| 摘要 |
PURPOSE:To obtain a small-sized zoom lens of simple constitution by setting the focal length of a lens group, the focal length of the whole system at the wide-angle size zoom position, and the interval between principal points of the lens group at the wide-angle aide zoom position and telephoto end side zoom position. CONSTITUTION:The lens system consists of the 1st, the 2nd, and the 3rd lens groups successively from an object side; focal lengths of the 1st and the 3rd groups are f1 and f3 and the focal length of the whole system is fW. Further, the interval between principal points of the 1st and the 2nd lens groups at the wide-angle side zoom position is e12W and the interval between principal points of the 2nd and the 3rd lens groups at the telephoto-side zoom position is e23T. Those focal lengths and intervals between the principal points are so set that -0.3fW<f1<5fW, -2.5fW<f3<-0.5fW, e12W>-0.5fW, and e23T>-0.4fW. Consequently, the 1st and the 3rd lens groups are moved monotonously toward the object side and the 2nd lens is fixed, so that the mechanism is simplified and reduced in side.
|
