Design of Mechanically and Optically Compensated Compact Infrared Zoom Munitions Lenses

Two design approaches have been taken in the design of a compact infrared zoom lens to operate in the 3 to 5 micron spectral band, with an aperture of f/4.5: an overall length of less than 150 mm, and a diameter of 75 mm. The zoom range is to be 4X, with focal lengths from 50 to 200 mm and angular field coverages from 5 to 20 degrees. The first approach is the design of an advanced Mechanically Compensated IR Zoom Lens. This design based on prior COI 4X zoom lenses offers the most direct engineering design solution. The second approach is the development of an Optically Compensated IR Zoom Lens. This design concept has the potential of many advantages since it has only one moving part, and offers a simpler and lighter lens construction with greater reliability. A detailed optical tolerance analysis will be carried out for both types, including the effects of all element thicknesses and separations; as well as thermal effects and manufacturability.