Electronic shutter control circuit having exposure time indicator

Claim 1

A control circuit for a camera shutter, comprising: a Schmitt trigger circuit including an input stage comprised of a first transistor and an output stage comprised of a second transistor having an emitter and a collector; means for applying a brightness signal having a magnitude proportional to a brightness of a scene to be photographed to said first transistor and for applying an exposure time signal having a duration determined by the brightness of a scene to be photographed to said first transistor, said brightness signal having a magnitude less than a certain threshold value when the brightness of the scene to be photographed is less than a certain value to render said first transistor non-conductive and thereby render said second transistor conductive, and said exposure time signal having a magnitude less than said certain threshold value for a period of time equal to an exposure time determined by the brightness of the scene to be photographed thereby to render said second transistor conductive during said exposure time; an electromagnet connected to the output stage of said Schmitt trigger circuit and energized when said second transistor is rendered conductive, whereby said electromagnet is deenergized upon completion of said exposure time; and an indicating device connected to said emitter of said second transistor to define an emitter impedance of said Schmitt trigger circuit output stage and energized to indicate when said second transistor is conductive, whereby said indicating device indicates when the brightness of the scene to be photographed is less than said certain value during the occurrence of said brightness signal, and indicates when said electromagnet is energized during said exposure time signal.