Focus detecting optical system including eccentrically disposed aperture stops

摘要

A focus detecting optical system comprises two imaging optical systems which are composed of an integrally molded prism, and is adapted to perform focus detection on the basis of relative positional relationship between an image of an object formed with one of the imaging optical systems and another image of the object formed with the other imaging optical system. Ineffective optical path regions of the surfaces of the prism which allow transmission or reflection of the rays entering the prism are designed as light diffusing surfaces and/or surfaces coated with a light absorption substance. An aperture stop arranged before each surface of incidence of light is arranged eccentrically with regard to the optical axis of incident rays or each surface of incidence of light has a refractive power asymmetrical with regard to said optical axis so that all the rays incident on the totally reflecting surfaces arranged in the two imaging optical systems are totally reflected. The integrally molded prism can comprise a plurality of pairs of the imaging optical systems. This focus detecting optical system can be manufactured at a low cost, has a high distance measurement accuracy and requires substantially no mutual matching for optical elements used therein.