Patent ID: 9535240
Date: 2017-01-03
CPC Classifications: G02B

Claim:
1. A zoom optical system which includes, in order from an object, a first lens group having negative refractive power, which is moved upon zooming, a second lens group which is moved upon zooming, a third lens group which is moved upon zooming, and a fourth lens group which is moved upon zooming, the first lens group including: in order from the object, a first negative lens, a second negative lens and a positive lens, the first negative lens being a meniscus lens with a convex surface toward the object and having a diffractive optical element on an image side lens surface; the second negative lens being a bi-concave lens, the positive lens being a meniscus lens with a convex surface toward an object, and a glass material used for the positive lens satisfying the following conditional expressions: where ν1p denotes an Abbe number, based on the d-line, of the glass material, and Δ(θg, F) denotes a deviation of a partial dispersion ratio of the glass material from a standard line that connects a glass type A and a glass type B in a graph of which an abscissa is an Abbe number νd based on the d-line and ordinate is a partial dispersion ratio (θg, F)=(ng−nF)/(nF−nC), with the Abbe number νd and the partial dispersion ratio (θg, F) of the glass type A and the glass type B being as follows: where ng denotes refractive index with respect to the g-line, nF denotes refractive index with respect to the F-line, and nC denotes refractive index with respect to the C-line of the Fraunhofer lines.