Patent ID: 8223224
Filing Date: 2012-07-17
Classification: G02B

Abstract:
1. A zoom lens comprising, in order from the object side to the image side: a first unit having a positive refractive power that is not moved for zooming; a second unit having a negative refractive power that is moved during zooming; a third unit having a negative refractive power that is moved during zooming; and a fourth unit having a positive refractive power that is not moved for zooming, wherein the first unit includes, in order from the object side to the image side, a front side partial unit having a negative refractive power that is not moved for focusing, a movable partial unit having a positive refractive power that is moved for focusing, and a rear side partial unit having a positive refractive power that is not moved for focusing, the rear side partial unit includes a plurality of positive lenses and one or more negative lenses, and the following conditions are satisfied: where νn is the Abbe number of the material of the negative lens that has the smallest Abbe number among the one or more negative lenses, θn is the partial dispersion ratio of the material of the negative lens that has the smallest Abbe number among the one or more negative lenses, νpa is the average of the Abbe numbers ν of the materials of the plurality of positive lenses, and θpa is the average of the partial dispersion ratios θ of the materials of the plurality of positive lenses, and where the partial dispersion ratio θ is provided by and equation of: where Ng is a refractive index of g-line, NF is a refractive index of F-line, and NC is a refractive index of C-line.