Patent ID: 8149518

Claim:
A zoom lens system, comprising, in order of from an object side to an image side: a first lens unit which does not move for zooming and has a positive refractive power; a second lens unit which moves for zooming and has a negative refractive power; a third lens unit which moves for zooming and has a positive refractive power; and a fourth lens unit which does not move for zooming, is provided for imaging, and has a positive refractive power, wherein: the third lens unit includes a positive lens and a negative lens; and the following conditions are satisfied: −2.0×10 −3 <(θ pa−θna )/(ν pa−νna )<−1.4×10 −3 ; 41 <νpa−νna< 53; and 2.9<SGa3<3.2, where νna and θna indicate an average of Abbe numbers and an average of partial dispersion ratios, respectively, of materials of the negative lenses included in the third lens unit in case where the third lens unit includes a plurality of negative lenses or an Abbe number and a partial dispersion ratio, respectively, of a material of the negative lens included in the third lens unit in case where the third lens unit includes one negative lens, νpa and θpa indicate an average Abbe number and an average partial dispersion ratio, respectively, of a material of the positive lens included in the third lens unit in case where the third lens unit includes a plurality of positive lenses or an Abbe number and a partial dispersion ratio, respectively, of a material of the positive lens included in the third lens unit in case where the third lens unit includes one positive lens, SGa3 indicates an average specific gravity of the multiple lenses included in the third lens unit, and partial dispersion ratio θ is represented by θ=(Ng−NF)/(NF−NC) where Ng, NF, and NC represent refractive indices with respect to g-line, F-line, and C-line, respectively.