Patent ID: 7218444

Claim:
An imaging device comprising a refractive imager lying in an optical path and comprising a first lens group that forms an intermediate image of a scene on the optical path, wherein the first lens group comprises a first-lens-group positive-power lens, and a first-lens-group negative-power lens; a second lens group that relays the intermediate image to a final image surface on the optical path, wherein the second lens group comprises a second-lens-group negative-power lens, and a second-lens-group positive-power lens; and a third lens group that may be selectively inserted into the optical path between the first lens group and the second lens group and selectively removed from the optical path, wherein the third lens group comprises a third-lens-group positive-power lens, and a third-lens-group negative-power lens, wherein a location of the final image surface along the optical path is unchanged when the third lens group is inserted into the optical path and when the third lens group is removed from the optical path.