Through-the-lens exposure control for SLR camera - has integral photocell and condenser lens to measure light reflected off film through half-silvered mirror

摘要

Through the lens exposure control for an SLR camera has a photocell (4) in the bottom of the camera case to monitor light reflected off the film (12). The light is focussed onto the photocell by an integral condenser lens (3) positioned not to interfere with the exposure of the image. In the viewing position part of the light passes through a half silvered section of the viewing mirror and is reflected into the photocell by a small mirror (11) behind the viewing mirror, both mirrors are swung aside for exposure. In the exposure position, the photocell accepts diffuse reflected light from the top part of the film and more directly reflected light of the lower part. The exposure circuit makes correction between the two modes of measurement so that a continuous exposure factor is provided during the exposure cycle.