| 摘要 |
A wide-angle lens of fixed focal length formed of four lens groups of negative, positive, positive and positive refractive power, respectively, in order from the enlarging side is disclosed. The fourth lens group as well as one of the lens groups of among the first lens group, the second lens group and the third lens group are fixed in position. The other two lens groups of among the first lens group, the second lens group and the third lens group are moved during focusing, and specified conditions are satisfied in order to: (1) insure that the wide-angle lens is nearly telecentric on its reducing side, (2) maintain favorable correction of aberrations, (3) maintain a sufficiently large back focus for insertion of necessary components, and (4) enable the wide-angle lens to be compact. Preferably, the movement amount during a given focus adjustment of one of the two moveable lens groups is directly proportional to the movement amount of the other moveable lens group.
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