| 摘要 |
PURPOSE:To keep a focal length of objective lens of a fiberscope as specified at very low temperature by providing a projection in the objective lens and providing a recessed groove in the casing material. CONSTITUTION:The casing material 8 having a recessed part 10 is warmed and expanded until fitting to an objective lens 11 having a projection or a convex ring 12 becomes possible, and the lens 11 is fitted. Accordingly, the visual observation can be made without causing coming off of the objective lens 11 by this structure even if the very low temperature and the normal temperature are repeated. |
