| 摘要 |
PURPOSE:To obtain a telephoto lens having a simple structure and a low cost, by satisfying the prescribed conditions for a lens system including a fixed positive lens group, a negative variable magnification lens group and a master lens group in that order from the front side. CONSTITUTION:A telephoto lens system includes a fixed front positive lens groupI, a variable mangification lens groupIIand a master lens group III in that order from the front side. The group II is shifted toward a subject by a prescribed distance in a state under which the infinite distance is focused with the 1st focal length L as shown in the diagram. Thus the 2nd focal length S shorter than L is obtained. The group III includes a focusing lens group III-2 which can be move toward the optical axis and performs the focusing to the closest distance by rolling out toward the subject from the position shown in the digram. This roll-out degree differs by the L and the S. As a result, a telephoto lens can double perfectly two telephoto lenses with a simple and compact structure. |
