Patent ID: 7031073

Claim:
A zoom lens comprising, from an object plane to its image plane, a first lens group, which has a negative refractive power; a second lens group, which has a positive refractive power; and a third lens group, which has a positive refractive power; wherein as the second lens group moves from the object plane toward the image plane, the third lens group and the first lens group move with the second lens group, making the focal length of the zoom lens vary from long to short, and the zoom lens satisfies the following conditions: y/Trw> 0.1 0.23 <y/epw< 0.28 y/fw> 0.74 0.6<( R 23+ R 24)/( R 23− R 24)<1.14 2.09 <T 11/ D 11<5.85 0.53 <f 11 /f 1<0.61 where y is the image plane height; Trw is the total length of the zoom lens at its short focal length; epw is the eye piece position of the zoom lens at its short focal length; fw is the equivalent focal length of the zoom lens at its short focal length; R 23 is the curvature radius of the surface of a lens in the second lens group that is closer to the object plane; R 24 is the curvature radius of the surface of the lens in the second lens group that is closer to the image plane; T 11 is the boundary thickness of a lens in the first lens group; D 11 is the central thickness of the lens in the first lens group; f 11 is the equivalent focal length of the lens in the first lens group; and f 1 is the equivalent focal length of the first lens group.