| 摘要 |
PURPOSE:To form small-sized detector for the number of persons which has large optical gain by providing a mirror with a concave surface which has focal length much smaller than the distance to an objective plane as a reflecting surface in a radial direction of the circular scan of the mirror, and making the center position of the concave surface in the radial direction of the circular scan nearly coincident with the center of rotation of the mirror. CONSTITUTION:The reflecting surface in the radial direction of the circular scan of the mirror M used for a circular scanning optical system is the concave surface which has the focal length much smaller than the distance to the objective plane. An optical path viewed from the photodetection surface S of an infrared detecting element is reflected by the reflecting surface of the reflecting surface of the mirror M, converged once in front of the mirror M, and diverged again to spread in the radial direction of the circular scan, so that a very wide visual field is obtained. Further, the center position of the circular scan of the concave surface in the radial direction is nearly coincident with the center of rotation of the mirror M, so the scanning optical system is reduced in size greatly. |
