| 摘要 |
PURPOSE:To effectively compensate various aberrations by providing a distributed index negative lens which is a convex lens, but has negative power on the whole where negative power is required in terms of the power arrangement of a lens system. CONSTITUTION:This optical system consists of the 1st positive lens which has a large-curvature convex surface on an object side, the 2nd positive lens which has a large-curvature convex surface on the object side, and the 3rd negative lens which has a large-curvature concave surface on an image side. Further, the optical system has a front group which has positive refracting power and a rear group so that a large air gap is left between them. The rear group consists of the 5th negative lens and the 6th positive lens.In this case,the 5th negative lens is a convex lens, but has negative power on the whole because its medium has a refractive index distribution which increases in refractive index from the optical axis to the outer peripheral part at right angles to the optical axis. Thus, surface shapes and the distributed index lens are selected to reduce the spherical aberration, coma aberration, distortion, etc.
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