Photocopying – Projection printing and copying cameras – Illumination systems or details
Patent
1979-06-26
1981-11-24
Miller, Jr., George H.
Photocopying
Projection printing and copying cameras
Illumination systems or details
355 83, 356443, G03B 2780
Patent
active
043020992
ABSTRACT:
A Programmable Computing Enlarging Exposure Meter determines printing and contrast grades and shadow speeds and contrast grades of photosensitive material measuring printing density and contrast of film in its light path, with its unique analog computer it determines the necessary contrast grade and the exposure time required to produce a print of the necessary density. All computations and determinations are performed internally without requiring user extrapolating in the dark with calculator dials and attached slide rules that are the practice with instruments designed for the purpose.
The structure comprises a power supply, light measuring device, a light to voltage converter for converting the light measurement to one or more linearly proportional voltages having range of 1:10 between them.
An operational amplifier produces fixed output voltage. An R.sub.1 inverting input variable log taper resistor calibrated against the paper speed and paper grade scales on the front panel, an R.sub.f variable log taper resistor connected between the output of the operational amplifier and the junction of the inverting input and R.sub.1, and is linearly calibrated to the exposure time scale associated with the panel of the meter. Resistor R.sub.1 connects the operational amplifier to the output of the light to voltage converter.
Since the operational amplifier produces a fixed output voltage, R.sub.1 and R.sub.f are used against each other for accurate multiplication and division. The meter announces completion of measurements and calculations in process, by the fixed voltage output of the operational amplifier triggering and latching a thyristor circuit, which energizes an annunciator L.E.D. The results of the process is now read against the appropriate panel scale.
REFERENCES:
patent: 3874793 (1975-04-01), Nielsen
patent: 4199252 (1980-04-01), Vermeulen
Brady W. J.
Gewirtz Stanley J.
Miller Jr. George H.
Wein Fredrick A.
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