| 摘要 |
PURPOSE:To simplify the structure of a focusing device and to improve the reliability of the device by moving or rotating only an optical system to detect the focusing state. CONSTITUTION:A light beam emitted from a light emitting element 3 is projected into a subject 8 by a projection lens 1, the reflected light is bent by a plane mirror 21 through a photodetecting lens 3 and its image is formed on a two-divided photodetecting element. A photodetecting spot image is formed on a position separated from the dividing line of the photodetecting element 4, and when a fixed difference is generated between the quantity of light made incident upon two photodetecting surfaces, the difference of the quantity of light is detected by a photodetecting circuit and decided as a defocused state and the rotating direction of a focus ring 5 is detected. A driving circuit rotated the focus ring 5 and moves a optional system holding member 22 through a rink mechanism 7 in a direction that the center of the photodetecting spot coincides with the dividing line of the photodetecting element 4. When the dividing line of the photodetecting element 4 coincides with the center of the photodetecting spot and the difference of the quantity of light made incident upon the two photodetecting surfaces is reduced less than the fixed value, and decided, as the focusing state. Consequently, the reliability of the focusing device can be improved. |
