1. A infrared (IR) imaging device comprising: a focal plane array for detecting both MWIR and LWIR, said focal plane array having at least two pixels defining a pixel group, each said pixel having a pixel area, said pixel group having a pixel group area; optics for simultaneously directing said MWIR and said LWIR onto said focal plane array, said MWIR defining an M band, said LWIR radiation defining an L 1 and an L 2 band; an inhomogeneous filter overlaid on the focal plane array so that said M band passes through to all pixels, so that one of said pixels receives said L, band, and further so that the other of said pixels receives said L 2 band; and, said optics establishing an MWIR spot size and an LWIR spot size, said focal plane array being spaced-apart from said optics by a predetermined distance so that said MWIR spot size is about equal to said pixel area and said LWIR spot size is about equal to said pixel group area.