| 摘要 |
PROBLEM TO BE SOLVED: To provide an image forming lens which is bright and wide in field angle and can have various aberrations compensated by arranging a 1st lens group of positive, negative, negative, and positive four-element constitution and a 2nd lens group consisting of >=1 lenses in this order from an object side, and forming those lenses of >=2 glass materials which have a <=0.0055 difference in dispersion. SOLUTION: The 1st lens group formed by arraying a 1st positive lens L1 , a 2nd negative lens L2 , a 3rd negative lens L3 , and a 4th positive lens L4 in this order from the object side and the 2nd group consisting of three lenses L5 , L6 , and L7 are arrayed in this order from the object side; and respective inequalities of -0.2<F/F1<1.0, -0.1<F/F2<1.4, 0.8<F/fa<2.0, 0.5<|F/fb|<1.5, 1.6<|F/fc|<3.0, and 1.0<F/fd<2.5 are satisfied so that the difference in dispersion between materials forming the lenses L1 -L7 is <=0.0055.
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