Patent ID: 9063253
Filing Date: 2015-06-23
Classification: G02B

Abstract:
1. An imaging lens with an optical system comprising the foremost lens group closest to an object and of positive refractivity, the succeeding middle lens group, and the rearmost lens group closest to an image plane and of negative refractivity; the middle lens group, with the first, second, and third lens subgroups disposed in series, being moved axially along the optical axis for focusing; the foremost lens group having at least three or more convex lens pieces and a single concave lens piece; the imaging lens with the optical system meeting the requirements as defined in the following formulae: where Rn1 is a curvature of radius of a front surface of a concave lens piece the closest to the object of all in the foremost lens group, Rn2 is a curvature of radius of a rear surface of the concave lens piece the closest to the object of all in the foremost lens group, nd1 is the average of refractive indices of convex lens pieces in the foremost lens group relative to d-line, nd3 is a refractive index of the convex lens piece of the second lens subgroup in the middle lens group relative to d-line, vd1 is the average of Abbe numbers of the convex lens pieces in the foremost lens group, and vd3 is an Abbe number of the convex lens piece of the second lens subgroup in the middle lens group.