| 摘要 |
An apparatus is described for reading a record carrier with an optical information structure, which apparatus comprises an astigmatic focussing error detection system, said detection system comprising an astigmatic element and a radiation-sensi-tive detector which comprises four sub-detectors. By arranging the dividing lines between the subdetectors parallel to and perpendicularly to the effective track direction respectively and at an angle of 45 with the astigmatic focal lines, it can be avoided that the focussing error signal is affected by a movement of the radiation spot formed on the record carrier in n direction transverse to the track direction. |
