Patent ID: 7274518
Filing Date: 2007-09-25
Classification: G02B

Abstract:
1. An optical system comprising four lens elements with refractive power, from the object side to the image side: a first lens element with positive refractive power having a convex front surface and a concave rear surface, and at least one surface of the first lens element is aspheric; a second lens element with negative refractive power having a concave rear surface, and the front surface and the rear surface of the second lens element are aspheric; a third lens element with positive refractive power having a concave front surface and a convex rear surface, and the front surface and the rear surface of the third lens element are aspheric; a fourth lens element having a convex front surface and a concave rear surface, the front surface and the rear surface of the fourth lens element are aspheric, and at least one inflection point is formed on the rear surface of the fourth lens element; an aperture stop located between the object side of the optical system and the second lens element, for controlling the brightness of the optical system; wherein the radius of curvature of a front surface of the second lens element is R the focal length of the fourth lens element is f