| 摘要 |
PURPOSE: To obtain a small-sized zoom lens system in which the variable power ratio of a zoom lens which consists, successively from an object side, of a first lens group having a positive focal length and a second lens groups having a negative focal length and executing variable magnification by changing the spacing between the first and second lens groups to a ratio is increased as large as about >=2.5 times and which has good performance. CONSTITUTION: The first lens group 11 consists, successively from an object side, of a 1a-th sub-group 11a and a 1b-th sub-group 11b. Both of the 1a-th sub-group 11a and 1b-th sub-group 11b have one element of negative lens and satisfy the condition equations (1) to (5): (1) 3.5<fL/f1 <5.0, (2) 1.77<N1a N, (3) 35<ν1a N<50, (4) 1.77<N1b N, (5) 35<ν1b N<50. In the equations, fL: the focal length of the entire system on the long focus side, f1 : the focal length of the first lens group, N1a N: the refractive index of the (d) rays of the negative lens in the 1a-th sub-group;ν1a N: the Abbe number of the negative lens in the 1a-th sub-group, N1b N: the refractive index of (d) rays of the negative lens in the 1b-th sub-group;ν1b N: the Abbe number of the negative lens in the 1b-th sub- group.
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