| 摘要 |
PROBLEM TO BE SOLVED: To provide a focal point detector capable of surely shielding diffracted light beams and scattered light beams which are harmful to focal point detecting. SOLUTION: In this focal point detector, a pattern 3 or a light source image is projected on a material 8 through an objective lens 7, the pattern or the light source image reflected from the material 8 is guided to the lens 7 again, plural times of image formation 21 and 23 are performed by the lens 7 and a succeeding optical system 11, a photodetector 14 is arranged on a final image formation surface 23, and a detection side light shielding board 12 formed asymmetrically with respect to an optical axis is arranged between the image formation surfaces 21 and 23 adjacent to each other among the image formation surfaces subjected to plural times of image formation, so that a luminous flux reaching the photodetector 14 is partially shielded. In this case, the board 12 is arranged on the pupil conjugate image position 22 or a position in the vicinity of the position 22. |
