| 摘要 |
PURPOSE:To reduce the deterioration of aberration by adjusting the shape of a flange surrounding the effective diameter of a plastic lens and uniformizing the inflow/outflow to/from an effective diameter area. CONSTITUTION:A part 14a of a flange 14 is removed so that an outer peripheral edge 15 connected to the effective diameter area 13 of the plastic lens 7 is exposed to outside air. When water is infiltrated into the lens 7 under high humidity, equal quantity of water is also infiltrated into any incident position in a direction along the optical axis in the effective diameter areas 12, 13 and refractive indexes are uniformly changed in the areas 12, 13. When parallel beams 18 having a wave front 17 vertical to the optical axis 16 are made incident on the lens 7, the beams are converted on a point P0 on the optical axis 16. At that time, a wave front 19 does not include a wave front aberration and is expressed by a circular arc around the point P0. After water absorption, the refractive index of the lens is increased and the point P0 is arranged adjacently to the lens 17, but because of no disturbance on the wave front, the movement of the converging position can be effectively compensated.
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