Patent ID: 8477429

Claim:
A zoom lens system comprising, in order 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 to the image side during zooming from a wide angle end to a telephoto end and has a negative refractive power; a third lens unit which moves on an optical axis during zooming; and a fourth lens unit which does not move during zooming and has a positive refractive power, wherein the fourth lens unit is constituted by a front lens subunit having a positive refractive power and a rear lens subunit having a positive refractive power with an air interval therebetween, which air interval being the largest within the fourth lens unit, wherein the front lens subunit and the rear lens subunit each have at least one positive lens and at least one negative lens, wherein the fourth lens unit satisfies the following conditions: 0.8<(ν fp/νfn )/(ν rp/νrn )<4.0; and 0.8<|{(θ fn−θfp )/(ν fp−νfn )}/{(θ rn−θrp )/(ν rp−νrn )}|, where νfp and θfp indicate an average value of Abbe number and an average value of partial dispersion ratios θgF of materials of positive lenses included in the front lens subunit, respectively, νfn and θfn indicate an average value of Abbe number and an average value of partial dispersion ratios θgF of materials of the negative lenses included in the front lens subunit, respectively, νrp and θrp indicate an average value of Abbe number and an average value of partial dispersion ratios θgF of materials of the positive lenses included in the rear lens subunit, respectively, νrn and θrn indicate an average value of Abbe number and an average value of partial dispersion ratios θgF of materials of the negative lenses included in the rear lens subunit, respectively, wherein the following condition is satisfied: 1.8 <fGNL/f 42<6.5, where fGNL represents a focal length of the lens GNL and f 42 represents a focal length of the rear lens subunit, wherein the rear lens subunit includes a lens GNL formed of a material having a characteristic satisfying: −2.100×10 −3 ×νd+ 0.693 <θgF ; and 0.555<θ gF< 0.900, where νd indicates an Abbe number of the material and θgF indicates a partial dispersion ratio, with respect to a g-line and an F-line, of the material, and wherein the Abbe number νd and the partial dispersion ratio θgF with respect to the g-line and the F-line satisfying: νd =( Nd− 1)/( NF−NC ); and θ gF =( Ng−NF )/( NF−NC ), where Ng, NF, Nd, and NC denote refractive indexes with respect to the g-line at 435.8 nm, the F-line 486.1 nm, a d-line 587.8 nm and a C-line 656.3 nm of the material, respectively.