DEVICE FOR SCANNING AN OPTICALLY READABLE RECORD CARRIER

摘要

A device is described for optically scanning an information layer (2') by means of a focused radiation beam (5). Radiation reflected from the information layer is made astigmatic by an oblique plane parallel plate (50) and subsequently detected by a detection system (51). An electronic circuit (26) derives a focus error signal, representing the distance between the focal point (7) of the radiation beam (5) and the information plane (2'), from the electrical detector signals by using the high-frequency components in the detector signals. The influence of stray light falling on the detection system (51) on the focus error signal is thereby reduced.