| 摘要 |
A tele-photographic lens of a small F-number comprising a positive first lens group, a negative second lens group, a negative third lens group and a positive fourth lens group. Focusing is carried out by moving the third lens group in the direction of the optical axis. Assuming that the compound focal length of the first, second and third lens groups is f(I, II, III), and the focal length of the whole system is fT, the lens satisfies the condition of 2 fT<f(I, II, III)<2.6 fT for correction of aberrations with the lens in a state of being focused on an object located at infinity.
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