| 摘要 |
PURPOSE: To reduce the cost for the polishing and assembling of a lens while holding the lens performance excellent by constituting plural lens surfaces to be plane and satisfying specific inequalities. CONSTITUTION: The object-side surfaces of a 1st lens L1 and a 4th lens L4 are made plane and the opposite surfaces of a 2nd lens L2 and a 3rd lens L3 are made parallel to each other, and conditions I-IV are met: (I) 0.75<|f1÷Bf/f<2>|<1.45, (II) Di <|R1|, (III)ν2 <45, and (IV) 0.15<|β|.
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