| 摘要 |
PURPOSE:To convert a focus detecting speed to a high speed by constituting plural focus detecting optical systems in symmetrical positions of an optical axis of an objective lens. CONSTITUTION:A visual field mask 101, a field lens 102, a diaphragm 103 and a secondary image forming lens 104 are placed in said order, on an optical axis of an objective lens. The visual field mask 101 has a cross-shaped through- hole, and controls an air image of an object to be photographed, which has formed an image by the objective lens 106. The field lens 102 projects the dia phragm 103 to an exit pupil 108 of the objective lens 106, and sets the dia phragm 103 and the exit pupil 108 to a conjugate relation. The diaphgram 103 has four pieces of fan-shaped opening parts 103a-103d for setting the optical axis as a point symmetry, and the exit pupil 108 of the objective lens 106 is divided into four pieces of areas 108a-108d. The secondary image forming lens 104 has four pieces of lens parts 104a-104d corresponding to four pieces of opening parts 103a-103d of the diaphragm 103, and a visual field mask image 109 is formed on a photoelectric converting element 105 which has been placed in the rear side of the secondary image forming lens 104. |
