| 摘要 |
PURPOSE:To shorten the focal length of a wide-angle size and to obtain a high magnification ratio by moving a lens group for focusing whose focal plane is held constant for zooming from subject distance to the closest object distance. CONSTITUTION:The foremost lens group 1 is moved in an optical-axis direction within a range from an infinite subject distance to some subject distance L to perform focusing. While the lens group 1 is held after the optical-axis movement for the focusing up to the subject distance L, other lens groups 2-4 are moved in the range from the subject distance L to the closest subject distance M together with a focusing lens group to perform focusing. Further, zooming from the subject distance L to the closest subject distance M is carried out by moving the focusing lens groups 2-4 so that the focal plane is held constant. |
