Patent ID: 7787189

Claim:
An objective lens system, comprising, in sequence from an object side to an image side: a first lens group having a focal length F 1 , having a positive first lens assembly with a focal length F 1 a and a negative second lens assembly with a focal length F 1 b , and the first lens assembly being used for focusing; a second lens group being a system of magnification variation with a focal length F 2 ; a third lens group for compensation having a focal length F 3 , the third lens group providing an image point of the second lens group in a location within the focal length F 3 ; and a fourth lens group having a focal length F 4 ; wherein the first, second, third and fourth lens groups form a finite conjugative system of magnification variation, and the system as a whole has a negative focal length, wherein the focal length F 1 a of the first lens assembly and the focal length F 1 of the first lens group satisfy the following requirement: 0.8F 1 ≦F 1 a≦ 1.2F 1 , and wherein the focal lengths F 1 , F 2 of the first and second lens groups meet the requirement: 1.8F 1 ≦F 2 ≦2.2F 1 .