| 摘要 |
PURPOSE:To decrease an error factory by separating an image of a light spot of the surface of an object by a half mirror, and specifying a transmittivity distribution of space filters installed at this side in one optical path, and at the rear side in the other optical path, respectively, with respect to said image. CONSTITUTION:A luminous flux of a light source 1 is made incident on an object surface 6 through lenses 3, 4 and from its reflected light, an image of a light spot is formed at two points by a half mirror 7, an image forming lens 8 and a half mirror 9, and with respect to its image, space filters 20, 21 are provided at the same distance at this side in one optical path, and at the rear side in the other optical path, respectively, and photodetecting is executed by photodetectors 12, 13. In that case, a transmittivity distribution of the filters 20, 21 is made approximate to a Gaussian curve which is high in its optical shaft center and decreases continuously and becomes zero as it goes to the periphery, and even if an error factor of a spherical aberration, etc. is generated, the output is not varied suddenly. |
