For a single lens reflex camera in which an image bearing beam from the photographic objective is reflected by a movable mirror to the finder system, techniques are disclosed that the mirror is made half-reflective, and the transmitted light of the mirror is conducted by a supplementary optical member consisting of, at least, a prism fixedly secured (not movable relative) to the mirror toward an image sensor such as that of a focus detector positioned outside the optical axes of the objective and finder, that the movable mirror is made to take a quite different direction of movement from that to which the reflected beam from the mirror goes, and that as an image pickup device such as CCD is arranged on the optical axis of the objective and behind the movable mirror, the optical characteristics of optical members such as a filter positioned in front of the image pickup device are made equivalent to those of the supplementary optical member.