Density measuring device for originals in an enlarging/reducing projector

摘要

A density measuring device for originals in an enlarging/reducing projector, which is installed in a electrophotographic copying machine or in an image sensor to measure original densities for enlarged/reduced printing under automatic exposure control. The device includes a light sensor, which receives light from an original via mirrors, and moves to keep a constant distance between the sensor and the original when the mirrors move in response to the change of projective magnification. The length of optical path for original density measurement is corrected by moving the sensor separately from but in accordance with the projection lens as the lens moves to change projective magnification.