JPS5984229A - Method and device for automatic dimming - Google Patents

Abstract

PURPOSE:To obtain proper exposure even when an object is on rear-light condition by measuring luminance at the center part and circumferential part of a scene and varying a dimming level in daylight synchronized photography according to their luminance difference. CONSTITUTION:Luminance signals corresponding to the center and circumferential part of a scene measured by photodetecting elements 1 and 2 are inputted to a differential amplifier 7 through operational amplifiers 3 and 4. Its difference output is inputted to a switch 17 through the diode 15 of a minimum value setting circuit and a buffer circuit 16. The averaged photometric value of a photodetecting element 22 is compared with a constant voltage determined by resistances 25 and 26 by a comparator 21, which outputs a signal for selecting a switch 17; a dimming level signal is led out of the circuit 16 in daylight synchronized photography as a substitute for a constant voltage determined by resistances 18 and 19 and compared with the output of the flash discharge tube 30 of a PT 28 by a comparator 20. When they become equal to each other, a emission control circuit 32 stops powering on the discharge tube 30 to obtain proper exposure.

Description

[Detailed Description of the Invention] The present invention relates to an automatic flash control method and device for daytime synchronized photography, and more specifically, to determine whether the scene is frontlit or backlit and change the flash control level of an auto strobe. The present invention relates to a method and apparatus for doing so.

Synchronized photography is a combination of a camera and strobe that automatically controls exposure according to the brightness of the subject, and is mainly used for shooting scenes where the main subject is backlit. It will be done. In this backlit scene, the main subject is illuminated by the strobe light, which avoids underexposure, and because the background is not illuminated by the strobe light, no light is appropriate, so it is possible to take a clear photo of the entire frame. It becomes possible.

However, in conventional daytime sync shooting, 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, so it is difficult to properly expose the main subject. It was difficult. 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 between 20% and 309° of the appropriate exposure amount, the exposure It is often under.

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 depending on the lighting condition of the scene.

The present invention measures the illumination state of the scene, determines whether the scene is frontlit or backlit, and in the case of backlighting, changes the dimming level depending on the degree of backlighting. Therefore, the main subject can be almost properly exposed in any scene, even though the strobe emits a large amount of light in strong backlight, and the strobe light emits less in weak backlight.

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 there is a high probability that the main subject is present, and the light receiving element 2 measures the brightness of the peripheral part (also the central part). Measure the brightness of Adjustment of this measurement area can be easily realized using an optical system, and has already been implemented as average photometry and single partial photometry in the field of single-lens cameras, so the specific disclosure is Omit this. The light receiving element 1. 21-1
: It is connected to the operational amplifier 8.4 and generates 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 8, 4.

The output voltages of the operational amplifiers 8 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 is a signal that indicates whether the scene is frontlit or backlit, and to what extent. Therefore, if this signal is used as the total light control level, the light control level can be varied depending on the lighting condition of the scene, making it possible to properly expose the main subject. However, this will prevent the strobe from emitting light in front-lit scenes, and will exceed the strobe's maximum light output in extreme backlight situations. Especially in bright interiors, even in daylight situations.

Since the color temperature changes when shooting in the morning and evening, color reproduction will be better if you mix strobe light when shooting. Therefore, in a brightly lit scene, the strobe light is dimmed so as to be mixed with natural light by a certain amount, for example, 805A). In this case, the exposure value EV is changed to make the amount of 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 IO are connected in series,
A diode 1] is connected to these connection points to form a maximum value setting circuit. Further, the resistor 124, the Zener diode 1B, and the diode 14 constitute 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 1
6, a signal having the same waveform as that shown in FIG. 5 is output as a dimming level signal.

The analog switch 17 takes out either the output voltage of the buffer circuit 16 or a constant voltage determined by the resistors 18 and 19, and inputs it to the − input terminals of the comparator 2°. This analog switch 17 is connected to the comparator 2
During daytime synchro photography, the output signal of buffer circuit 16 is taken out, and during nighttime strobe photography, the voltage at the connection point between resistors 18 and 19 is taken out. The light receiving element 22 measures the average light of the scene in order to determine the daytime synchronization shooting ability and strobe photography. Operational amplifier 23. Note that if a circuit for adding the output signals of operational amplifiers 3 and 4 is provided, the light-receiving element 22 and the like are not required.
At , it is compared with a reference voltage added by resistors 25 and 26. This reference voltage is set to a value corresponding to the brightness of the subject where the shutter speed reaches its manual limit and the use of a strobe is required.

The phototransistor 28 and capacitor 29 that measure all of the strobe reflected light are connected in series, and the flash is emitted! 11
When the switch 81 is turned off at the same time as the tube 80 emits light, the capacitor 29 is charged with a photocurrent corresponding to the strobe reflected light. The terminal voltage of this capacitor 29 is input to the + side input terminal of the comparator 20, and when this terminal voltage reaches a voltage (dimmer level) that is lower than the output from the analog switch 17, the output signal of the comparator 20 becomes 111.
”, and this is sent to the light emission control circuit 82 as a light emission stop signal.
sent to.

The light emission control circuit supplies electrical energy stored in the main capacitor to the flash discharge tube 80 and converts it into light when the synchro switch 33 is turned on in synchronization with the shutter of the camera. When the integral value of the strobe reflected light reaches the dimming level while the flash discharge tube 800 is emitting light, the flash discharge tube 800
Power stops.

FIG. 2 shows the photometric area of the light receiving element.

The light-receiving element 1 measures the light in the area A of the scene 35, and the light-receiving element 2 measures the light in the area B. In a front-lit scene, it is A2B, and in a back-lit scene, it is A(B), so 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 n degrees of area B, and is expressed using brightness value (BV) as a scale. When the brightness difference is less than zero BV, the scene is frontlit and the amount of strobe light emission is 30 times the reference value.

This means that the strobe light contributing to film exposure will be 30 degrees, which is the appropriate exposure amount. Brightness difference is 0 to 8B
Between V7-, the scene is weakly backlit, and the amount of light emitted by the strobe changes depending on the degree of backlighting. This change may be a linear change as in this embodiment, or may be a curved or stepwise change. When the brightness difference is 8 BV or more, there is strong backlighting, and in this case, the strobe light emission amount is 100%, and the strobe fires in the same way as when shooting with a strobe at night.

The present invention having the above-mentioned configuration is useful in daytime synchronized photography, since the strobe light control level depends on the lighting condition of the scene, so even if the main subject, which is likely to be in the center, is backlit, this can be adjusted. #l Appropriate exposure can be achieved.

[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. l ... Light receiving element 2 that measures the central part of the scene... Light receiving element -8 that measures the peripheral part of the scene -8 = 8... Light receiving element 7 that measures the average light of the scene... Differential amplifier 2021... -Comparator 28...Phototransistor 80 for measuring strobe reflected light...Flash discharge tube 81...Synchro switch.

Claims (3)

[Claims] (1) An automatic light control method characterized by measuring the brightness between the center and peripheral parts of a scene, and changing the light control level according to this difference in brightness during daytime synchronized shooting. (2) Based on the value of the brightness difference, it is classified into a forward light area, a weak backlight area, and a strong backlight area, and in the front light area, the strobe light emission amount is maintained at a first dimming level that is less than the reference value. In the strong backlight area, the strobe light emission amount is maintained at a second dimming level serving as a reference value, and in the weak backlight area, the body level is changed according to the difference in brightness. The automatic light control method described in Range 1. (3) In an automatic light control device that stops emitting light from a flash discharge tube when the integral value of the strobe reflected light reaches a light control level, a means for detecting the brightness in the center of the scene and a means for detecting the brightness in the peripheral part of the scene. means for inputting the output signals of these detection means and outputting a first signal corresponding to the luminance difference as the dimming level; a limiter piece for determining the maximum and minimum values of the first signal; An automatic light control device comprising: