Patent ID: 7791824

Claim:
A telephoto lens system comprising a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power, which are arranged sequentially from an object side, wherein the first lens group comprises three positive lenses and one negative lens, the second lens group comprises a doublet lens made up of a positive lens and a negative lens, and the third lens group comprises a doublet lens made up of a negative lens with a concave surface toward the object side and a positive lens, and a positive lens, which are arranged sequentially from the object side, the telephoto lens system satisfying 0.450 <f 3 /f< 0.630 where f denotes the focal length of the lens system when the lens system is focused on an object at an infinite distance, and f 3 denotes the focal length of the third lens group; wherein, when np denotes the refractive index of each of the three positive lenses of the first lens group, each of the three positive lenses comprises, without any overlap, one of three materials respectively satisfying 1.42<np<1.50, 1.55<np<1.65, and 1.70<np<1.85.