| 摘要 |
PURPOSE:To provide a compact zoom lens system of high variable magnification ratios by adding a lens group for focusing of simple constitution of the image side of the zoom lens consisting of 3 groups, and satisfying specific conditions. CONSTITUTION:The 1st group I on the object side consists of a positive lens and a negative lens, the 2nd group II of two negative lenses and a positive lens, and the 3rd group III of two positive lenses and each one of negative and positive lenses. The lens group for focusing on the image side is constituted of at least one piece of positive lens, and these are so constituted as to satisfy conditional formulas 1, 2, 3 where the focal lengths of the above-mentioned 3 groups are defined as f1, f2, f3, and the focal length of the entire system at the long focal length end is defined as fL. Thereby, zooming is accomplished with the positive refracting power group of a relatively small diameter as the 1st group, and focusing is accomplished with the focusing lens on the image side, whereby the compact zoom lens system of high variable magnification ratio is obtained. |
