| 摘要 |
PURPOSE:To reduce a photodetecting sensitivity difference in infrared rays due to a distance, and to reduce a level difference in a human body detecting signal due to the distance, by rotating a visual field surface formed by a slit whose opening width is widened as it is placed away from the rotation center. CONSTITUTION:A circular scanning optical system 1 is provided with a slit X whose opening width is widened as it is placed away from the rotation center, and by rotating a visual field surface formed by this slit X, a visual field of an infrared ray detecting element 2 is scanned circularly. When this slit X is placed in front of a cylindrical mirror M, as for a level of a signal obtained by the infrared ray detecting element 2, the level becomes low in the near part, and the level becomes high in the distant part. In such a way, a photodetecting sensitivity difference in infrared rays due to the distance in a detection area can be reduced, and the number of persons can be measured exactly. |
