| 摘要 |
A retrofocus lens system has a negative first, a positive second and a positive third lens group. The first lens group includes an aspheric first lens, a negative meniscus second and third lenses that are convex on the large conjugate side, and a negative meniscus fourth lens being convex on the small conjugate side. The second lens group includes a positive fifth lens and a sixth lens joined to the fifth lens. The third lens group includes a positive meniscus seventh lens being convex on the small conjugate side, a biconcave eighth lens, a positive ninth lens joined to the eighth lens, a biconvex tenth and eleventh lenses, and an aspheric twelfth lens. The system satisfies 0.8<f2/f3<1.5, 1.6<|f1|/f<2.4, |f4|/f>30, f5/f>6, where f is a focal distance of the system, f2 and f3 are respectively focal distances of the second and third lens groups, |f1| is an absolute value of a focal distance of the first lens group, |f4| is an absolute value of an axial focal distance of the first lens, and f5 is an axial focal distance of the twelfth lens.
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