Cameras with electrically controlled exposure for use with elect

Details Cameras with electrically controlled exposure for use with elect Cameras with electrically controlled exposure for use with elect

1976-11-17

1978-09-05

Hix, L. T.

354 33, 354128, G03B 1505

Patent

active

041124421

ABSTRACT:
A camera having an electrically controlled exposure is capable of mounting thereon or incorporating therein an electronic flash device which includes a flash tube, a main capacitor for firing the flash tube and a trigger circuit having a trigger capacitor. To initiate the flashing of the flash tube, the trigger capacitor, which has been charged to a voltage level corresponding to that across the main capacitor, is discharged in synchronism with the opening of a shutter through a firing circuit which is made conductive only when the brightness of an object is lower than a predetermined level. A first transistor is made conductive upon the opening of the shutter only when the brightness of the object is lower than the predetermined level and a second transistor is connected in series with the first transistor and made conductive only when the trigger capacitor is charged up to a sufficient level. The series connection of the first and second transistors is in turn connected to a time constant circuit consisting of a timing capacitor and a photoconductive element for detecting the brightness of the object. The timing capacitor is rapidly charged or discharged to a predetermined level when both the first and second transistors are made conductive, so that an exposure control circuit connected to the timing capacitor generates a signal for terminating an exposure soon after the flashing of the flash tube.

REFERENCES:
patent: 3690237 (1972-09-01), Fuwa
patent: 3978496 (1976-08-01), Matsumoto
patent: 4016575 (1977-04-01), Uchiyama et al.

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