Abstract: In a flash photographing system including a camera having a light output control circuit for producing a stop of light emission signal when a light intensity of an illumination light reflected by an object reaches a predetermined level and a start circuit to start activation of the light output control circuit in response to a start of light emission signal, and a flash device electrically connected to the camera and having a flash bulb for emitting the illumination light, the flash device comprises detection means for detecting electrical connection with the camera, start of light emission signal generating means responsive to the detection means for supplying the start of light emission signal to the start circuit of the camera in synchronism with the emission of the illumination light by the flash bulb, and light emission stop means for stopping the emission of the illumination light by the flash bulb in response to the stop of light emission signal from the light output control circuit of the camera.

Abstract: An amplification factor selection circuit for an automatic light emission control circuit which enables selection of an amplification factor in accordance with an F-value, comprises a flash bulb for emitting a flash light to an object, a photo-sensor for sensing a light reflected from the object, an amplifier for amplifying the photo-current of the photosensor, a capacitor for starting charging upon emission of the flash light, a semiconductor device for controlling a charging current of the capacitor in accordance with an output of the amplifier, a light emission suppress circuit for suppressing the light emission when the capacitor is charged up to a predetermined level. A first reference voltage applied to the input terminal of the amplifier and a second reference voltage applied to the output of the transistor are relatively controlled. Two constant current sources are connected to opposite ends of a resistor and a point on the resistor is clamped to a predetermined potential.

Abstract: A control circuit for an electromagnetic shutter release mechanism for cinecamera controls a low level holding current at a predetermined constant level so that a shutter stopper which has been shifted in shutter operating position by an electromagnet energized by an initial high level actuating current is held in that position irrespective of a voltage variation of a D.C. power source.