Patent ID: 8279520

Claim:
An optical system having a system focal length comprising: a first lens group comprising a plurality of lenses located along an optical axis, the first lens group being configured to correct for an axial chromatic aberration, the first lens group comprising a first lens element disposed to receive optical radiation and having a negative power, a second lens element having a negative power and an aperture stop provided at a first surface of the second lens element closest to the first lens element, and a third lens element having positive power, wherein the first lens element and the third lens element comprise germanium and the second lens element comprises AMTIR-1; a second lens group comprising at least a fourth lens element having a positive power, the second lens group being disposed adjacent the first lens group and spaced apart from the first lens group by approximately ⅓ of said system focal length along said optical axis, the fourth lens element comprising zinc selenide; and a third lens group comprising a plurality of lenses, the third lens group being configured to correct for a lateral chromatic aberration, the third lens group being disposed adjacent the second lens group and spaced apart from the second lens group by at least ½ of said system focal length along said optical axis, the third lens group comprising a fifth lens element having a positive power, a sixth lens element having a negative power, and a seventh lens element having a negative power, wherein the fifth lens element and the seventh lens element comprise germanium and the sixth lens element comprises zinc selenide, wherein the first, second and third lens groups are selected and arranged to provide a wide field of view greater than approximately 20 degrees and an f-number of less than approximately F/2 in a wavelength range between approximately 8 μm and approximately 12 μm.