Patent ID: 8873161

Claim:
A zoom lens comprising: a first lens group having a positive refractive power, a second lens group having a negative refractive power, an aperture stop, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power, which are disposed in order from an object side, wherein the first lens group consists of a negative lens and a positive lens having a convex surface at an object side, which are disposed in order from the object side; the second lens group has, in order from the object side, a negative lens, a negative lens and a positive lens; the positive lens of the first lens group has an aspheric surface; an interval between the first lens group and the second lens group is increased and an interval between the second lens group and the third lens group is decreased when changing a magnification of the zoom lens from a wide angle end to a telephoto end; the first lens group and the third lens group are moved from positions at the wide angle end toward positions, which are at object sides thereof, at the telephoto end, respectively; the following conditions are satisfied: 1.52<ndP<1.6 2 (1) 60.0<νdP<85.0 (2) where ndP is a refractive index of a material of the positive lens of the first lens group for a d line and νdP is a dispersion; a partial dispersion ratio Pg, F is defined by the following formula: Pg, F =( ng−nF )/( nF−nC ) where ng is a refractive index of a lens material for g line, nF is a refractive index of the lens material for F line, and nC is a refractive index of the lens material for C line; Pg, FP is a partial dispersion ratio for a lens material of the positive lens of the first lens group and Pg, FN is a partial dispersion ratio for a lens material of the negative lens of the first lens group; and the following condition is satisfied: 0.0 07<ΔPg, FP<0.050 (3) where ΔPg, FP is defined by the following formula: Δ Pg,FP=Pg,FP −(−0.001802 ×νdP+ 0.6483); the following condition is satisfied: |Δ Pg,FP−ΔPg,FN|< 0.025 (4) where ΔPg, FN is defined by the Δ Pg,FN=Pg,FN −(−0.001802× νdN+ 0.6483) where νdN is a dispersion of material of the negative lens of the first lens group; and wherein the following condition is satisfied: 4.0 <fap/fw< 8.0 (5) where fap is a focal length of the positive lens of the first lens group and fw is a focal length of the zoom lens at the wide angle end, wherein the following condition is satisfied: 5.0< f 1 /fw< 8.0 (6) where f1 is a focal length of the first lens group and fw is a focal length of the zoom lens at the wide angle end.