JPH055087B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an automatic flash control method and device for performing daytime synchronized photography, and more specifically, to an automatic flash control method and device for performing daytime synchronized photography, and more specifically, a system that changes the flash control level of an autostrobe by determining whether the scene is frontlit or backlit. The present invention relates to a method and apparatus.

Daytime synchronized photography is a photography method that combines a camera that automatically controls exposure according to the brightness of the subject and a strobe, and is mainly used for photographing scenes where the main subject is backlit. In this backlit scene, the main subject is illuminated with strobe light, avoiding underexposure, and the exposure is appropriate in the background where strobe light does not work, making it possible to take pictures that cover the entire frame. become.

However, in conventional daytime sync photography, the amount of flash light that contributes to film exposure is controlled so that it remains constant regardless of the lighting conditions of the scene, making it difficult to properly expose the main subject. It was hot. For example, when using a strobe that fires at full power, such as when shooting with a strobe at night, the main subject is often overexposed.Also, when using a strobe that controls the flash so that the strobe light is 20% to 30% of the appropriate exposure amount, Often underexposed.

Based on the above background, it is an object of the present invention to provide an automatic light control method and device that controls the amount of light emitted according to the lighting condition of a scene. The present invention measures the lighting condition of the scene, determines whether it is frontlit or backlit, and in the case of backlighting, changes the dimming level depending on the degree of backlighting. Therefore, when there is strong backlight, the amount of light emitted by the strobe is large,
In weak backlight, the strobe light output is low, so you can get the main subject almost the correct exposure in any scene.

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

In Fig. 1, the light receiving element 1 measures the brightness of the central part (which may include a part of the peripheral part) where the main subject is likely to be present, and the light receiving element 2 measures the brightness of the peripheral part (also the central part). ). Adjustment of this measurement area can be easily achieved by using an optical system.
Further, since average photometry and partial photometry have already been implemented in the field of cameras, specific disclosure thereof will be omitted. The light receiving elements 1 and 2 are connected to operational amplifiers 3 and 4, and generate a photocurrent according to the intensity of the incident light. This photocurrent is logarithmically compressed by log diodes 5, 6 connected to the feedback circuits of operational amplifiers 3, 4.

The output voltages of the operational amplifiers 3 and 4 are input to a differential amplifier 7 and converted into a signal corresponding to the brightness difference between the center and peripheral parts of the scene. This signal indicates whether the scene is frontlit or backlit, and to what extent. Therefore, if this signal is used as a light control level, the light control level can be changed depending on the lighting condition of the scene, and the main subject can be properly exposed. However, if you do this, the strobe will not emit light in front-lit scenes, and in extreme backlighting, the strobe's maximum light output will be exceeded. Especially in a bright room, even in a brightly lit scene.
Since the color temperature changes when shooting in the morning and evening, color reproduction will be better if you mix the strobe light when shooting. Therefore, in front-lit scenes, the strobe light is adjusted so that it mixes with natural light by a certain percentage, for example, 30%. In this case, change the exposure value EV to make the natural light insufficient by the amount of strobe light.
In extreme backlight situations, the light is adjusted in the same way as for normal night photography. Such dimming can be achieved by providing a limiter that determines the maximum and minimum values of the output signal of the differential amplifier 7.

A resistor 9 and a Zener diode 10 are connected in series, and a diode 11 is connected to a connection point between these to form a minimum value setting circuit. Also resistance 1
2, Zener diode 13, and diode 1
4 constitutes a maximum value setting circuit. Between the minimum value and the maximum value, the output signal of the differential amplifier 7 is input to the buffer circuit 16 through the diode 15. This buffer circuit 16 outputs a signal having the same waveform as shown in FIG. 5 as a dimming level signal.

The analog switch 17 is connected to the buffer circuit 1.
6 and the constant voltage determined by resistors 18 and 19 are taken out and applied to comparator 2.
Input to one side input terminal of 0. This analog switch 17 is switched according to the output signal of the comparator 21, and the output signal of the buffer circuit 16 is taken out during daytime synchronized photography, and the voltage at the connection point between resistors 18 and 19 is taken out during nighttime flash photography. taken out. In order to determine whether it is daytime synchronized photography or strobe photography, a light receiving element 22, an operational amplifier 23, and a log diode 24 are provided to measure the average light of the scene. Note that if a circuit for adding the output signals of the operational amplifiers 3 and 4 is provided, the light receiving element 22 and the like are not necessary. The output signal of the operational amplifier 23 is compared with a reference voltage determined by resistors 25 and 26 in the comparator 21 . This reference voltage is set to a value corresponding to the subject brightness at which the shutter speed reaches the limit of camera shake and the use of a strobe is required.

Phototransistor 2 for measuring strobe reflected light
8 and a capacitor 29 are connected in series,
When the switch 31 is turned off at the same time as the flash discharge tube 30 emits light, the capacitor 29 is charged with a photocurrent corresponding to the strobe reflected light. This capacitor 29
The terminal voltage is input to the + side input terminal of the comparator 20, and when this terminal voltage reaches the voltage (dimmer level) output from the analog switch 17, the output signal of the comparator 20 becomes "H".
This is sent to the light emission control circuit 32 as a light emission stop signal.

The light emission control circuit supplies electrical energy stored in the main capacitor to the flash discharge tube 30 and converts it into light when the synchro switch 33 is synchronized with the shutter of the camera. When the integral value of the strobe reflected light reaches the dimming level while the flash discharge tube 30 is emitting light, the energization of the flash discharge tube 30 is stopped.

FIG. 2 shows the photometric areas of the light receiving elements 1 and 2. Light-receiving element 1 photometers area A of scene 35, and light-receiving element 2 measures area B. Since A≧B in a frontlit scene and A<B in a backlit scene, the type of scene can be determined from the difference in the outputs of the light receiving elements 1 and 2.

FIG. 3 shows another embodiment of the division of the photometric area.

In the embodiment of FIG. 4, region B encompasses region A.

FIG. 5 shows the amount of strobe light emitted during daytime synchronized photography. The brightness difference is obtained by subtracting the brightness of area A from the brightness of area B, and is expressed using brightness values (BV) as a scale. Brightness difference is zero
When the BV is below, the scene is frontlit and the strobe light output is 30% of the standard value. This means that the strobe light that contributes to film exposure is 30% of the appropriate exposure amount. When the brightness difference is between 0 and 3BV, the scene is weakly backlit, and the amount of strobe light emitted changes depending on the degree of backlighting. This change is
In addition to the linear change as in this embodiment, the change may be curved or stepwise. Brightness difference is 3BV
In the above cases, there is strong backlighting, and at this time, the strobe light output is 100%, and the strobe fires just like when shooting with a flash at night.

In the present invention having the above configuration, in daytime synchronized photography, the strobe light control level changes depending on the lighting condition of the scene, so even if the main subject, which is likely to be in the center, is backlit. can be exposed to almost the appropriate level.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. FIGS. 2 to 4 are explanatory diagrams showing examples of division of photometric areas. FIG. 5 is a graph showing the relationship between the brightness difference and the strobe light emission amount during daytime synchronized photography. 1...A light-receiving element that measures the center of the scene, 2...
. . . A light receiving element that measures the peripheral area of the scene, 3 . . . A light receiving element that measures the average light of the scene, 7 . . . Differential amplifier, 2
0, 21... Comparator, 28... Phototransistor for measuring strobe reflected light, 30... Flash discharge tube, 31... Synchro switch.

Claims (1)

[Claims] 1. An automatic light control method that measures the brightness between the center and peripheral parts of a scene and changes the light control level according to the brightness difference during daytime synchronized photography, comprising: It is classified into forward light area, weak backlight area, and strong backlight area according to the value, and in the front light area, the strobe light emission amount is kept at the first dimming level that is less than the reference value, and in the strong backlight area, the strobe light emission amount is kept at the first dimming level. An automatic light control method characterized in that the light control level is maintained at a second light control level serving as a reference value, and the light control level is changed in accordance with a luminance difference in weakly backlit areas. 2 When flash photography is performed in either frontlight mode or backlight mode, the brightness at the center of the scene is adjusted using an automatic light control device that stops flash discharge tube light emission when the integral value of the flash reflected light reaches the light control level. means for detecting the brightness around the scene; means for inputting the output signals of these detection means and outputting the brightness difference; A means for determining a backlit scene, when the scene is determined to be a frontlit scene, the strobe light emission amount is set to a first light control level lower than a reference value, and when it is determined to be a weakly backlit scene among the backlit scenes, the The light control level is changed between the first light control level and a second light control level that is approximately equal to the reference value, and the second light control level is set when a strong backlight scene is determined. An automatic light control device comprising: control means for setting a light control level.