Focus detecting optical device of a single lens reflex camera

Abstract

This specification discloses a focus detecting optical device for photoelectrically effecting focus delection by the use of two restricted light beams passed through different areas in the pupil of a phototaking lens in a single lens reflex camera including a finder screen capable of imaging the light beam from the phototaking lens and a pentaprism having reflecting surfaces capable of reflecting a light beam passed through said screen toward an eyepiece lens system having an optical axis substantially orthogonal to said screen. The optical device is provided with light splitting means for splitting a light beam in a direction substantially parallel to the optical axis on that side on which the eyepiece lens system is positioned from a light beam passing from the finder screen to the first reflecting surface of the pentaprism, light distributing means for distributing the split light beam in two directions to provide the two restricted light beams, a first and a second detecting lens system disposed in opposed relationship with each other for receiving the two restricted light beams distributed by the light distributing means, first and second direction changing means for directing the lights passed through the first and second detecting lens systems in directions passing through the opposite sides of the eyepiece lens system, and a first and a second photoelectric conversion element provided at positions capable of receiving the lights directed by the first and second direction changing means.