| 摘要 |
PROBLEM TO BE SOLVED: To restrain influence of spherical aberration of a pupil when the surface displacement of a surface having an angle of gate is sensed, by constituting the distortion amount of a light receiving side objective optical system to be small by a specific ratio to the width of a light receiving slit. SOLUTION: A vibration mirror 41 is added to a part between an object side lens system 30 and an image side lens system 31, so that optical members in front of the image side lens 31 are arranged in the reflection direction of a light of the vibration mirror 41. A light receiving slit S2 is formed on a light receiving surface 32. A light sending slit S1 on a light sending slit surface 27 and the light receiving slit S2 have nearly equal width. The width for vibrating a beam on the light receiving slit S2 is based on the same value as the slit width, so that distortion D is made smaller than the slit width, from dynamic range viewpoint. Desirably, D is less than or equal to 3/8 of the slit width. More desirably, D is less than or equal to 1/4 of the slit width. |
