| 摘要 |
PROBLEM TO BE SOLVED: To sufficiently fix a lens without any cracking by providing a screw end part, which is made to abut against a lens surface, with a means which forms a groove on the lens surface when a screw is rotated. SOLUTION: The end part 46 has a center recessed part 48 arranged along the axis of the screw 40 and demarcates an edge end 50 isolated from the center axis. The end edge 50 is preferably circular and relatively pointed. When the screw 40 is rotated so as to move toward a wall and clamp the lens, the edge end 50 pushes a small amount of lens material away to form an arch- shaped groove 52 on the lens surface. The groove 52 becomes circular after the screw makes one rotation on the axis and is demarcated between the deposit 54 of a material in an external ring shape and a swell of the material at the center part, i.e., a projection part 56. The stress applied to the lens surface by the screw 40 is distributed over the surface without being concentrated on a single point. Therefore, the lens can be clamped and fixed tightly without being cracked.
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