| 摘要 |
PROBLEM TO BE SOLVED: To obtain a zoom lens that has fewer lenses constituting the entire system, the shorter entire lens length, and higher performance in which various aberrations, including color aberrations are corrected satisfactorily. SOLUTION: The zoom lens includes, in order starting from the object side to the image side, a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power. When the zoom lens zooms, the lens groups move having different loci. In such a zoom lens, the second lens group is composed of a graded index lens that has a graded index in which the refractive index of a material varies from its optical axis to a vertical direction. The grade index lens satisfies the condition -1.85<ϕ2s/Φ2<1, whereϕ2s represents the refractive power of a thin, homogeneous lens made of a material having a refractive index of N00d, andΦ2 is the refractive index of the second lens group. COPYRIGHT: (C)2008,JPO&INPIT
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