| 摘要 |
PURPOSE:To obtain a soft focus lens which does not change the focus position and is advantageous, by constituting the lens group consisting of three lenses so that the center lens can be exchanged and the lens group may be the soft focus lens when the center lens is exchanged for a junction lens. CONSTITUTION:The soft focus lens consists of three lens groups A, B and C in order from the object side, and the stop is arranged just before lens C, and lens groups A and C are connected into one body. When refractive indexes before and after the junction face of the junction lens of lens group B, the curvature radius of the junction face and the stop radius for opening are denoted as nB, nB', rB and R respectively, expressions I and II are satisfied. Lens group B can be exchanged; and when single lens B-L is used as lens group B, a general photographic lens is obtained; and when junction lens B-2 is used, a soft focus lens is obtained. Further, this soft focus lens is so constituted that the focus position and the back focus may be hardly changed even if lens group B is exchanged. |
