LENS UNIT, OPTICAL SYSTEM, RECORDING/PLAYBACK APPARATUS AND METHOD FOR RECORDING TO AND/OR REPRODUCING FROM A RECORDING MEDIUM

摘要

A lens unit, an optical system, a recording/playback apparatus and a method for recording to and/or reproducing from a recording medium to compensate for a spherical aberration and perform stable recording or reproduction of data in recording or reproducing data to or from a recording medium having a plurality of recording layers are disclosed. The lens unit includes a first lens for condensing light beams outputted from a light source to a recording medium, a second lens for increasing a numerical aperture of the first lens to form a near field, and a liquid crystal device for compensating for a spherical aberration included in the first lens and the second lens, thereby compensating for the spherical aberration.