Patent ID: 7535652

Claim:
A zoom optical system comprising, in order from an object side: a lens unit A with negative refracting power, including one biconcave-shaped, negative lens component; a lens unit B with positive refracting power; a lens unit C with negative refracting power; and a lens unit D with positive refracting power, wherein when a magnification of the zoom optical system is changed, relative distances between individual lens units are varied and the zoom optical system satisfies the following condition: 0.2 ≦d CD /fw≦ 1.2 where d CD is spacing between the lens unit C and the lens unit D on an optical axis in infinite focusing at a wide-angle position and fw is a focal length of an entire system of the zoom optical system at the wide-angle position; wherein a distance along the optical axis between the lens unit A and the lens unit B is varied for a purpose of changing the magnification; wherein the negative lens component of the lens unit A is configured as a cemented lens component constructed of a positive lens L AP and a negative lens L AN ; and wherein θgFp and νdp of the positive lens L AP satisfy the following Conditions (a) and (b): θ gFp=αp×νdp+βp (where α p =−0.00163, 0.6400<β p< 0.9000) (a) 3<νdp<27 (b) where νdp is an Abbe's number, expressed by (nd−1)/(nF−nC), of the positive lens L AP , θgFp is a partial dispersion ratio, defined by (ng−nF)/(nF−nC), of the positive lens L AP , nd is a refractive index relative to the d line, nC is a refractive index relative to the C line, nF is a refractive index relative to the F line, and ng is a refractive index relative to the g line, so that a coordinate (νdp, θgFp) representing a property of the positive lens L AP is positioned, in an orthogonal coordinate system where a value of νdp, is an abscissa and a value of θgFp is an ordinate, within a range where a region defined between a straight line expressed by the equation in the Condition (a) with the lower limit value of βp and a straight line expressed by the equation in the Condition (a) with the upper limit value of βp and a region defined by the Condition (b) overlap.