| 摘要 |
PURPOSE:To constitute a lens which has satisfactorily compensated aberations of various kinds and has about 1.0 telephoto ratio and a very short overall length, by including a lens system with refractive index variably distributed in the direction of the optical axis in constituting elements of a front group having the converging function and a rear group having diverging function. CONSTITUTION:This lens system consists of four lens groups, namely, a positive meniscus lens whose convex is directed to the object side, a double concave lens, a lens having a positive refracting power, and a negative meniscus lens, and the converging system of the front group consists of the first - third lens groups, and the converging system of the rear group consists of the fourth lens group. The refracting power of lenses in the front group is weakened to suppress higher aberrations and the assembling error is reduced, and a distributed index lens is used as the fourth lens to enhance its diverging function. The out-axis beams are diverged by the last lens having a wide field angle to compensate the coma, and the negative astigmatism generated in the first - third lens groups is compensated with respect to the out-axis beams; thus obtaining the photographic lens having about 1.0 telephoto ratio and a very short overall length.
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