SELF-BALANCING APPARATUS FOR PHOTOGRAPHIC CAMERAS

摘要

A self-balancing exposure control apparatus is disclosed which includes a diaphragm defining a first aperture disposed in a cooperative relation with a camera lens and a second aperture disposed in a cooperative relation with a photosensitive device having a parameter which varies as a function of incident illumination. The apparatus includes a control circuit which responds to variations in the parameter to move the diaphragm to adjust the effective size of the respective apertures to return the level of illumination incident on the photosensitive device to a predetermined level wherein the circuit is balanced and pass sufficient light to the camera lens for suitable film exposure. With decreasing scene brightness, the control circuit causes the diaphragm to increase the effective size of both apertures until the camera lens aperture reaches a size which corresponds to the maximum light transmitting capability of the camera lens. If the scene brightness continues to decrease, the size of the camera lens aperture will be maintained at the maximum size while the photosensitive device aperture will continue to increase in size to return the illumination incident on the photosensitive device to the predetermined illumination level.