Optics: measuring and testing – Photometers – Photoelectric
Patent
1973-08-03
1976-10-26
Miller, Charles D.
Optics: measuring and testing
Photometers
Photoelectric
340347AD, G01J 142
Patent
active
039880699
ABSTRACT:
This invention relates to an automatic camera exposure control device comprising a first light measuring circuit including a photoelectric element receiving light through the objective lens of the camera and generating a first output proportional to the logarithm of the brightness of an object to be photographed, and a circuit for providing a second output indicative of the film sensitivity and the lens aperture value, the light measuring circuit for providing a first signal indicative of the sum of the first and second outputs; and a second circuit including a pulse generator circuit for generating clock pulses and a counter for counting the clock pulses and for producing a second signal of a stairstep waveform corresponding to the counting of a pulse; a voltage comparator circuit for comparing the second signal with the first signal and for producing a signal when the level of the second signal exceeds that of the first signal; a third circuit composed mainly of a gate circuit for stopping the counting of the pulse upon receipt of the threshold level signal from the voltage comparator circuit; and a shutter control circuit including a transistor for inverse logarithmic conversion and for producing a collector current proportional to the exponent of the second signal applied to its base, and a capacitor to be charged by the collector current of the transistor and a switching circuit responsive to the voltage charged in the capacitor in excess of a predetermined level for actuating the shutter to terminate the exposure interval.
REFERENCES:
patent: 2968744 (1961-01-01), Kroupa
patent: 3022944 (1962-02-01), Stuart
patent: 3441723 (1969-04-01), Reidel
patent: 3568179 (1971-03-01), Lampkin
patent: 3594683 (1971-07-01), Ihaya
patent: 3747089 (1973-07-01), Sharples
patent: 3781872 (1973-12-01), Frye
Miller Charles D.
Minolta Camera Kabushiki Kaisha
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