| 摘要 |
PROBLEM TO BE SOLVED: To obtain a zoom lens which has a wide field angle and high optical performance over the entire power variation range and also make the whole lens system small-sized by composing the zoom lens of four lens groups and specifying the refractive indices of the respective lens groups and movement conditions accompanying power variation. SOLUTION: The zoom lens has 1st to 4th negative, positive, negative, and positive lens groups L1 to L4 in order the object side and is varied in power by varying the intervals between the respective lens groups. The 1st group L1 has negative lenses L11 and L12 which are concave to the image plane side, a positive lens L13 which is convex to the object side, and an spherical surface which increases in positive refractive index from the center toward the periphery. Conditions D1W>D1T, D2W>D2T, D3W>D3T, 0.4<|f1|/fT<0.56, 1<f2/fW<1.35, and 1.65<SKW/fW<1.95 are met, where Di is the interval between (i)th and (i+1)th groups at the wide-angle end and telephoto end, fW and fT are the focal lengths of the whole system at the wide-angle end and telephoto end, and SKW is the back focus at the wide-angle end.
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