Patent ID: 8085480

Claim:
A zoom lens comprising: a first lens group having a positive refractive power, including a negative lens and a positive lens and having at least one aspherical surface; a second lens group having a negative refractive power; a third lens group having a positive refractive power; and a fourth lens group having a positive refractive power and including a single lens; wherein the first lens group, the second lens group, the third lens group, and the fourth lens group are sequentially arranged from an object side to an image surface side, wherein, during zooming from a wide angle position to a telephoto position, the first lens group is moved so that the first lens group at the telephoto position is closer to the object side than the first lens group at the wide angle position, the second lens group is moved, the third lens group is moved toward the object side from the image side, and the fourth lens group is moved so that the distance between the third lens group and the fourth lens group at the telephoto position is larger than the distance therebetween at the wide angle position, and wherein the at least one aspherical surface of the first lens group is formed such that the positive refractive power of the aspherical surface is reduced as the aspherical surface gets closer to its circumferential portion from the optical axis with respect to a spherical lens having a paraxial radius of curvature of the aspherical surface, and the zoom lens satisfies the following Equations: vdG 1 −p> 56.0 2.1<|β3 T/β 3 W|< 5.5, where vdG1−p is an Abbe's number of the positive lens of the first lens group, β3T is the magnification of the third lens group at the telephoto position and β3W is the magnification of the third lens group at the wide angle position.