| 摘要 |
PROBLEM TO BE SOLVED: To provide a zoom lens of which a half-field angle at a wide angle end is 38 degrees or more and a magnification ratio is 6.5 times or more, which has a resolution corresponding to an imaging device having 10 million to 15 million pixels, attained with as few lenses as about 10 lenses. SOLUTION: The zoom lens includes four lens groups comprising, in the order from an object side to an image side: a first lens group having a positive refracting power; a second lens group having a negative refracting power; a third lens group having appositive refracting power; and a fourth lens group having a positive refracting power, in which an aperture stop is disposed between the second lens group and the third lens group. Upon changing magnifications from a wide-angle end to a telephoto end, an interval between the first lens group I and the second lens group II increases, an interval between the second lens group II and the third lens group III decreases, an interval between the third lens group III and the fourth lens group IV increases, and the first lens group I and the third lens group III are moved, such that the first lens group I and the third lens group III locate nearer to the object side at the telephoto end than at the wide-angle end. In the zoom lens, the third lens group has a positive lens made of an optical material which satisfies the following conditions (1) to (3). There are: (1) 1.52<nd<1.62; (2) 65.0<νd<75.0; and (3) 0.015<Pg,F-(-0.001802×νd+0.6483)<0.050; where nd represents a refractive index,νd represents an Abbe number, and Pg,F represents a partial dispersion ratio defined by (ng-nF)/(nF-nC), where ng, nF and nC represent refractive indexes for g-line, F-line and C-line, respectively. COPYRIGHT: (C)2011,JPO&INPIT
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