| 摘要 |
PURPOSE: To provide a long back focal length while keeping high image forming performance by composing the lens of lens groups having negative, positive and positive refractive powers in order from the enlarging side and specifying the relation of its constitution, refractive index, etc. CONSTITUTION: In order from the enlarging side, a lens group having a negative refractive power L1, a lens group having a positive refractive power L2, a diaphragm and a lens group having a negative refractive power L3 and arranged. The lens group L1 is composed, in order from the enlarging side, of one negative lens or two lenses of a positive and negative lenses, the lens group L2 is composed of a combined lens of a bi-convex lens and a negative lens, the third lens group L3 is composed of three negative, positive and positive lenses and the following three conditional relations are satisfied: 0.75<|f1|/f<1.25, 0.19<D2-3 /f<0.37, 0.12<N2p -N2n <0.18, where, f: the focal distance of the whole system, f1 : the focal distance of the lens group L1 (f1 <0), D2-3 : the interval between the lens group L2 and the lens group L3, and N2p , N2n : the refractive indices of the positive lens and the negative lens of the lens group L2.
|
