| 摘要 |
PROBLEM TO BE SOLVED: To make obtainable high position detecting accuracy, even when the distance between a light projector and a photodetector R is changed in the photodetector R, which detects the light receiving position of a reference light projected from the light projector of a rotating laser device L or the like. SOLUTION: Two rectangular photodiodes 21, 22, which are long in the longitudinal direction as a measuring direction, are arranged in the transverse direction to form one set, and four sets are arranged in the longitudinal direction at the light-receiving window part 2 of the photodetector R. A light and shade light adjusting filter 24 which covers them is divided into eight sections, so as to correspond to the respective photodiodes 21, 22. The respective sections, corresponding to the photodiodes 21 on the left side as viewed from the front, are set in such a way that their optical densities become gradually lower toward the lower side, starting from the upper side. The respective sections corresponding to the respective photodiodes 22 on the right side as viewed from the front are set, in such a way that their optical densities become graually higher toward the lower side, starting from the upper side.
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