| 摘要 |
PROBLEM TO BE SOLVED: To provide an inner focus type telephotographic lens which is bright and whose curvature of field is restrained to be small. SOLUTION: This lens is equipped with three lens groups, that is, a positive I group, a negative II group and a positive III group from an object side. The I group is provided with, in order from the object side, a positive I-1 lens, a positive meniscus I-2 lens whose convex surface faces to the object side, a positive meniscus I-3 lens whose convex surface faces to the object side and a negative meniscus I-4 lens whose convex surface faces to the object side, and the III group is provided with a meniscus III-1 lens whose concave surface faces to the object side and a positive III-2 lens. At least two of the lenses having positive refractive power in the I group satisfy conditions 1.55<n1<1.75 and 61<u1 assuming that the refractive index of the lenses is n1 and the Abbe number thereof is u1, and satisfy conditions -10<f/rIII-1-1<-1.5 and 0.003<dIII-1 to III-2/f<0.25 assuming that the focal distance of the telephotographic lens is (f), a distance between the III-1 lens and the III-2 lens of the III group is dIII-1 to III-2, and the radius of curvature of the object side surface of the III-1 lens is rIII-1-1.
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