Patent ID: 8018660
Filing Date: 2011-09-13
Classification: G02B

Abstract:
1. A zoom lens system comprising, in order from an object side to an image side: a first lens unit having a positive refractive power; a second lens unit having a negative refractive power; a third lens unit having a positive refractive power; and a fourth lens unit having a positive refractive power, wherein the third lens unit is stationary and the second and fourth lens units move along an optical axis during zooming, wherein the fourth lens unit moves along an optical axis during focusing, wherein the fourth lens unit consists of a cemented lens in which a positive lens element and a negative lens element are cemented together, and wherein the zoom lens system satisfies the following conditional expression: where R42 denotes a radius of curvature of a cemented surface of the cemented lens, and TD4 denotes a thickness of the fourth lens unit along the optical axis, nd4n denotes a refractive index of a material composing the negative lens element, νd4p denotes an Abbe number of a material composing the positive lens element, and νd4n denotes an Abbe number of a material composing the negative lens element.