Patent ID: 6809880
Filing Date: 2004-10-26
Classification: G02B

Abstract:
A zoom lens system comprising a negative first lens group, a positive second lens group, a negative third lens group, and a positive fourth lens group, in this order from an object,wherein upon zooming from the short focal length extremity to the long focal length extremity, the distance between said negative first lens group and said positive second lens group decreases, the distance between said positive second lens group and said negative third lens group increases, and the distance between said negative third lens group and said positive fourth lens group decreases; wherein said negative first lens group comprises a negative meniscus lens element having the convex surface facing toward said object, a negative lens element, and a positive meniscus lens element having the convex surface facing toward said object, in this order from said object; wherein said negative third lens group comprises a positive lens element and a negative lens element that are either cemented to each other or separated from each other, in this order from said object; wherein said positive fourth lens group comprises a positive lens element and a negative lens element which are either cemented to each other or separated from each other, in thus order from said object; and wherein said zoom lens system satisfies the following conditions: 0.253/ft|<0.5 0.0734)/log(Z)<0.17 âˆ’0.17Lâˆ’1/ftwherein f3 designates the focal length of said negative third lens group; ft designates the focal length of the entire zoom lens system at the long focal length extremity; m34T designates the combined magnification of said negative third lens group and said positive fourth lens group at the long focal length extremity; m34W designates the combined magnification of said negative third lens group and said positive fourth lens group at the short focal length extremity; Z34=m34T/m34W; Z designates the zoom ratio ((focal length at the long focal length extremity)/(focal length at the short focal length extremity)) of the entire the zoom lens system; and rLâˆ’1 designates the radius of curvature of the object-side surface of said negative lens element of said positive fourth lens group.