| 摘要 |
PROBLEM TO BE SOLVED: To reproduce a high-density disk and a standard density disk without changing the constitution of a device remarkably. SOLUTION: The central part of a light receiving element 8 is divided into a circular shape to form four sectorial shaped light receiving areas 85, 86, 87, 88 and peripheral light receiving areas 81, 82, 83, 84. At this time, the size of the circle shape is set to the size of area where the influence of spherical abberation in a reflected light from the standard density disk is small. When the optical characteristic of an objective lens detects a reproduced signal with respect to the standard density disk by using the light receiving areas, photoelectrically converted signals from the light receiving areas 85, 86, 87, 88 are used and at the time of detecting a focus signal, the signal is made to be calculated from the difference among photoelectrically converted signals from areas 81, 83, 85, 87 and areas 82, 84, 86, 88 facing to each other. |
