| 摘要 |
PURPOSE:To detect an out-of-focus state with a high gain by applying photoelectric conversion to the light within a center region of the light transmitted through an objective, and to the light within a circular region around said center region, and detecting a relative position error between the focal point of the objective, and to the surface of a subject, from the relationship between the output signals of both regions. CONSTITUTION:The parallel luminous fluxes delivered from a light source 1 are reflected by a semitransparent mirror 2 and irradiated to a medium 4 via an objective lens 3, and this reflected light is sent to a photodetector 5 via the lens 3 and the mirror 2. The luminous intensity distribution on the detector 5 is symmetrical centering on an optical axis Z. The energy received at a circular photodetecting part PD2 is equal to the value E1 obtained by integrating the luminous intensity distribution covering from radius O through R1. While the energy of a circular photodetecting part PD1 is equal to the value E2 obtained by integrating the luminous intensity distribution ranging from radius R2 through R3. The luminous intensity distribution varies in accordance with the distance between the focal point F of the lens 3 and the surface of the medium 4, i.e., the out-of-focus degree (e). The output proportional to the value of (e) is obtained by calculating E1-E2. Thus an out-of-focus degree can be detected. |
