| 摘要 |
PROBLEM TO BE SOLVED: To hold pickup performance constant even for a disk which is different in the thickness of its projection layer by determining the position where an objective droops by gravity so that the offset component of a focus error signal becomes equal. SOLUTION: The support position of the lens holder 3 at a gravitational drooping position X is so set that the distance from the objective 2 to the recording surface 1c of the disk 1 is A+αfor a 1st optical disk and A-αfor a 2nd optical disk, where, A is the focal length of the objective andαis length corresponding to a half of the thickness of the 1st and 2nd optical disk protection layers 1b. When focus control is performed, a DC offset which is equal in moving absolute quantity is generated in a stationary state and heating value due to the DC offset at the time of reproduction of both the disks becomes equal, so the variation quantity of aberrations of the objective can be made constant and the pickup performance can be held constant.
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