| 摘要 |
PURPOSE:To detect a focus error by a grazing incidence method with one light source by mirror-finishing a part of a lens-barrel inner wall, making it into a mirror and executing the equal grazing incidence method. CONSTITUTION:A light flux 2 emitted from alight source 3 is reflected through a beam splitter 4 and a lens (lens system) 5 by a disk 1, returns to the original light path, is reflected by the beam splitter 4 and made incident on a photo detector 6. At such a time, a part of the light flux 2 is reflected by a mirror 20, comes to be a light flux 10 having a virtual light source 7, is reflected by the disk 1, reflected through the lens 5 by the beam splitter 4 and made incident on two divided photo detectors 8a and 8b. Since the spot is shifted to the 8a side and the 8b side in accordance with a focus error, a focus error signal can be detected from the difference in the output of the 8a and the 8b. Thus, the focus error can be detected by the grazing incidence method with one light source. |
