| 摘要 |
PURPOSE:To perform an automatic focus control with no mechanical shift of a lens, by providing a transparent rotary disk having different thicknesses toward the revolving direction into an optical path and shifting the focus with said rotary disk. CONSTITUTION:A focus shift plate 72 constituting glass plates of different thicknesses and connected to a motor 71 is set into the optical paths of a total reflection mirror 107 and an image forming lens 108. When the plate 72 is turned, the focus shifts in response to the thickness of the plate 72. This plate 72 is a transparent disk which has different thicknesses, and the small center circle is split equally into two parts A (transparent) and B (opaque). A light emitting diode 74 is set at the position of parts A and B, and a phototransistor functioning as a photodetecting part 75 is provided opposite to the diode 74. The part 75 detects the light, and this light is amplified by an amplifier 76 to be used as a reference signal. |
