Patent ID: 7382526

Claim:
An optical system projecting onto an image plane an object that is disposed at infinity by an intermediate image, said optical system comprising: a front group and a relay optic, each including a plurality of lenses, said intermediate image disposed between said front group and said relay optic; said optical system being configured as the object lying at infinity with at least two switchable and/or zoomable fields of view, said fields of view being imaged into said image planet; said front group including at least three lenses successively disposed towards said image plane; a first one of said lenses comprising of Ge; at least a second of said lenses comprising of ZnSe; and at least a third of said lenses comprising of either MgF2, CaF2 or MgO, wherein the front group includes a fourth lens, said fourth lens being a meniscus lens disposed adjacent to said third lens and nearer to said image plane.