| 摘要 |
PURPOSE:To attain highly accurate focus position detection over a wide defocusing range wherein the quantity of defocusing is large by properly setting respective elements for making eccentric luminous flux incident on an image formation optical system and respective elements such as an auxiliary detector. CONSTITUTION:A light limiting member 91 has a reflecting surface which reflects reflected light from a surface to be inspected and directs it to a photodetector 7, the auxiliary photodetector 3 detecting part of the reflected light from the surface to be inspected which does not strike on the photodetector 7 by passing by the reflecting surface is arranged, and the position of the surface to be inspected in the direction of the optical axis 114 is adjusted according to the signal from this auxiliary photodetector 3. Then when a body 92 is large and in a defocusing state, a driving means 40 moves and adjusts the body 92 or image formation optical system 9 and then the reflected luminous flux from the body 92 is made incident on the photodetector 7, which outputs a specific difference signal. Consequently, the focus position of the image formation optical system 9 can be detected with high accuracy over the wide range. |
