Mid-wave Infrared Dual-field-of-view Lenses with High Ratio for Third Generation Thermal Imager

A Dual-field-of-view (DFOV) lenses has been developed, which is for MWIR band with high ratio used by 3rd generation thermal imager. The lenses change the field of view by flipping in or out a group of optical elements. The lenses' ratio of DFOV is six, the focal length of narrow field is 240 millimeter, F-number is 4. As a result of smaller pixel size, the lenses have to provide high image quality. It is folded to get smaller volume. Because the detector contains cold stop and the lenses contains moveable group, narcissus is examined and minimized. Reference source is set at a suitable position to correct non-uniform of detector. Field stop is set at the first image surface to minimize stray light. The lenses improve thermal imager spatial resolution by micro-scanning which is realized by jiggling motion of the last element at two directions.