| 摘要 |
PURPOSE: To obtain a large variable power ratio without increasing various aberrations even in image pickup of a subject existing at a close range. CONSTITUTION: This zoom lens is composed, successively from a subject side, four groups form of a first lens group 11 having a positive refracting power, a second lens group 12 having a negative refracting power, a third lens group 13 having a positive refracting power and a fourth lens group 14 having a positive refracting power. The first lens group 11 and the fourth lens group 14 are fixed. The variation is changed by relatively moving the second lens group 12 and the third lens group 13. The zoom lens is so constituted as to satisfy 100<f1 /fw <500, 2.5<|f2|/fw <3.5, 1<f4 /f3 <2 when the focal lengths of the lens groups 11, 12, 13, 14 are defined as f1 , f2 , f3 , f4 and the focal length at the wide angle end is defined as fw . The lens so constituted as to satisfy 1.7<Nd2 , 1.7<Nd3 when the refractive indices of the lens groups 12, 13 are defined as Nd2 , Ndd3 .
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