| 摘要 |
PURPOSE:To hold a stable focus condition by separating a light beam reflected from information recording media into plural pieces and calculating the output of the light detecting device installed in the forward direction from an image- forming point of the separated light beam. CONSTITUTION:As a method for detecting a focusing error, detection is executed by obtaining the difference between the light quantity of the first light detecting device 30 and the light quantity of the second detecting device 31. Namely, by obtaining (30a+30b)-(31a+31b), the signal goes to zero at the time of focusing, and when an objective lens 25 and recording media 26 are too close as compared with the time of focusing, the signal of the negative value is obtained, and when they are too far, the signal of the positive value is obtained. The signal is processed, the feedback is given to the position of the objective lens 25, and the objective lens 25 is shifted to the correct position and as the result, the focusing can be executed. |
