| 摘要 |
PURPOSE:To uniform and reduce errors without reference to measured distance by providing a variable density filter which varies the quantity of passing light and a slit which varies in opening width in the density variation direction in the image formation space of an objective system. CONSTITUTION:Light emitted by a light emitting element 2 reaches the objective system 1 through a triangular prism 5, an oblique mirror 6, and an optical path 8 of transmission and its reflected light from an object of measurement reaches a photodetecting element 3 through an optical path 7 of photodetection. The variable density filter 9 which varies the quantity of passing light is interposed between the prism 5 and oblique mirror, 6 and the slit stop 14 which has its opening extended in the density variation direction and increases in opening width with the density is added. The quantity of measurement light is adjusted with the density of the filter 9 and the opening extent of a slit opening part 14a and the measurement luminous flux can be limited to the center part of the image space of an objective, specially, during short-distance measurement errors are uniformed and reduced without reference to the measured distance.
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