Focusing optical system for single-lens reflex cameras

摘要

A focusing optical system for single-lens reflex cameras comprising a quick return mirror having a section of incidence formed by removing a portion of the surface of said mirror and an emerging section, and a detector element which is arranged in the vicinity of said section of incidence. Said focusing optical system is adapted in such a manner that a portion of the light emitted from an object to be photographed is allowed to pass through said section of incidence into the inside of said quick return mirror, reflect on the inner surfaces of said quick return mirror, emerge from said emerging section and then is detected with said detector element, thereby permitting accurate detection without hindering observation through a finder of single-lens reflex cameras.