| 摘要 |
PURPOSE:To detect the focus of an object even in dark circumstance by provid ing a light source, which illuminates the object whose focal length should be detected, in a device. CONSTITUTION:The position of a top part 12a of a mirror 12 coincides with the optical axis of a convex lens 11 to divide all of the luminous flux transmitted through the convex lens 11 into low. A spot light source 13 is arranged in a position of the focal length passing a right face 12c of the mirror 12 from the convex lens 11, and a spot photodetecting element 14 is arranged in a position of the focal length passing a left face 12c of the mirror 12 from the convex lens 11. Since the spot light source 13 which illuminates an object 15 whose focal length should be detected is incorporated in the device in this manner, the focus is detected even in dark circumstances. |
