| 摘要 |
PURPOSE:To well compensate various aberrations, which are generated when the refracting power of each lens group is increased, and shorten the overall optical length by setting a distributed index lens having a prescribed shape in a lens system constituting a photographic lens. CONSTITUTION:At least one lens L of the photographic lens system is constituted to satisfy N>0 when the refractive index in the direction orthogonal to the optical axis of an internal medium of the lens L is N(h)=N0+N1h<2>+N2h<4>+ N3h<6>+N4H-u8+N5h<10>- where (h) is the height from the optical axis, and this lens system is constituted to satisfy conditions of inequalities (1) and (2) where (f), L, and D are the focal length and the overall optical length of the lens system and the lens thickness of the lens L respectively. If the overall optical length is longer than the upper limit of the formula (1), the effect of the use of the distributed index lens is reduced. If a partial charge of refracting power is reduced beyond the condition of the inequality (2), the curvature of field is increased, and it is difficult that a good optical capacity is obtained while shortening the overall optical length.
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