For any application where the mutually exclusive demands of moderately wide field of view and high resolution occur, lenses having a variable image scale have an enormous advantage over fixed lenses. In the field of thermal infrared optics, where diffraction limits ultimate resolution, there is therefore an increasing requirement for continuous zoom telescopes. Until recently, however, such telescopes have been precluded due to their excessive length. A continuous zoom telescope has been designed that combines wide maximum field of view with high maximum angular resolution inside an overall size less than that of many conventional fixed-magnification infrared telescopes. This compact size has had to be achieved commensurate with reason-able manufacturing tolerances. The manufactured unit has justified the expectations of high performance.