Patent ID: 7489452

Claim:
A telephoto zoom lens system comprises a positive first lens group, a negative second lens group as a focusing lens group, a diaphragm, a positive 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, said positive first lens group, said positive third lens group and said positive fourth lens group move toward the object, and said negative second lens group moves toward the image so that 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, and the distance between said positive third lens group and said positive fourth lens group decreases; wherein said negative second lens group comprises a first 2 a sub-lens group comprising a biconcave negative lens element in which the image-side concave surface has a larger curvature, and a second 2 b sub-lens group comprising cemented lens elements having a biconcave negative lens element and a biconvex positive lens element, in this order from the object; wherein said telephoto zoom lens system satisfies the following conditions: 1.6 <f s /|f 2 |<2.1 0.45 <|f 2bn |/f 2bp <0.8 wherein f s designates the focal length of the entire the zoom lens system at the short focal length extremity; f 2 designates the focal length of said negative second lens group (f 2 <0); f 2bn designates the focal length of said biconcave negative lens element of said second sub-lens group (f 2bn <0); and f 2bp designates the focal length of said biconvex positive lens element of said second sub-lens group (f 2bn >0).