Exposure servo-control device for cameras

Details Exposure servo-control device for cameras Exposure servo-control device for cameras

1978-11-22

1980-01-22

Gellner, Michael L.

Optics: motion pictures

Removable film strip magazine type

352141, G03B 708

Patent

active

041847571

ABSTRACT:
An exposure servo-control device for a camera prevents diaphragm overshoot by a simple damping construction including a mechanical switch or a semiconductor switching element which intermittently short-circuits a driving coil of an ammeter coupled to the diaphragm. A bridge circuit including a photoelectric element such as a CdS cell for receiving light flux from an object through the diaphragm aperture produces an output dependent on the deviation from an optimum aperture for the object to the presently positioned aperture. This output is amplified by an amplifier and input to the ammeter such that the driving coil drives the diaphragm to the optimum aperture. The damping of the diaphragm drive is caused by a counter-electromotive force generated in the driving coil each time the driving coil is short-circuited, and also by the inertia of movable portions of the diaphragm and the ammeter forced to stop during each period of time in which the driving coil is short-circuited. The period of time during which the driving coil is short-circuited may be controlled in accordance with the absolute value of the deviation, so that the greater the deviation, the shorter the period of time to enable faster adjustment of the diaphragm.

REFERENCES:
patent: 3421812 (1969-01-01), Kubota
patent: 3840295 (1974-10-01), Suzuki

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