Warning circuit for use in a ttl-type electronic shutter

Claim 1

Warning circuit for use in a TTL-type electronic shutter for warning the inappropriate condition of the scene brightness for the proper exposure, said electronic shutter consisting of an electric source, an integrating circuit having a photoelectric element receiving the light from the object through the objective of a camera, a first capacitor connected in series to said photoelectric element and a transistor with its base connected to the junction of said photoelectric element and said first capacitor, and supplied with the emitter bias by said electric source, a memory circuit having an electrical resistaNce element such as a photoelectric element and a resistor, a second capacitor connected in series to said electrical resistance element and a transistor with its base connected to said integrating circuit, and an automatic exposure control circuit, said first capacitor being charged through said photoelectric element until said transistor in said integrating circuit is made conductive, the time during which said capacitor is charged being a reference time set in accordance with the intensity of light from the object, said second capacitor being charged or discharged during said reference time through said electrical resistance element until said transistor in memory circuit is rendered to be nonconductive by the switching of said transistor in said integrating circuit so as to provide a reference voltage in said second capacitor indicative of the intensity of the light, said reference voltage being utilized in obtaining the proper exposure by said exposure control circuit, wherein the improvement comprises a series circuit of a resistor and a capacitor with said resistor connected to said transistor of said memory circuit and with said capacitor connected to one terminal of said electric source, a first transistor with its base connected to the junction of said resistor and said capacitor and with its emitter supplied with an emitter bias by said electric source, a second transistor with its base connected to the collector of said first transistor, and pilot means such as a lamp with it one terminal connected to the collector of said second transistor while the other terminal of said pilot means is connected to said one terminal of said electric source, the emitter of said second transistor being connected to the other terminal of said electric source, the time constant as set by said series circuit and the emitter bias of said first transistor for rendering said first transistor to be conductive being determined so as to correspond to one of the upper limit of the shutter speed and the lower limit of the shutter speed beyond which blurring of the photograph might occur, thereby permitting the inappropriate condition of the scene brightness for the proper exposure to be determined by the energization or the deenergization of said pilot means.