Design and Use of Interference Passband Filters with Wide-Angle Lenses for Multispectral Photography

Abstract

A new type of interference filter is described, which can readily be designed for any central wavelength (400-900 nm) and any passband width (50-350 nm). These filters provide sharper cutoffs and greater efficiency than conventional absorption filters, and the total transmittance in the passband is shown to be two or three times greater, resulting in shorter exposures and, for example, about a twofold increase in the spatial resolving power over early space multiband photography experiments. It is also shown that locating the filter on a suitable lens surface will considerably reduce the shift of the passband for wide-angle photographic systems. Specifically, the spectral transmittance variation with field angle for the 90 degrees Geocon IV, the 90 degrees Paxar, and the 125 degrees S-Pleogon was calculated with a wide passband interference filter located on the second or fourth surfaces of the lenses. It is noteworthy that, with the filter on the second surface of the Paxar, spectral transmittance changes with field angle were negligible, and the modulation due to polarization was about 1%.