Focussing system for still and motion-picture cameras

Details Focussing system for still and motion-picture cameras Focussing system for still and motion-picture cameras

1979-01-10

1981-11-10

Hix, L. T.

G03B 1318

Patent

active

042994675

ABSTRACT:
A single transducer is used to emit acoustic radiation towards the subject and receive the reflected-back radiation to generate a received-back signal. Upon emission, a switch becomes conductive to initiate charging of a timing capacitor, the charging terminating in response to the received-back signal. The capacitor charges through a variable resistor coupled to the focus adjuster, at a slower rate for longer subject-distance setting and at a faster rate for shorter subject-distance settings. Because the duration of capacitor charging is longer for longer actual subject distance, the voltage achieved by the capacitor at the termination of capacitor charging always has approximately the same value, no matter what the subject-distance setting, if the subject-distance setting is in fact correct, and thus this voltage constitutes a quality-of-focus signal. The latter signal is applied to one input of a subtractor whose other input receives a desired-quality-of-focus signal. The subtractor output signal is applied to two threshold stages, with neither threshold level exceeded when the setting is too long, both threshold levels exceeded when the setting is too short, and only one threshold level exceeded when the setting is acceptable. Two flip-flops are connected to respective threshold-stage outputs and are clocked by the received-back signal and respectively control two LED's, to indicate the sense of the focus error.

REFERENCES:
patent: 4103309 (1978-07-01), Massa
patent: 4199244 (1980-04-01), Shenk

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