Patent ID: 8331043

Claim:
A fixed focal length optical lens system, comprising; a lens group and a diaphragm, wherein: said diaphragm is located in front of said lens group, said lens group comprising three lenses, respectively the first, the second and the third lens, which are sequentially arranged as a “negative-positive-positive” separated focal power system, said first lens is a double concave negative lens, said second lens is a positive meniscus lens, and said third lens is a double convex positive lens, wherein a concave surface of said second lens faces towards said diaphragm and a convex surface of said second lens faces away form said diaphragm, and a focal length of the entire optical system is f, focal lengths of the first, the second and the third lens are respectively f 1 , f 2 , and f 3 , and the ratio between the focal length of each lens and the focal length f of the entire optical system satisfies the following requirement: −0.7 <f 1/ f<− 0.5 1.0 <f 2/ f< 1.3 0.8 <f 3/ f< 1.0, and the first lens has a greater thickness than the second and third lenses.