Patent ID: 8049968

Claim:
In an inner-focusing zoom lens comprising multiple groups of lens pieces, including a first lens group of positive refractivity on the object side within the zoom lens, a second lens group of negative refractivity, and at least three trailing lens groups having positive refractivity, as a whole, at both the wide angle end and the telephoto end, wherein: the trailing lens groups include a third lens group of positive refractivity, a fourth lens group of positive refractivity, and a fifth lens group of negative refractivity all arranged in this order from an object side to an image side, the fourth lens group includes two or more negative lens pieces, at least one of which is connected on its surface to another lens piece to form a composite lens so that the junction between two of them functions to diverge incident beams; and a sum of the refractivities of all the junctions of the composite lens can be expressed as Σφ=Σ|(N1−N2)/R| where N1 and N2 are refractivities that substances before and after the junction of the composite lens respectively have, R is a radius of curvature of the junction, ft is a focal length of the comprehensive lens optics of the zoom lens at the telephoto end, and φt=1/ft is the refractivity of the comprehensive lens optics at the telephoto end, the requirements as defined in the following formula are satisfied: 2<Σφ/φ t< 10 (1).