Patent ID: 8169718
Filing Date: 2012-05-01
Classification: G02B

Abstract:
1. In a wide-angle zoom lens having four groups of lens pieces which are the leading or foremost 1st lens group of negative refractivity closest to an objective field, the succeeding 2nd lens group of positive refractivity, the third lens group of negative refractivity, and the trailing 4th lens group of positive refractivity arranged in this order to move each lens group to vary optical power, the 1st lens group includes a front subset of the lens pieces of negative refractive power and a rear subset of negative refractive power the latter one of which is displaced toward the objective field for focusing from an infinitely far object to a near view; and the front end lens piece closest to the objective field in the 1st lens group is shaped in negative meniscus lens that has its concave surface faced toward an imaging plane and has the opposite surfaces shaped aspherical; the front and rear subsets of the 1st lens group meeting requirements of a focal length as expressed in the following formula: where f1a is a focal length of the front subset of the lens pieces in the 1st lens group and f1b is the focal length of the rear subset in the 1st lens group.