| 摘要 |
PURPOSE:To remove the shading of light flux, to surely detect a focus and to prevent low brightness detecting capacity from being deteriorated by inserting an optical member for reducing an opening angle of detected light flux without changing the size of an aperture part of an image reforming lens into an image reforming optical system. CONSTITUTION:The optical member 101 is freely attachably/detachably arranged between a focus detecting face 107 and an image reforming lens 102 and the member 101 is provided with lens systems 101a, 101b for reducing a detected opening angle theta' from a detected opening angle theta of a pair of detected light beams 108a, 108b obtained before loading the optical member 101 without changing the size of a pair of aperture parts of the lens 102. Since the detected opening angle on the photographing lens side can be varied by attaching/detaching the optical member 101, unevenness or vignetting is not generated in a pair of detected light beams which may be generated by a variable diaphragm like an ordinary case. Since the aperture diameter of the image reforming lens is not changed by a fixed diaphragm even if the detected opening angle is reduced by loading the optical member, a low brightness lamination capable of detecting a focus is not deteriorated. |
