Automatic exposure control apparatus for a microfilm printer.

摘要

An exposure control apparatus 10 for a microfilm printer 12 includes an area (planar) light source 50, photo detector 52, and digital control circuits 54. An averaged density reading over at least the central five to twenty percent of the area of the microfilm frame 36 is measured. This density reading is then used to control the intensity of the exposure lamp 24 via a digital control circuit. The spatial relationships between the elements of the light source 50, the microfilm frame 36 being read, and the photodetector 52 are optimally arranged to provide an even illumination of the portion of the microfilm frame 36 being measured without interfering with the film exposure process and without creating undue space demands. The microfilm density measurement provided by the apparatus 10 is used to automatically control the intensity of the exposure lamp 24 used in the exposure of a light sensitive medium 36 in the development of prints from the microfilm. The exposure lamp 24 light intensity that corresponds to the threshold level of the light sensitive medium 36 (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 36 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. <IMAGE>