Proper focusing state detecting device

摘要

A device for automatically detecting a proper focusing state of an image-forming optical system e.g. for a photographic camera such as a single-lens reflex camera and the like, comprises a mechanism for splitting a beam of light incident through the optical system. The device does not depend intrinsically upon a current state of polarization of the incident light-beam.PPThe mechanism for splitting a beam of light comprises a two-component lens arrangement which divides the incident beam of light into two beams of light, and a phase-shifting plate behind one of the components for lengthening the effective optical path of one of the split beams with respect to the other split beam. A first a second array of light-sensing elements is provided for receiving both of the split beams of light for evaluating and comparing the sharpness and other characteristics of the two beams of light.