| 摘要 |
PURPOSE:To make the extent of extension with respect to the same object distance the same despite magnification changing by changing magnification by the movement of the 1st group lens on the optical axis and the change-over of the 2nd lens group to the other lens group of different refracting powers in a lens system consisting of 3-group lenses of positive, negative and positive successively from the object side. CONSTITUTION:In the lens system consisting of the positive 1st lens group 1, the negative 2nd lens group 2-1 and the positive 3rd lens group, the 2nd lens group 2-1 is substituted with the other lens system 2-2 of a different refracting power, and the 1st group lens system 1 is moved to the object side, whereby the focus is made longer. Focusing is accomplished by moving the 2nd lens group 2-1 or 2-2 on the optical axis. Thereby, the extent of extension with respect to the same object distance is made the same despite magnification changing. |
