Two-position IR zoom lens with low f-number and large format

摘要

Abstract: We describe the optical, mechanical and servo designs for a motorized, two-FOV (field of view) IR objective lens for use in the 8 - 12 $mu@m spectral band. The FOV is changed by moving lenses axially instead of the more traditional approach which is to add and remove lenses. The advantages of this approach include: simple mechanics, since a single mechanism can be used for both adjusting focus and changing FOV; only one lens group need be moved; no stow space is needed for removed lenses; and fewer total lenses are needed (four elements). The lens is used with a low-cost, uncooled focal plane array. This dictates relatively fast F-number, large image format (F/1.1, 7.8$DGR narrow FOV, 155-mm narrow-field focal length), and low cost. This combination of wide field and large collecting aperture pose a difficult optical design challenge. The lens meets a range of military environmental requirements including immersion in one meter of water. We describe how the requirements were met. We have fabricated and tested five lenses and we describe the assembly and testing process and present a summary of test results.!3