Patent ID: 8654451

Claim:
A variable magnification optical system consisting of: a first lens group having negative refractive power; and a second lens group having positive refractive power, which are in this order from an object side, and a distance in an optical axis direction between the first lens group and the second lens group being changed when magnification is changed, wherein the second lens group consists of a positive sixth lens, a negative seventh lens, a positive eighth lens, and a cemented lens composed of a negative ninth lens and a positive tenth lens cemented together, which are in this order from the object side, and wherein all of the three positive lenses, which are the sixth lens, the eighth lens and the tenth lens, are double-convex lenses, and wherein at least two of the three positive lenses in the second lens group satisfy the following formulas (5) and (6) when partial dispersion ratio θgF for g-line and F-line is defined as θgF=(Ng−NF)/(NF−NC), where Ng, Nd, NF and NC: refractive indices for g-line, d-line, F-line and C-line, respectively, and wherein the following formulas (7) through (9) are satisfied: 80.0 <νd (5); 0.530 <θgF (6); 60.0 <νd 7 +νd 9<85.0 (7); ν d 7 >νd 9 (8); and 2.0 <f 7 /f 9<4.5 (9), where νd: an Abbe number for d-line, νd7, f7: an Abbe number of the seventh lens for d-line and a focal length of the seventh lens, respectively, and νd9, f9: an Abbe number of the ninth lens for d-line and a focal length of the ninth lens, respectively.