A lens system includes a positive refractive power first lens, a negative refractive power third lens, and a negative refractive power second lens in that order from the object side of the lens system. Wherein the lens system satisfies the following conditions: (1) D/TTL>1.2; (2) 4.5>R1R/R1F>2.2; and (3) f/R1F>3, wherein, D is the diameter of a maximal image circle of the lens system on a image plane of the lens system, TTL is a distance from a surface of the first lens facing the object side of the lens system to the image plane, R1R is the radius of curvature of a surface of the first lens facing the image side of the lens system, R1F is the radius of curvature of the surface of the first lens facing the object side of the lens system, and f is a focal length of the lens system.