| 摘要 |
A large zoom ratio, four-group zoom lens formed of only four lens groups is disclosed, namely, a first lens group of positive refractive power, a second lens group of negative refractive power, and third and fourth lens groups of positive refractive power. The first lens group includes, in order from the object side, a first lens subgroup that is fixed during focusing and a second lens subgroup that moves during focusing. The first lens group includes, from the object side, a first lens element and positive second, third, fourth, and fifth lens elements. To suppress spherical aberration, on-axis chromatic aberration, and distortion, specified conditions are satisfied for the refractive index, Abbe number, and radii of curvature of the object side lens element, the size of the image on the image plane, and the difference in Abbe numbers of the object side lens element and the lens element adjacent it.
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