Patent ID: 7929221
Filing Date: 2011-04-19
Classification: G02B

Abstract:
1. A wide-angle objective lens for receiving light from an object and for forming an image of the object on an image plane, the objective lens comprising sequentially from object to image of a first lens group, a second lens group and a third lens group, and: a) the first lens group comprising sequentially from object to image: a first lens element with a convex object surface and a concave image surface; and a first aspheric lens element having a concave image surface and a varying power that is negative at a vertex thereof and increasingly positive with radial distance from the vertex; b) the second lens group having a positive power; c) the third lens group having a positive power, wherein: two of the lens elements of the third lens group are joined to form a doublet; and one of the lens elements of the third lens group is a second aspheric lens element, d) wherein the lens elements are positioned to produce an image height, formed by a chief ray on the image plane, that is greater than the product of 1.2 times a paraxial effective focal length of the wide-angle objective lens and a field angle in radians of a corresponding object, and, e) wherein the total track length divided by the effective focal length of the wide-angle objective lens is greater than 15 and less than 25.