Apparatus and methods for modifying existing forward looking infrared systems and for forming new forward looking infrared systems. Generally, the system comprises a Galilean afocal system (26) in combination with a reimaging afocal system (22). A reimaging afocal lens system (22) is formed with at least first and second lenses (40,42,44) and a plane (50) for forming an image therebetween. A thermal reference source (58) is positioned in the imaging plane (50) of the reimaging system (22). The method for modifying an existing forward looking infrared imaging system includes positioning the reimaging system (22) along the optical path of the system between the Galilian lens combination (26) and the scanning device (20). According to a method for forming a forward looking infrared system an imaging lens system (18) is arranged along an optical path in combination with a detector array to focus collimated radiation upon the detector array. The detector array subtends the field of view along a first direction. A reimaging afocal system (22) is incorporated along the optical path to provide collimated radiation to the imaging lens system (18) and a scanning device (20) is positioned between the reimaging afocal system and the imaging lens system to vary the field of view along a second direction in order to provide a two dimensional image. A galilean afocal lens system (26) is positioned to receive radiation from a scene and transmit the radiation to the reimaging afocal system (22).
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