| 摘要 |
PURPOSE:To contain completely an objective lens in a cover, and to prevent the lens from being damaged and contaminated, by providing the cover between the objective lens and a disk, and making a hole of the cover smaller than the outside diameter of the objective lens. CONSTITUTION:A cover 12 is installed between an objective lens 1 and a disk 13, and a size of a hole provided on the cover 12 is made smaller than the outside diameter of the objective lens 1, and set to the minimum diameter which does not shut off an optical beam. In such a case, even in the upper limit position of the lens 1, a gap exists between the cover 12 and the lens 1, and even in the lower limit position, a gap exists between the cover 12 and the disk 13, therefore, each member is not brought into contact with each other. Accordingly, since the lens 1 is contained completely in the cover 12, generation of a damage and a contamination of the lens 1 can be prevented effectively. |
