Zoom optical system

摘要

Provided is a zoom optical system which includes, in order from an object, a first lens group having negative refractive power and other lens groups, and in which an interval between each lens group changes upon zooming, wherein the first lens group includes a first negative lens which is disposed closest to the object and has a diffractive optical element on an image side lens surface, and a positive lens disposed closer to the image than the first negative lens, and the glass material used for the positive lens satisfies the following conditions expressions: ν1p≦35 and Δ(θg, F)≧0.007, where ν1p denotes an Abbe number, based on the d-line, of the glass material used for the positive lens of the first lens group, and Δ(θg, F) denotes a deviation of the partial dispersion ratio of the glass material, which is used for the positive lens, from a standard line that connects a glass type A and a glass type B in a graph of which abscissa is an Abbe number νd based on the d-line, and the ordinate is the 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: Glass type A: νd=60.49, (θg, F)=0.5436; glass type B: νd=36.26, (θg, F)=0.5828.

主权项

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:
ν1p≦350.012>Δ(θg,F)≧0.007where 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:
Glass type A: νd=60.49,(θg,F)=0.5436 Glass type B: νd=36.26,(θg,F)=0.5828 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.