Circuit for the control of exposure time in photographic enlargi

Details Circuit for the control of exposure time in photographic enlargi Circuit for the control of exposure time in photographic enlargi

1979-07-25

1981-08-25

Griffin, Donald A.

Photocopying

Projection printing and copying cameras

Illumination systems or details

355 38, 355 55, G03B 2780

Patent

active

042855934

ABSTRACT:
In a circuit for the control of exposure time with photographic enlarging equipment with variable enlargement ratio, and with a device for determining light quantity, a light sensitive electric transducer is provided a fixed distance to the negative plane of the enlarging equipment. Means for generating a signal representing the enlargement ratio, in the form of a potentiometer, modifies the signal derived from the device for determining light quantity to thereby produce a signal representative of the proper change of exposure time for a selected enlargement ratio. The circuit incorporates function generators to modify the signal from the light sensitive electric transducers to allow for the correction of the failure of the reciprocity law. The light sensitive electric transducer is in the form of a photodiode, and the signal derived therefrom as a result of determining light quantity produces a charge on a capacitor which develops a signal, in one embodiment, that is compared in a comparator with the potentiometer signal.

REFERENCES:
patent: 3884576 (1975-05-01), Mochimaru et al.
patent: 4017180 (1977-04-01), Yen et al.
patent: 4020495 (1977-04-01), Ebner et al.
patent: 4113378 (1978-09-01), Wirtz

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