| 摘要 |
PROBLEM TO BE SOLVED: To obtain a filter by which the deterioration of an image quality due to a ghost caused at the time of attaching the filter is reduced without largely impairing the optical performance of an image pickup lens. SOLUTION: An object side surface and an image side surface of a light transmitting member of the filter are made into a spherical shape, and the radius of curvature and the effective diameter of a light beam satisfy the conditions of: 0<|r1|-√(r12-(a/2)2)<=5 and 0.98<r2/r1<1.02. Then, r1 and r2 respectively mean the radius of curvature of the object side surface and the image side surface of the light transmitting member and (a) means the effective diameter of the light beam of the filter.
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