Patent ID: 6785058
Filing Date: 2004-08-31
Classification: G02B

Abstract:
A zoom lens system consisting of five lens elements which are divided into a positive first lens group and a negative second lens group, in this order from an object,wherein zooming is performed by moving each of said positive first lens group and said negative second lens group in an optical axis direction; wherein said positive first lens group consists of a positive first lens element having a convex surface facing toward said object, a negative second lens element, and a positive third lens element, in this order from said object; wherein said negative second lens group consists of a fourth lens element which is formed as a positive meniscus lens element having the concave surface facing toward said object, and a fifth lens element which is formed as a negative meniscus lens element having the concave surface facing toward said object, in this order from said object; and wherein said zoom lens system satisfies following conditions: 1.2<ft/f1>1.8 3.8<ft/f1G<4.2 1&lE;SF1<6 â€ƒwherein ft designates the focal length of the entire zoom lens system at the long focal length extremity; f1 designates the focal length of said positive first lens element; f1G designates the focal length of said positive first lens group, and SF1 designates the shape factor of said positive first lens element, defined as SF1=(r2+r1)/(r2âˆ’r1); r1 designates the radius of curvature of the first surface of said positive first lens element; and r2 designates the radius of curvature of the second surface of said positive first lens element.