Wide-angle lenses possess a characteristic that off-axis ray bundles tend to "de-cluster" in front of the first element of the lens system, which enables an array of bandpass filters to be mounted there. This allows subareas across a wide field to be imaged through different spectral bands simultaneously, and through a shared aperture (i.e., the system's aperture stop). Ronian calls this "Multiple-Field Multispectral" (MFMS) imaging. One of the advantages of this approach to spectral imaging is that there is minimal spectral shift of the bandpass through each filter, as the central ray within ray bundles from each field is at normal incidence to the filter. This also results in minimal astigmatism introduced by the filter. This book discusses the optical design of MFMS imaging systems and suggests practical applications. |
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