| 摘要 |
PURPOSE:To shorten the overall length of a zoom lens and reduce its size by composing the zoom system of the 1st positive group, the 2nd negative group, and the 3rd negative group, and increasing the refracting power of the 2nd group which varies the focal length. CONSTITUTION:The 1st group 1 has positive refracting power and moves forth and back for focusing, the 2nd group 2 has negative refracting power and moves forth and back to vary the focal length, and the 3rd group 3 has negative refracting power. The 4th group 4 has positive refracting power, consists of a single lens, and converges divergent luminous flux projected from the zoom system consisting of the 1st- the 3rd groups. The 5th group 5 froms an image at the focal point. A condition 1 is for size reduction while a large zoom ratio of about 6 is maintained, and the 2nd group variable power lens 2 is made to have large negative power to shorten the movement distance and also increases the zoom ratio. In this case, f2 is the focal length of the 2nd group and fW is the wide focal length of the whole zoom system. |
