Exposure control circuit

Details Exposure control circuit Exposure control circuit

1975-07-15

1977-02-08

Adams, Jr., Russell E.

354 60R, 354 60A, G03B 708

Patent

active

040074676

ABSTRACT:
A light-sensitive element is connected to a capacitor to vary the charging rate of the capacitor in accordance with the light falling on the light-sensitive element. The emitter-collector circuit of a switching transistor is connected in series with the light-sensitive element. The base of the transistor is pulsed by an astable multivibrator which furnishes a pulse sequence having a pulse repetition rate which exceeds the reciprocal of the smallest exposure time. The pulses in the pulse sequence have a pulse width determined by the selected one of a plurality of resistors. The selector switch inserting the selected one of the resistors into the astable multivibrator circuit is coupled to selector means which select one of a plurality of exposure factors as for example the aperture size. The electronic switch is conductive, permitting charging of the capacitor only during the pulse duration. The charging rate of the capacitor can therefore be adapted to the particular aperture size, film sensitivity, etc. without changing the capacitance of the capacitor or covering a portion of the light-sensitive element.

REFERENCES:
patent: 3460451 (1969-08-01), Stamp et al.
patent: 3711721 (1973-01-01), Hausen
patent: 3868704 (1975-02-01), Yamada et al.
patent: 3879118 (1975-04-01), Kiyohara et al.
patent: 3882510 (1975-05-01), Dobusawa

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