| 摘要 |
<p>[PROBLEMS TO BE SOLVED] It is an object to carry out good recording or reproducing for three kinds or more of optical recording media, the optical systems for which are used under different conditions. [MEANS FOR SOLVING THE PROBLEMS] An optical head (38) is provided with a movable lens system (100) comprised of a convex lens (7), a concave lens (8) and a convex lens (9), so that the optical head can record or reproduce information for three or more kinds out of BD, HD, DVD and CD systems. The movement of the convex lens (7) and the concave lens (8) in the optical axis switches among three or more values with respect to a distance between the main surface of an objective lens (14) and the objective point of the objective lens (14) and a beam diameter at a position of the main surface and of an objective lens (14) in accordance with kinds of discs (15). This corrects spherical aberrations resulting from thickness differences of the discs (15) in accordance with kinds of the discs (15) and efficiently guides light into an effective aperture of the objective lens (14) to increase the light use efficiency.</p> |
