| 摘要 |
PURPOSE:To realize a focal point detecting device capable of high precision focal point detection which prevents unnecessary light incidence on a photodetector plane and causing ghost light by arranging two light limiting members which limit luminous flux within a certain optical path. CONSTITUTION:Plural light quantity distributions related to an object image are formed by using luminous flux which passed through the regions of different pupils on an objective lens 1, the relative positional relationship of the light quantity distributions are obtained by a light receiving means 5, and the focusing condition of the objective lens 1 is detected. Since a visual field mask 2 and a light shielding mask 24 are positioned respectively just before the field lens 3 and the light receiving means in the optical path from the objective lens 1 to the light receiving means 5, the unnecessary luminous flux incident on the peripheral area on the planes of the photodetector strings 5-1 and 5-2 is interrupted among the relatively widely set luminous flux from the visual field mask 2. Therefore, the minimum necessary luminous flux is incident on the photodetector strings, the ghost light caused by the multiplex reflection from the surface of a resin member 18, etc., is decreased, and the high precision focal point detection is realized. |
