| 摘要 |
PURPOSE:To perform automatic focusing of a lens for forming a light spot to be disposed in front of a semiconductor optical position detecting element or a lens to be used in common with said lens by making the former lens movable in the optical axis direction. CONSTITUTION:A lens L1 is supported by a supporting member 13, and is moved in the optical axis direction by the revolution of the output shaft 12a of a motor 12. The detecting electrode of a semiconductor optical position detecting element 10 provided behind said lens is connected to the 1st arithmetic circuit I, by which the signal Ep corresponding to the ratio b/a between an image side distance (b) and the distance (a) from the lens L1 to an object is operated and outputted. On the other hand, in the 2nd arithmetic circuit II, the actual position information (b) of the lens L1 is detected, and the signal Vp corresponding to the ratio b/a' to the object side distance a' determined by the focal length (f) of the lens L1 is operated and outputted. The signal (g) for the difference between the signals Ep and Vp is outputted from a driving circuit III, by which the motor 13 is driven in the direction where the differential signal (g) is made to zero. |
