| 摘要 |
PURPOSE:To improve focus detecting accuracy by light-shielding light reflected on the outer circumferential part of the end face of the polariscope side of an objective lens on the circumference of the cylindrical hole of a light shielding member. CONSTITUTION:The light of the outer side of an effective diameter (d) of an objective lens 6 is reflected on the peripheral part of a glass face 6a of the objective lens 6 and the refelected light is light-shielded by the periphery of a cylindrical hole 12 of a light-shielding member 13 at converging on glass master disk from a semiconductor laser 1 through the objective lens 6. That is, the light incident on a quadripartite pin photodiode 11 as a noise component is light-shielded. Thus, focus detecting accuracy by the quadripartite pin photodiode 11 is improved and the focus distance of the objective lens 6 can be defined precisely by a lens actuator 7 based on the detecting signal of it. |
