| 摘要 |
PURPOSE:To protect the surface of a convex lens from contamination and maintain steady reading and writing of information for a long time by a method wherein the ratio of a distance between a surrounding wall and an optical disc to a distance between the center of the convex lens surface and the optical disc is not larger than 0.5. CONSTITUTION:A surrounding wall which has an outer diameter smaller than the diameter DO of an objective lens 3 and is closer to an optical disc 1 than to the center of the surface of a convex lens is provided around the convex lens surface. The ratio of a distance (f-h) between the surrounding wall on the objective lens 3 and the optical disc 1 to a distance (f) between the center of the convex lens surface is not larger than 0.5. Even if the optical disc 1 is turned, air touching the convex lens surface in the surrounding wall is kept from being replaced by the surrounding wall. With this constitution, contamina tion on the convex lens surface can be substantially suppressed. |
