Light-measuring systems for single lens reflex cameras

Abstract

A single lens reflex camera has behind its objective a main mirror for reflecting light up to the viewfinder. This main mirror has a semitransparent portion through which part of the light which has traveled through the objective passes. Behind the semitransparent portion of the main mirror is an auxiliary mirror for receiving the light which has passed through the semitransparent portion of the main mirror and for reflecting this light along a predetermined path. A photosensitive device is situated along the latter path to receive the light reflected by the auxiliary mirror and to participate in the measurement thereof. The main mirror has at its semitransparent portion a front surface from which part of the light which has traveled through the objective is reflected up to the viewfinder and a rear surface beyond which part of the light travels to the auxiliary mirror. The auxiliary mirror has a front reflecting surface from which the light is reflected along the predetermined path to the photosensitive element. This rear surface of the main mirror and the front reflecting surface of the auxiliary mirror form a pair of surfaces one of which has the property of diffusing light, so that the photosensitive element receives diffused light.