance measurement signal from the distance measuring means to the CPU 11. If the distance measuring means is a so-called active system, it includes a light emitting element and a light receiving element, the distance measuring light emitted by the light emitting element and reflected by the main subject is received by the light receiving element, and the position signal corresponding to the light receiving position is received by the light receiving element. The thing of the structure output to CPU11 can be used. The CPU 11 calculates a baseline distance based on the input position signal, and further calculates a distance from the baseline distance to the main subject. In the case of the so-called phase difference type passive method, a pair of subject images obtained by dividing the main subject light into pupils are received by the line sensors, photoelectrically converted, and luminance distribution signals of the pair of main subject images are 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.
Note that the distance measuring circuit 25 can measure a subject area included in a main subject within the light metering area of the main light metering element 21 regardless of which method is used. Further, the distance to the subject may be either the subject distance or the shooting distance, and may be any distance from an arbitrary base point of the camera.
[0009]
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 interlocked with the main switch button. When the main switch is OFF, the CPU 11 turns off the power to the strobe circuit 15 and other peripheral circuits to enter a sleep state. The camera can be turned on by turning on the power to the camera. The metering switch SWS and the release switch SWR are interlocked with the shutter button, and the metering switch SWS is turned on when the shutter button is half-pressed, and the metering switch SWS is kept on when the shutter button is fully pressed. The release switch SWR is turned on. The CPU 11 executes photometry and distance measurement processing when the photometry switch SWS is turned on, and executes exposure processing when the release switch SWR is turned on.
[0010]
The lens shutter type camera further includes a DX section group 27 for reading the ISO sensitivity by a combination of DX sections that come into contact with the DX code formed on the surface of the loaded film cartridge, and whether the back cover is opened or closed. A back cover switch SWBACK for detection, an automatic exposure mode setting switch SWAEMODE for setting an automatic exposure mode, and an automatic focus mode setting switch SWAFMODE for setting an automatic focus mode are provided. The CPU 11 detects the on / off state of these switches and performs the following processing and setting. The ISO sensitivity is identified from the combination of signal levels of the DX segment group 27, and the ISO sensitivity is set. Each time the automatic exposure mode setting switch SWAEMODE is turned on, the exposure mode is changed to the flash automatic flash mode, red-eye prevention automatic flash mode, flash flash prohibit mode, backlight automatic flash mode, shutter long shutter speed interlock 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 far-field shooting mode (strobe light emission prohibition) are alternately selected and set.
[0011]
Further, this 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 eyepiece frame side on the back of the camera body.
Although this lens shutter type camera has the functions of a normal camera, illustration and description thereof are omitted because it is not necessary for understanding the present invention.
[0012]
In the embodiment of the present invention, in the distant view shooting mode, the flash is prohibited from being emitted, and when the main subject is backlit, the main subject luminance is limited to the first predetermined value to correct the luminance difference. The first predetermined value is equivalent to 1 Ev in this embodiment.
The backlit flash automatic flash mode is a mode that automatically fires the flash when the main subject is determined to be backlit.In this embodiment, when the main subject is located farther than the effective flash range, In addition to prohibiting light emission, the main subject luminance is corrected to a luminance difference with the second predetermined value as a limit. This second predetermined value is larger (brighter) than the first predetermined value, and is equivalent to 2 Ev in this embodiment.
Also, in this embodiment, in the backlit strobe mode, strobe lighting is prohibited when the surrounding subject brightness is lower than the predetermined brightness even if the backlight is back and the main subject is located farther than the strobe effective distance. do not do.
[0013]
The exposure interlocking range of this camera is shown as a diagram in FIG. In the diagram, the numbers on the left of the vertical axis represent the aperture values Av and F number in the apex display, and the horizontal axis represents the shutter speed (seconds). The right downward line represents the exposure value Ev in the apex display, and the coordinates on the right downward line indicate a combination of the aperture value Av and the shutter speed Tv that become the exposure value Ev. If the exposure value determined by the aperture and shutter speed is Evs,
Evs = Av + Tv = log₂(Fno x T)²
It becomes.
[0014]
The number on the right vertical axis in FIG. 2 is the effective reach distance (m) of the built-in strobe light at the aperture value Av, that is, the distance of the subject that can be effectively stroboscopically irradiated. The built-in strobe of this embodiment has an ISO 100 guide number Gno of 11 and an apex display value Gv of 7. Hereinafter, a case where the film sensitivity is ISO 100 will be described.
The strobe reach distance (m) is a value determined by the strobe guide number Gno and the F number Fno corresponding to the aperture value Av set based on the set exposure value Ev.
Gno / Fno
It is obtained by.
[0015]
The lens shutter of this camera has an aperture interlocking range of 5 to 9 for the aperture value Av in apex display and F5.6 to F22 for the F number. The shutter speed interlocking range is 1/0 on the low speed side for convenience of illustration. 16 seconds, 1/300 seconds on the high speed side, and 4 to 8 + 1/4 at the apex display shutter speed Tv. A solid line FM1 is a program line of this camera. The interlocking range (FM interlocking range) by the flashmatic method is an area above and above the program line FM1.
[0016]
In FIG. 2, a broken line FM2 indicates the limit of the effective reach distance of the strobe light, and an area below the broken line FM2 indicates a strobe light emission prohibition area that prohibits strobe light emission because the subject is too far away. . In the present embodiment, the strobe reach distance boundary FM2 is a case where the subject distance measured is 1 Ev farther than the strobe effective reach limit distance determined by the aperture value set according to the subject brightness.
[0017]
In the present embodiment, the strobe light emission prohibition region is characterized in that exposure correction larger than the far-field shooting exposure correction is performed in order to compensate for a reduction in exposure amount due to strobe light emission prohibition.
[0018]
In the normal automatic light emission mode of this camera, that is, the automatic light emission mode at low luminance, the flash is automatically emitted by the flashmatic method to prevent camera shake when the shutter speed becomes slower than a predetermined value. 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 emitted when the shutter speed becomes slower than this. .
[0019]
Next, the main operation of this camera will be described with reference to the flowcharts shown in FIGS. FIG. 3 shows the main processing of this camera. This process is executed with the battery BATT loaded.
[0020]
"Main processing"
"Power switch off"
When the main process is entered, it is checked whether the power switch is on or off (S101). If it is off, the red lamp 29 is turned off, the charging operation is stopped in the strobe circuit 15, the power supply to other peripheral devices is cut off, and the low power consumption mode is entered (S101; OFF, S103, S105). , S107). In this low power consumption mode, the CPU 11 itself is in an operable state by a low-speed clock, and the process of periodically starting and checking the power switch state is repeated.
[0021]
"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 turned off (S109). If both are turned off, the strobe circuit 15 is started to charge the strobe and the power to other peripheral circuits is also turned on (S109; OFF, S111). Then, it is checked whether or not the strobe circuit 15 is fully charged (S113). If it is not fully charged, the process returns to S101 (S113; N, S101). 15 is stopped and the process returns to S101 (S113; Y, S115, S117, S101). That is, as long as the power switch is ON, strobe charging is continued and a fully charged state is maintained.
[0022]
“Metering switch SWS ON”
When the metering switch SWS is turned on (S109; SWS ON), the flash charging process is stopped (S119), the metering is performed to input the main subject luminance and the peripheral subject luminance signal (S121), and the distance measurement is performed to calculate the subject distance. (S123). Further, the backlight is determined (S129), and the exposure calculation is performed (S131).
[0023]
“When firing the flash”
Next, it is determined whether or not the strobe light is emitted by determining whether or not “1” is set in the strobe light emission flag (S133). The strobe flash flag is set to “1” because, in addition to the forced flash mode, the exposure value Ev is set to the flash switching reference Ev value in the automatic flash mode when it is determined that the backlight is backlit. This is the case, for example.
[0024]
When the strobe is caused to emit light (S133; Y), the red lamp 29 is blinked at the first cycle (4 Hz) (S135), and it is checked whether the full charge is started after starting the strobe charge (S137, S139). Since the red lamp 29 blinks in the first cycle, the photographer can recognize that charging is in progress. If it is not full charge, it is checked whether or not the photometric switch SWS is ON (S139; N, S141). If the photometric switch SWS is ON, the process returns to S137 and the strobe charging is continued (S141; ON, S137). ).
[0025]
When the battery is fully charged (S139; Y), the red lamp 29 is turned on (continuous lighting) to indicate that the strobe charging is completed, the strobe charging is stopped, and the process proceeds to S149 (S143, S145, S149). Then, the state of the photometry switch SWS and the release switch SWR is checked (S149).
If the metering switch SWS is turned off in the check of S141, the process returns to S101 (S141; OFF, S101). If the power switch SWMAIN is turned on thereafter, the red lamp 29 is blinked by the processing of S101 to S113. If the strobe is fully charged in a continuous state and is fully charged, the red lamp 29 is turned off and the strobe charging is terminated (S113; Y, S115, S117).
[0026]
While the photometric switch SWS is ON, the CPU waits for the release switch SWR to be ON (S149; SWS ON & SWR OFF). When the photometric switch SWS is turned off, the red lamp 29 is turned off and the process returns to S101 (S149; SWS OFF, S151, S101). When the red lamp 29 is turned off, the photographer knows that the strobe does not emit light.
[0027]
"Exposure processing"
When the release switch SWR is turned on, the red lamp 29 is turned off (S149; SWR & SWS ON, S153). Then, it is checked whether or not strobe light is emitted (S155), and if strobe light is emitted, the strobe light is emitted according to the exposure value obtained by emitting the strobe light (S155; Y, S157), and the film is wound up (S161). ), The process returns to S101.
[0028]
When the strobe is not emitted (S133; N), the red lamp 29 is turned off, and the state of the photometry switch SWS and the release switch SWR is checked (S147, S149). When the release switch SWR is turned on (S149; SWS & SWR ON), the red lamp 29 is turned off, the exposure operation is performed without emitting the strobe at the exposure value when the strobe is not emitted, the film is wound up, and the process returns to S101 ( S153, S155; N, S159, S161, S101).
[0029]
"Backlight judgment processing"
Next, the backlight determination process executed in S129 will be further described in detail with reference to the flowchart shown in FIG.
In the backlight determination process, first, a luminance difference ΔBv between the main subject luminance Bv_main and the peripheral subject luminance Bv_sub is obtained (S201). Then, it is checked whether or not the luminance difference ΔBv is equal to or greater than a predetermined value of 1 Ev (S203). That is, in this embodiment, when the luminance difference ΔBv is 1 Ev or more, it is determined to be backlight, and when it is not 1 Ev or more, it is not determined to be backlight.
When the brightness difference ΔBv is 1 Ev or more (when the peripheral subject brightness Bv_sub is higher than 1 Ev (bright)), the strobe emission flag is set to “1” and the process proceeds to S211 (S203; Y, S205, S211) ), When the brightness difference ΔBv is not 1 Ev or more, the brightness difference ΔBv is rewritten to 0, the flash emission flag is set to “0”, and the process proceeds to S211 (S203; N, S207, S209, S211).
That is, when it is determined that the light is backlit, “1” is set in the strobe light emission flag, and strobe light emission is enabled during exposure.
[0030]
In S211, it is checked whether or not the distance measurement value of the main subject is greater than or equal to the strobe reach distance. The strobe reach distance (m) is a value determined by the strobe guide number Gno corresponding to the ISO sensitivity and the F number Fno corresponding to the aperture value Av set based on the set exposure value Ev.
Gno / Fno
It is demanded by.
[0031]
“When the backlight is back and the distance measurement value is not more than the flash range”
If the measured distance of the main subject is not equal to or greater than the flash reach distance (S211; N), it is not in the distant shooting mode (S213; N), on the condition that the back cover is not opened and there is no film (S215). N), 1Bv is set as a predetermined value to the limit correction value ΔBvlimit for exposure correction (S217).
Then, it is compared whether or not the luminance difference ΔBv is larger than the limit correction value ΔBvlimit (S223). If the brightness difference ΔBv is not larger (S225, S227), the process proceeds to S227 as it is (S223; N, S227).
[0032]
In S227, a value obtained by subtracting the luminance difference ΔBv from the peripheral subject luminance Bv_sub is set as the subject luminance Bv. Then, whether or not the subject brightness Bv is less than the minimum brightness Bvmin is compared, and if it is not less, the process returns as it is (S229; N), and if it is less than that, the subject brightness Bv is rewritten with the value of the minimum brightness Bvmin. Return (S229; Y, S231).
With the above processing, when the backlight and the subject distance are less than the strobe reach distance, the luminance obtained by subtracting the luminance difference Bv (maximum 1 Ev) from the peripheral subject luminance Bv_sub is set as the subject luminance Bv, and the strobe is emitted.
[0033]
“When the backlight is back and the distance measurement is greater than the flash reach”
If the distance measurement value is greater than or equal to the flash range, the proper exposure value will not be obtained even if the flash is fired. Therefore, if the distance measurement value is greater than or equal to the flash reach distance, the flash emission flag is set to “0” to prohibit the flash emission (S211; Y, S219). Then, 2Ev, which is a second predetermined value, is set to the limit correction value ΔBvlimit, and the process proceeds to S223 (S221, S223). That is, when the subject is located farther than the flash reach distance, the limit correction value ΔBvlimit is set to a value twice the normal first predetermined value. If the back cover is open or there is no film (S215; Y), the flash emission flag is set to “0” (S219), the limit correction value ΔBvlimit is set to 2Bv, and the process proceeds to S223 (S221). , S223).
[0034]
Then, it is compared whether or not the luminance difference ΔBv is larger than the limit correction value ΔBvlimit (S223). If the brightness difference ΔBv is not larger (S225, S227), the process proceeds to S227 as it is (S223; N, S227).
[0035]
In S227, a value obtained by subtracting the luminance difference ΔBv from the peripheral subject luminance Bv_sub is set as the subject luminance Bv. Then, whether or not the subject brightness Bv is less than the minimum brightness Bvmin is compared, and if it is not less, the process returns as it is (S229; N), and if it is less than the subject brightness Bv, the subject brightness Bv is rewritten and set with the value of the minimum brightness Bvmin. Return (S229; Y, S231).
As a result of the above processing, when the backlight and subject distance are equal to or longer than the strobe reach distance, the strobe is not fired, and the brightness is obtained by subtracting the brightness difference Bv (maximum 2 Ev) from the surrounding subject brightness Bv_sub, that is, positive exposure. The obtained luminance is set as the subject luminance Bv.
[0036]
In this embodiment, the back cover is not closed when the far-field shooting mode is set (S213; Y) regardless of whether there is no backlight or the distance measurement value is less than the flash reach distance. If no film is loaded (S215; Y), the flash emission flag is set to “0” in S219, so that the flash is not emitted. In this case, 2Bv is set as the limit correction value ΔBvlimit (S221).
[0037]
"Exposure calculation processing"
Next, the exposure calculation process executed in S131 will be described in detail with reference to FIG. When the calculation process is started, first, the DX code input via the DX segment group 27 is converted into the apex display film sensitivity Sv (S301), and the appropriate exposure value Ev is obtained from the film sensitivity Sv and the measured subject brightness Bv. (S303). Next, it is checked whether or not the photographing mode is strobe light emission auto (S305).
[0038]
“Flash Auto”
In the flash emission auto shooting mode, for example, the flash automatic flash mode or the backlight automatic flash mode, if the shooting mode is auto, it is checked whether the exposure value Ev is equal to or less than the emission switching value Ev_f1 (S305; Y, S307).
The light emission switching reference value Ev_f1 is a light emission switching reference value Ev which is a boundary value indicating whether the strobe emits light or not, and is 10.5 in this embodiment as shown in FIG.
If it is less than the emission switching reference value Ev_f1, “1” is set to the strobe emission flag that causes the strobe to emit light, and the process proceeds to S311 (S307; Y, S309, S311). Skip to S309 (S307; N, S311).
[0039]
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 a lower limit exposure value Ev in the strobe automatic light emission mode and the strobe forced light emission mode. In this embodiment, the shutter speed Tv at the minimum exposure value Ev_min_a in ISO 100 is 1/16 second.
If the set exposure value Ev is less than or equal to the minimum exposure value Ev_min_a, the set exposure value Ev is rewritten with the value of the minimum exposure value Ev_min_a, and the process proceeds to S323 (S311; Y, S313, S323). S311; N, S323).
[0040]
In S323, it is checked whether or not the set exposure value Ev is greater than or equal to 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 (S323; Y, S325), and if not, the process returns as it is (S323; N). The processes in S323 and S325 are processes that limit the upper limit value of the exposure value Ev.
[0041]
“In the forced flash mode”
If the flash emission auto is not set, it is checked whether or not the shooting mode is the forced emission mode (S305; N, S315). In the case of the forced light emission mode, the process proceeds to S309 (S315; Y), and proceeds to S323 through the processes of S309 to S313.
[0042]
“When neither strobe auto nor forced flash”
If it is not the strobe auto or forced flash mode (S305; N, S315; N), “0” is set to the strobe flash flag (S317), and whether or not the set exposure value Ev is less than or equal to the lower limit exposure value Ev_mins in the flash prohibit mode. A check is made (S319). The lower limit exposure value Ev_mins is an exposure value Ev determined by the open aperture value of the camera and the longest shutter time. In this embodiment, the shutter speed Tv at the lower limit exposure value Ev_mins in ISO 100 is 2 seconds. If the set exposure value Ev is less than or equal to 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 (S319; Y, S321, S323). , S323). The processes of S319 and S321 are a lower limit value limiting process for the set exposure value Ev.
When the process proceeds to S323, the process returns through the upper limit limiting process of S323 and S325.
Note that when the flash mode is not the strobe auto mode or the forced flash mode, the flash mode is prohibited.
[0043]
According to the embodiments of the present invention described above, in the flash automatic flash mode, the flash emission is prohibited when the main subject distance is longer than the strobe light effective distance when the backlight is determined to be backlit. Light emission is lost and battery consumption can be prevented. Further, when the flash emission is prohibited, exposure correction is performed in accordance with the luminance of the main subject, so that the main subject can be properly exposed. Furthermore, in the embodiment of the present invention, if the subject brightness is lower than a predetermined value even if it is determined that the backlight is back, the flash is not prohibited regardless of the distance of the subject. Is no longer misunderstood.
[0044]
As described above, the present invention has been described based on the embodiment applied to the lens shutter type camera with a built-in strobe. However, the present invention can be applied to an external strobe as long as the guide number information of the strobe can be input.
[0045]
【The invention's effect】
As is apparent from the above description, the present invention prohibits flash emission when the main subject is located farther than the effective range of the flash light during backlighting, so that unnecessary light emission is eliminated and battery usage is reduced. Battery life can be extended. Further, in this case, since exposure correction is performed so that the main subject has an appropriate exposure, the main subject can be properly exposed even when the strobe is not illuminated during backlighting.
[Brief description of the drawings]
FIG. 1A is a block diagram showing the main part of an electric circuit of an embodiment in which the 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 diagram showing a main operation of the camera in a flowchart.
FIG. 4 is a flowchart showing an exposure calculation operation of the camera.
FIG. 5 is a flowchart illustrating a backlight determination operation of the camera.
[Explanation of symbols]
11 CPU(Calculation means, back light determination means, strobe emission prohibition means during back light, strobe light exposure control means)
13 Booster circuit (DC / DC converter)
15 Strobe circuit(strobe)
17 Shutter drive circuit
19 Film winding motor drive circuit
21 Main metering element (Photometric means,Main subject brightness metering)
21c Main metering circuit
23 Sub metering element (Photometric means,Peripheral subject luminance metering means)
23c Sub metering circuit
25 Ranging circuit (ranging means)
27 DX sections
29 Red lamp

Claims (4)

Strobe,
A photometric means for measuring the luminance of the main subject and the surrounding subjects;
Ranging means for measuring the distance to the main subject;
Back light determination means for determining whether or not the main subject is in a back light state based on the light measurement result of the light measurement means;
A calculation means for calculating an effective reach distance of the strobe light based on the aperture value information, the ISO sensitivity information corresponding to the film sensitivity, and the flash emission amount information;
A strobe light emission exposure control means having a selectable strobe light emission prohibiting mode;
A backlit strobe emission prohibiting means for prohibiting strobe light emission when the distance to the main subject measured by the distance measuring means is equal to or greater than the effective reach calculated by the calculating means,
The strobe light emission exposure control means includes:
When the flash emission prohibiting mode is not selected, the backlight determining means determines that the backlight is backlit, and when the backlight strobe emission prohibiting means does not prohibit the flash emission, the surrounding subject brightness and the main subject brightness When the luminance difference is larger than the first predetermined value, the first predetermined value is subtracted from the peripheral subject luminance, and when the luminance difference is equal to or smaller than the first predetermined value, the luminance difference is subtracted from the peripheral subject luminance. And calculating an exposure value based on the luminance of the surrounding subject after the subtraction , and exposing the flash with the calculated exposure value, and when the flash emission prohibiting mode is selected or when the backlight is backlit When the flash emission prohibiting means prohibits the flash emission, when the backlight determination means determines that the backlight is backlit, the brightness difference between the surrounding subject brightness and the main subject brightness is The second predetermined value is subtracted from the peripheral subject brightness when the second predetermined value is greater than the first predetermined value, and the peripheral subject brightness is subtracted when the brightness difference is less than or equal to the second predetermined value. An automatic exposure control device for a camera, wherein the brightness difference is subtracted from the image, an exposure value is calculated based on the brightness of the surrounding subject after the subtraction , and the exposure is performed without causing the strobe to emit light based on the calculated exposure value. . The automatic exposure control device for a camera according to claim 1, wherein the photometry means includes main subject photometry means for measuring the brightness of a main subject, and peripheral subject photometry means for measuring subject brightness around the main subject. The backlight determining unit determines whether the backlight is in a backlight state when the difference between the main subject luminance measured by the main subject metering unit and the peripheral subject luminance measured by the peripheral subject metering unit is equal to or greater than a predetermined value. apparatus. 3. The automatic exposure control device for a camera according to claim 2, wherein the strobe emission exposure control means calculates an exposure value based on the main subject brightness measured by the main subject metering means and the peripheral subject brightness measured by the peripheral subject metering means. The strobe light emission control means is configured to subject the difference between the peripheral subject luminance and the main subject luminance to a positive exposure with a difference between the first and second predetermined values or less. An automatic exposure control device for cameras that corrects brightness. 4. The automatic exposure control device for a camera according to claim 1, wherein the strobe emission prohibiting unit at the time of backlighting is set to a distance to the subject when the main subject luminance or the peripheral subject luminance is a predetermined value or less. 5. Regardless of the camera's automatic exposure control, it does not prohibit the use of flash.

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