| 摘要 |
PURPOSE:To satisfactorily correct a chromatic aberration and a tertiary aberration by a small number of lenses, by combining at least one piece each of lenses by which a refractive index of a medium is heterogeneous, especially, increases or decreases in an axially symmetric manner against an optical axis. CONSTITUTION:When (r), N00, and N10 denote a distance from an axis of a light beam 3, a refractive index on an optical axis, and refractive index distribution constant, respectively, a P lens 1 of N10<0 and an N lens 2 of N10>0 are combined by using a medium whose refractive index distribution becomes N(r)=N00+N10r<2>. Subsequently, N10 of 486.1nm, 587.6nm, and 656.3nm wavelength is denoted as N10F, N10d, and N10C, respectively, nu10=N10d/(N10F-N10C) denotes an Abbe number of a distribution constant, and Abbe numbers of the P lens 1 and the L lens 2 are denoted as nu10P and nu10N, respectively. In such a way, at the time of nu10P/nu10N>2, a primary chromatic aberration of an optical system can be corrected satisfactorily. Also, a correction of a tertiary monochromatic aberration can be performed by adjusting the distribution constant N10, and giving a curvature.
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