Photocopying – Projection printing and copying cameras – Illumination systems or details
Patent
1991-07-31
1992-12-08
Gellner, Michael L.
Photocopying
Projection printing and copying cameras
Illumination systems or details
355 77, G03B 2780
Patent
active
051702088
ABSTRACT:
An exposure control apparatus for a microfilm printer includes an area (planar) light source, photo detector, and digital control circuits. An averaged density reading over at least the central five to twenty percent of the area of the microfilm frame is measured. This density reading is then used to control the intensity of the exposure lamp via a digital control circuit. The spatial relationships between the elements of the light source, the microfilm frame being read, and the photodetector are optimally arranged to provide an even illumination of the portion of the microfilm frame being measured without interfering with the film exposure process and without creating undue space demands.
The microfilm density measurement provided by the apparatus is used to automatically control the intensity of the exposure lamp used in the exposure of a light sensitive medium in the development of prints from the microfilm. The exposure lamp light intensity that corresponds to the threshold level of the light sensitive medium (the minimum light exposure level that will form an image with no film in the exposure station) is established as the zero density threshold intensity. A threshold offset that corresponds to the measured density of a microfilm frame to be printed is added to the zero density threshold intensity to establish a desired exposure lamp intensity for exposing the microfilm frame for printing.
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Koehler Bruce H.
Owen Richard
Gellner Michael L.
Griswold Gary L.
Kirn Walter N.
Linder Walter C.
Minnesota Mining and Mannufacturing Company
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