Optical EngineeringTwo-element lenses for military applications
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To meet today's demanding requirements for increased performance, reduced size, lower mass, and cost, simple lenses containing multiple aspheric surfaces are required. It is now common for the number of aspheric surfaces used in an infrared lens to exceed the actual number of lens elements. Multiple aspheric and diffractive surfaces provide additional degrees of freedom in the lens design. This is required to achieve increased levels of imaging performance demanded by reduced pitch detectors. Aspheric surfaces also enable a greater diversity of materials to be used such that athermal solutions can be realized without the need for additional lens elements. More recent advances in detector technology will demand multispectral operation, but the requirements for simple, inexpensive optics will remain. Innovative use of aspheric components can also create very simple multispectral optics to fulfil this emerging need. This paper will review the range of applications that can be satisfied using no more than two optical components, highlighting the specific benefits that aspheric and diffractive surfaces provide. Consideration will also be given to future developments where enhanced functionality can be achieved using computational imaging techniques. Examples will be given for several military applications including weapon sights, driver's vision enhancement and remote weapon stations.