| 摘要 |
PURPOSE:To effectively prevent the generation of contamination due to dust on optical parts and the blur of an imagery spot by constituting a transparent window members of a specific transparent plate and an engaging member for engaging the transparent plate with the aperture part of a casing. CONSTITUTION:The transparent window members are provided on the aperture part provided on the casing 9 for extracting convergent luminous flux from an objective lens 5 to close the inside of the casing 9. The transparent window members are constituted of the transparent plate 12 and the engaging member 11 for engaging the plate 12 with the aperture part of the casing 9. The transpar ent plate 12 is a parallel plane included within the range of 1.4 to 1.9 refractive index and the error + or -DELTAt(mum) of the designed thickness satisfies the condition + or -DELTAt<=-550.NA +330 when the number of apertures of the objective lens 5 is NA. Consequently the contamination of the optical parts can be effectively prevented and an efficient pickup function can be attained. |
