A lens system includes a first lens with negative refraction power, and a second lens with positive refraction power. The first lens includes a surface facing the image side having an optical portion. The lens system satisfies the formulas: (1) Y/Z 1.49, wherein Y is a distance between an end point of the optical portion and a center point of the optical portion along a direction perpendicular an optical axis, Z is a distance between the end point of the optical portion and the center point of the optical portion along the optical axis, F1 and F2 are the focal lengths of the first and second lenses, respectively, G1R1 and G2R2 respectively denote the radius of curvatures of a surface of the first lens facing the object side and another surface of the second lens facing the image side.