Method and apparatus for optically reproducing a rotatable record with a scanning light beam of changing size

摘要

A rotatable record carrier upon which reproducible information is recorded in the form of spaced apart pits in substantially concentric circular tracks on a surface of the carrier. The pits may represent frequency-modulated information signals, and the lengths of the pits are independent of the frequency of the information signals. A method and apparatus for reproducing information from this record carrier is disclosed, wherein a light beam is used to scan the tracks of the record medium, and the size of the scanning light beam is changed as a function of the radius of the track which then is being scanned so as to increase the size of the beam when a track of larger radius is scanned. This control over the size of the scanning beam establishes a constant relationship between the size of the beam and the length of the pits despite changes in the pit length due to the different radii of the tracks.