VARIABLE POWER OPTICAL SYSTEM, IMAGING DEVICE, METHOD OF VARYING MAGNIFICATION OF VARIABLE POWER OPTICAL SYSTEM

摘要

A variable power optical system having a high ratio of magnification variation and excellent optical performance, an imaging device, and a method of varying the magnification of a variable power optical system. The variable power optical system has, in the mentioned order from the object side, a first lens group (G1) having negative refractive power, a second lens group (G2) having positive refractive power, a third lens group (G3) having negative refractive power, and a fourth lens group (G4) having positive refractive power. The variable power optical system also has an aperture stop (S) provided between the second lens group (G2) and the fourth lens group (G4). When the magnification is varied from a wide-angle end state (W) to a tele end state (T), each lens group moves such that the distance between the second lens group (G2) and the third lens group (G3) increases and the distance between the third lens group (G3) and the fourth lens group (G4) decreases, and such that the aperture stop (S) moves together with the third lens group (G3). The variable power optical system satisfies a predetermined conditional formula.