DETECTING DEVICE FOR QUANTITY OF PHOTODETECTION

摘要

PURPOSE:To prevent a decrease in the reliability of color discriminating ability by providing a filter on the optical path between a body to be detected and a photodetecting element and making the quantity of photodetection of the photodetecting element constant regardless of variation in the distance between a light generating means and the body to be detected. CONSTITUTION:The filter 8 which varies in transmissivity in the direction of the movement of an irradiated area on the photodetecting element 6 when the body 2 to be detected move close or away along the optical axis 16 of a lens 5 is provided on the optical path of a photodetection quantity detecting element 1 between the body 2 to be detected and the photodetecting element 6. Then when the body 2 to be detected which is at specific distance l1 from the lens 5 moves close or away as shown by 2a or 2b and the irradiated area on the photodetecting element moves, the transmissivity of the filter 8 varies and the quantity of photodetection of the photodetecting element 6 becomes constant. Consequently, a decrease in the reliability of the color discriminating ability is prevented.