| 摘要 |
PURPOSE:To eliminate the flare to obtain images of good contrast by using a distributed index lens as a double convex position lens just before a stop of a stop postpositive lens and giving a negative gradient of refractive index to the apex of the image-side surface of the positive lens. CONSTITUTION:The first positive lens which has a convex surface having a high curvature on the object side, the second negative lens which has a concave surface having a high curvature on the image side, the third double convex lens 3, and the stop are arranged in order from the object side, and the third lens is constituted with a distributed index lens whose refractive index is varied in the direction of the optical axis. A gradient dN(x)/dx of the refractive index distribution in the direction of the optical axis at the apex of the image-side surface of the third lens in the case where the focal length of the whole of the system is standardized to one is set to satisfy a formula, thereby compensating aberrations.
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