| 摘要 |
PROBLEM TO BE SOLVED: To provide a zoom lens of a low cost having a variable power ratio of about 3, an F number of about 1.8 and well compensated aberration and composed of only spherical lenses. SOLUTION: This zoom lens arranges, in order from the object side, a first lens group Gr1 having a positive refractive power, a second lens group Gr2 having a negative refractive power, a third lens group Gr3 having a positive refractive power and a fourth lens group Gr4 having a positive refractive power and power variation and focusing are performed by moving the second lens group Gr2 and the fourth lens group Gr4. All the first to the fourth lens groups Gr1-Gr4 are composed of spherical lenses and satisfy the following condition. Relation: 0.45<|f2|/(fw .f1 )<1/2> <0.7, where f2 : the focal distance of the second lens group, f.: the focal distance of the whole system at the wide-angle end of the zoom lens and f1 : the focal distance of the whole system at the telescopic end of the zoom lens.
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