| 摘要 |
PROBLEM TO BE SOLVED: To improve quality of light spot in an optical pickup device in which light spots are projected respectively on data part of optical disk different in radial directions, and seven data of data parts are read out from reflective light of each of the light spots. SOLUTION: Supposing an image surface 70 (a surface which gives a best aberration, i.e., a minimum aberration) on the side of an optical disk 34 of an objective lens 30, the best aberration points 73M, E, F, G, H, I, J corresponding to optical spots M, E, F, G, H, I, J are found on the image surface 70. The degree of distance from a main point 71 to each of the best aberration points 73M, E, F, G, H, I, J in the direction of an optical axis 32 are expressed by d0-d3 as attached figures to (d). The objective lens 30 is submitted to focus control so that the distance (d) from the main point 71 to the optical disk 34 is d0>d>d3.
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