Circuit for preventing false operation of an electronic camera shutter

Claim 1

A circuit for preventing false operation of an electronic shutter of the type employed in a through-the-lens camera, which comprises, in combination: a d.c. source; an integrating circuit, connected to said source, and including: a capacitor; a photoelectric element serially connected to said capacitor, said element receiving light from the object to be photographed through the lens of said camera; a transistor, the base thereof being connected to the juncture of said capacitor and said photoelectric element, and; switching means for establishing a reference time interval of conduction in said transistor, as determined by charging of said capacitor through said photoelectric element when said switching means is closed, said reference time interval being representative of the intensity of the light received by said photoelectric element, and determined by the time constant of said capacitor and said photoelectric element, said transistor conducting only when the voltage developed across said capacitor exceeds the threshold voltage thereof; a memory circuit, connected to said integrating circuit, and enabled by closure of said switching means during said reference time interval, for generating a reference voltage therein which corresponds to the intensity of light received from said object; an exposure control circuit, connected to said memory circuit and actuated simultaneously with the opening of the shutter blades of said camera, for generating a time-varying voltage; a switching circuit, connected to said exposure control circuit, for closing said shutter blades when said time-varying voltage reaches a predetermined level, with respect to said reference voltage, so as to obtain the proper exposure time for said shutter, in accordance with the intensity of light received from said object; and diode means, connected in said serial connection of the capacitor and photoelectric element in said integrating circuit, to inhibit discharge of said capacitor, and hence an erroneous reference time interval, due to chatter of the contacts in said switching means.