| 摘要 |
A field curvature corrector is provided which has a positive power and a positive exact field curvature (EFC) value for at least one principal ray, where the EFC value is given by:EFC=- SIGMA (n'-n)c/nn'the summation being taken over the surfaces of the corrector, and for each of the surfaces, n is the index of refraction on the object side of the surface, n' is the index of refraction on the image side of the surface, and c is the curvature of the surface at the intersection of the surface with the principal ray, c being positive if the center of curvature is on the image side of the surface. By means of the corrector, the field curvature of a positive lens system can be corrected without the use of negative lens elements.
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