Patent ID: 9086562
Filing Date: 2015-07-21
Classification: G02B

Abstract:
1. A zoom lens comprising: a first lens group having positive refractive power; a second lens group having negative refractive power; a third lens group having positive refractive power; and a fourth lens group having negative refractive power, and configured of a single negative lens or of a cemented lens configured of a positive lens and a negative lens that are arranged in recited order from object plane toward image plane and are attached to each other, the first to fourth lens groups being arranged in recited order from the object plane toward the image plane, wherein a magnification-varying operation from wide end to telephoto end causes both the first lens group and the third lens group to travel toward the object plane and causes both the second lens group and the fourth lens group to travel along an optical axis, a focusing operation causes the fourth lens group to travel along the optical axis, and wherein the following first conditional expression is satisfied, where R4f is a radius of curvature of a most-object-sided optical surface in the fourth lens group, R4r is a radius of curvature of a most-image-sided optical surface in the fourth lens group, A is a number selected from the expression 0.7≦A≦1.0 and B is a number selected from the expression 3.5≦B≦5; wherein the following second conditional expression is satisfied, where fw is a focal length of whole of the zoom lens in a condition that infinite is in focus at the wide end, f4 is a focal length of the fourth lens group, M is a number selected from the expression −4.5≦M≦−3.5 and N is a number selected from the expression −1.3≦N≦−0.5; and wherein the following third conditional expression is satisfied, where f1 is a focal length of the first lens group, X is a number selected from the expression 1.5≦X≦2.0 and Y is a number selected from the expression 5.5≦Y≦6.0.