GB1162474A - Time Control Circuit in Electronic Shutters. - Google Patents

Abstract

1,162,474. Electronic shutter control device. KONISHIROKU PHOTO INDUSTRY CO. Ltd. Jan. 25, 1968 [Jan. 26, 1967; March 16, 1967; March 25, 1967 Nov. 22, 1967], No.4043/68. Heading G1A. [Also in Division G2] An electronic shutter of a photographic camera includes a time control circuit comprising a photo-voltaic cell exposed to the taking light, the cell output being applied to the emitter of a grounded base transistor having a D. C. supply and a capacitor in series in its base-collector path, means for discharging the capacitor and means responsive to a predetermined voltage on the capacitor to provide a shutter closing signal. In one embodiment, Fig.1, for use with a flashlight, closing of a shutter release (not shown) closes a switch S 2 to energize an electromagnet M to open the shutter, and a switch S 1 is simultaneously opened so that a capacitor C is charged by the output of a grounded base transistor T 1 , whose input is the voltage of a photo-voltaic cell P, and at a predetermined voltage corresponding to the required exposure time, a transistor T 2 is triggered, in turn triggering a transistor T 3 , cutting off transistor T 4 , de-energizing electromagnet M, and closing the shutter. A variable resistor R adjusts the triggering voltage to allow for variation in film speed. In a modification Fig. 2 (not shown) batteries E 1 , E 2 are replaced by a single battery (E) having the variable resistor (R) connected across its terminals. In another embodiment Fig. 3 (not shown) the photo-voltaic cell (P) with capacitor (C 1 ) or a photo-conductor (Cds) with a series capacitor (C 2 ) is selectively switched by a switch (S 3 ) to the trigger transistor (T 2 ) for flash-light or low intensity light respectively. In another embodiment Fig. 4 (not shown), the photoconductively controlled capacitor feeds a second transistor T 2 <SP>1</SP> whose output is parallel with that of T 2 controls T 3 , the arrangement being such that the output from T 2 <SP>1</SP> predominates over that of T 2 or vice versa according as the illumination is low-level or high-level as in flash; a high resistance (R 1 ) shunts capacitor (C 1 ) to prevent unstable operation of the latter.