| 摘要 |
PURPOSE:To detect the position while avoiding the deterioration of a frequency characteristic to the movement of a lens by providing an optical reflecting member moved with a lens having an optical characteristic representing focusing to an incident light and possible for movement in a direction at right angles to the optical axis. CONSTITUTION:When the objective lens 17 is positioned at a center B, a boundary line between optical reflecting planes 32a, 32b of the optical reflecting member 32 is placed at the center of the luminous flux from a light source 33, its luminous flux is reflected equally to the left/right and an equal luminous flux is detected for photodetection sections 35a, 35b of a photodetector 35. When the objective lens 17 is shifted largely toward the left side A, much luminous flux from the light source 33 is reflected on a light reflecting plane 32a and much luminous amount is detected by the photodetector 35a. Further, when the objective lens 17 is shifted to the right C, the operation is converse as above. Thus, the position of the objective lens 17 is detected by taking a difference of the luminous flux detected by the photodetection sections 35a, 35b. |
