| 摘要 |
PURPOSE:To simplify the adjustment of an image rotating prism in locating a track and a boundary line of a 4-segment photodetector in parallel, by providing the image rotating prism to a condenser lens system. CONSTITUTION:A prism in which reflecting light rotates twice incident light is inserted between a cylindrical lens 8 and the 4-segment element 9. Thus, the image of the track is produced in parallel with the boundary line of the 4-segment element 9, while the direction of a generating line of the cylindrical lens 8 is placed coincidently with the direction of the track or orthogonaly thereto. The prism is usable in any case and better to be placed between the condenser lens 7 and the cylindrical lens 8 from the standpoint of the arrangement of the optical system. In using a reflecting prism 14, when the generating line of the cylindrical lens 8 is in parallel with or orthogonal to the track and an angle theta between the ridge line of the reflecting plane and the generating line is a half of 45 deg., i.e., 22.5 deg., the light image irradiated from the prism forms an angle of 45 deg., and one of the boundary lines of the 4-segment photo detector is placed in parallel with the track, the same as the case of the arrangement of the cylindrical lens at 45 deg. to the track. A focus detecting signal is obtained through the combination (SA+SB)-(SC+SD) of the photodetector elements split into four, and track detecting signal is obtained through the combination of (SA+SB)-(SC+SD). |
