| 摘要 |
PURPOSE:To obtain a simple internal focus type converter in a lens system of 3-group constitution consisting of a positive lens, and combinations of positive and negative lenses from an object side by satisfying prescribed conditions. CONSTITUTION:A titled converter is constituted of 3 lens groups of a positive lens L1 and combinations L2, L3 of positive and negative lenses from an object side. The combinations L2, L3 of positive and negative lenses are moved in one body as roughly a nonfocus optical system G of Galilean type with respect to the positive lens L1 for the purpose of focusing. The lens L1 is formed as an interchangeable lens having different focal lengths. Even when the G is moved with respect to the lens L1, the focal length of the lens system of the entire part and the distance from the L1 up to a front side focus are constant and from infinite objects up to near distance objects are focused on a film plane Film. Thus in the stage of focusing at a near distance with the internal focus type photographing lens, the lens having the same focal length is realized with the simple constitution. |
