| 摘要 |
PURPOSE:To improve a deviation in range measured value and a range finding time at a long range side by providing a light quantity monotonous increase section wherein the quantity of transmitted light is increased monotonously according to an increase in measured range to both light quantity controllers for range finding light and reference light. CONSTITUTION:A rotation density filter 10 is provided with annular filters 11 and 12 internally and externally; the reference light is passed through the internal annular filter 11 and range finding light is passed through the external annular filter 12. The annular filter 12 has a light quantity monotonous increase section 12i wherein the quantity of transmitted light increases monotonously between a 0 deg. and a 240 deg. position and the annular filter 11 has a light quantity increase section 11i wherein the quantity of transmitted light increases monotonously between a 0 deg. and a 240 deg. position. Thus, the level of the quantity of light incident on a photodetecting element is increased only in the measurement area up to an area where the measured range attains to a constant value, so the deviation in measured range and range measuring time are improved, specially, at the long range side.
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