Patent ID: 7848015

Claim:
A two-element objective lens for an infrared optical system, consisting of: a) a first lens element receiving incident radiation and having front and rear surfaces, b) a second lens element receiving incident radiation from the first lens element and having front and rear surfaces, the first and second lenses forming an image on a focal plane; and c) an aperture stop placed between the first and second lens elements; wherein at least three of said surfaces of the first and second elements comprise aspheric surfaces; the lens has an f-number of between 1.1 and 1.4; the lens has a maximum radial field of between 5 and 15 degrees; the lens has an effective focal length less than about 6 inches; and the first and second elements are made from one or more materials selected to pass radiation in a desired infrared band of the electromagnetic spectrum; and wherein the lens features diffraction-limited performance in which the value of the modulation transfer function approximately matches a diffraction limit of the lens.