| 摘要 |
The present invention relates to an optical system for performing radial tracking on an optical record carrier (100). The optical system contains light dividing means, e.g. a grating, for separating a light beam into a main beam (52) for reading and/or recording information as readable effects on the carrier, and a plurality of auxiliary beams (52a, 52b) applicable for radial tracking. The carrier contains readable effects arranged in multiple tracks in one or more spiral (s), where the one or more spiral (s) are separated by one or more guard band(s) (5, 15) in that two guard bands enclose multiple tracks. The optical system is adapted to perform radial tracking from the reflected light of a first auxiliary beam (52a) being positioned in a first guard band (5, 15), and the optical system is further adapted to select the second auxiliary beam (52b) in order to change the track position of the main beam (52) by performing radial tracking from the reflected light of the second auxiliary beam (52b) being positioned in a second guard band.
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