Compensated electrically controlled focal plane shutter

Claim 1

An electrically controlled focal plane shutter for a camera, comprising: a first curtain movable from a cocked position to a rest position for initiating film exposure; a second curtain movable from a cocked position to a rest position for terminating the film exposure, the trailing edge portion of said first curtain and the leading edge portion of said second curtain overlapping one another with said first and second curtain in said cocked positions; an electric power source; means for releasing said second curtain from said cocked position after a time delay; an electric timing device for determining said time delay and controlling said means for releasing and including; a variable resistor; a capacitor connected in series with said variable resistor; an adjustable compensating resistor connected in series with said variable resistor and said capacitor for adding a time lapse delay to said time delay for compensating exposure errors caused by the overlapping of said first and second curtains in said cocked positions, the resistance r of said adjustable compensation resistor is adjusted in accordance with the following formula: where C is the capacitance of said capacitor, E is the voltage of said power source, V1 is the voltage at the junction of said capacitor and said compensation resistor, and to is a time delay equivalent to the overlapping of said first and second curtains; and a switching circuit responsive to said set voltage.