GB1339718A - Electronic shutter control - Google Patents

Abstract

1339718 Photographic shutter control ASAHI KOGAKU KOGYO K K 22 Dec 1970 [25 Dec 1969 21 Feb 1970] 60932/70 Heading G2A An electronic shutter control circuit for use in a single lens reflex camera comprises a first circuit for effecting closed loop automatic control and composed of a photo-sensitive element Cds, a transistor Q 5 containing the transistor in its collector circuit, and an amplifier Q 4 containing a storing circuit C m for providing a voltage output proportional to the APEX index number B r of the brightness of the object to be photographed, a second circuit composed of a variable resistor V R and logarithmic conversion elements D 2 for obtaining a voltage output which is proportional to the algebraic sum (A v -S v ) of the APEX index numbers A v and S v of the diaphragm value and film sensitivity respectively, each of the first and second circuits being coupled to one of two transistors Q 7 , Q 8 which are symmetrically emitter-coupled with each other, so that photographic computation according to the APEX system can be performed, and a third circuit for obtaining in one of the two transistors a timing current T t corresponding to the T v value resulting from the computation, the timing current then being constant-current charged into a timing capacitor C t and the time period required for the voltage across the timing capacitor to reach a preselected value being used in determination of exposure time. A transistor Q 6 is coupled in parallel with the photo-sensitive element to form a by-pass circuit therefore when the difference between the reference voltage V o and the controlled voltage V 5 reaches above the threshold voltage of the transistor so as to stabilise operation.