Design of a Step-Zoom Dual Field-of-View IR Telescope

Dual field-view optical telescope are commonly employed in the scanning infra-red imaging systems [1]. The wide field-of-view or low-magnification mode is used for observing a large scene area and searching for possible targets of interest. The narrow field-of-view or high-magnification mode is then used to see a close-up or magnified view of the target and for final target recognition and identification. The basic Kaplerian telescope in the high-magnification mode usually consists of a front objective and a rear eye-piece or collimator. The wide field-of-view is usually provided by inserting some extra lenses in the telescope (by a rotate-in or clip-in mechanism) at an appropriate location. In the narrow field-of-view mode, the extra lenses have to be parked outside the active ray-bundle using some mechanical mechanism.