Patent ID: 8279538

Claim:
A lens system comprising, in order from an object side: a first lens group with positive refractive power; a second lens group with negative refractive power that moves during zooming; a third lens group with positive refractive power; and a fourth lens group with positive refractive power that moves during zooming and focusing adjustments, wherein the first lens group includes a lens with positive refractive power and an Abbe number vd 1 x that satisfies a following condition, the second lens group includes a lens with positive refractive power and an Abbe number vd 2 x and two lenses with negative refractive power and Abbe numbers vd 2 y and vd 2 z respectively, the Abbe numbers Vd 2 x , Vd 2 y and Vd 2 z satisfying following conditions, and the third lens group includes a plurality of lenses with positive refractive power, an average vd 3 a of the Abbe numbers of the plurality of lenses with positive refractive power satisfies a following condition, and a sum ndts of thermo-optical coefficients of the plurality of lenses with positive refractive power in a temperature range of 40° C. to 60° C. satisfies a following condition, vd 1 x> 80 vd 2 x, vd 2 y, vd 2 z< 23 77.5 <vd 3 a< 82.5 −12.8×10 −6 <ndts<− 2.4×10 −6 .