Exposure controls for photographic copy machines

摘要

A photographic copying machine wherein copying light which issues from a light source and is directed toward an original is caused to pass through a light intensity weakening shutter of the venetian blind type. The shutter is adjusted to change the rate of passage of light therethrough in dependency on the intensity of signals which are generated by the exposure control system of the copying machine and denote the anticipated exposure times in the red, green and blue colors. If the anticipated exposure times are too short, the intensity of copying light which impinges upon the copying material is reduced by a stepwise adjustment of the venetian blind type shutter. Inversely, the shutter is caused to permit the passage of more light if the signals which are generated by the exposure control system denote a relatively long exposure times in the three colors. The switch-over from the higher intensity to the lower intensity takes place at lower density of the original than that corresponding to the switch-over in the opposite direction. An additional shutter is opened only with a delay corresponding to at least one-half the time period needed for adjustment of the venetian-blind shutter, in the event that such adjustment takes place.