| 摘要 |
Apparatus for optically scanning an information plane of a disc-shaped optical record carrier having an underlying surface extending parallel to the information plane. A radiation source supplies a scanning beam, and an optical scanning unit has a lens system which focuses the scanning beam to a scanning spot on the information plane. The lens system has an optical axis, a first lens unit with a first lens having an entrance side (11) and an exit side (13), and a second lens unit with a second lens situated opposite the exit side of the first lens. The scanning unit also includes a drive motor for displacing the first lens along the optical axis and a rotation element for adjusting the position of the second lens with respect to the underlying surface of the record carrier. To inhibit spherical and/or comatic and astigmatism aberrations during scanning, the rotation element is rotatably driven and forms part of the second lens unit. It is journaled in a stationary element (17), and has a disc-shaped surface provided with a pattern of grooves therein. This results in increased air pressure in the gap between the underlying surface of the record carrier and the rotation element during scanning, thereby maintaining a correct gap spacing.
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