Patent ID: 6778331
Filing Date: 2004-08-17
Classification: G02B

Abstract:
A zoom lens system comprising a positive first lens group, a negative second lens group, and a positive third lens group, in this order from an object,wherein upon zooming from the short focal length extremity to the long focal length extremity, all of said positive first lens group, said negative second lens group and said positive third lens group are moved; wherein the distance between said positive first lens group and said negative second lens group increases, the distance between said negative second lens group and said positive third lens group decreases; wherein each of said positive first lens group, said negative second and said positive third lens group is positioned closest to the object at the long focal length extremity; wherein said positive third lens group comprises a positive first sub-lens group and a negative second sub-lens group, in this order from the object; wherein said positive first sub-lens group is positioned at an object-side end of a reference distance which is defined as the longest distance formed between lens elements of said positive third lens group at the short focal length extremity, and said negative second sub-lens group is positioned at an image-side end of said reference distance; wherein said positive first sub-lens group is provided with at least one aspherical surface; and wherein said zoom lens system satisfies the following conditions: 1.73<2.5 âˆ’0.53bâˆ’4520 wherein fw designates the focal length of the entire zoom lens system at the short focal length extremity; f3 designates the focal length of said third lens group at the short focal length extremity; f3b designates the focal length of said second sub-lens group at the short focal length extremity; and &Dgr;Iasp designates the aberration coefficients of the aspherical-surface terms with respect to the third-order spherical-aberration coefficients of the aspherical surface under the condition that the focal length of the entire lens system at the short focal length extremity is converted to 1.0.