| 摘要 |
PURPOSE: To make the effective diameter of a focusing lens group small and the moving amount for focusing small while maintaining excellent optical performance by specifying the constitution of the front group and the rear group of a first lens group. CONSTITUTION: This lens is provided with a first to a third lens groups G1-G3 of positive, negative and positive refractive powers, respectively, in order from the object side. The first lens group G1 has a front group G11 having a positive refractive power and a rear group G12 having almost the same positive refractive power as that of the front group G11 in order from the object side and, by representing the focal distance of the first lens G1 with f1, the focal distance of the second lens G2 with f2, the focal distance of the third lens G3 with f3, the focal distance of the front group G11 in the first lens G1 with f11, the focal distance of the rear group G12 in the first lens G1 with f12 and the focal distance of the whole lens system with F, the conditions shown by; 0.7<|f1.f3/(f2.F)|<1.3, 0.24<|f2|/f1<0.41, 0.7<f11/f12<1.4 are satisfied.
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