An imaging system exhibiting wavelength-dependent resolution

The Christiansen filter consists of particles of a transparent solid immersed in a suitable liquid such that the two materials have different dispersions but equal indexes of refraction at some specified wavelength. This paper analyzes such a filter as an optical device for providing wavelength-dependent resolution. We derive the modulation transfer function of this filter by using the Huygens-Fresnel diffraction principle. General agreement is obtained with experimental measurements made using monochromatic light. One proposed single-tube color camera system for picture telephone service requires the three primary color component images to have different resolutions. An optical filter illustrating the characteristics required by this application was designed using the formulas developed in this paper. Subjective evaluation of the experimental results obtained with this filter indicates no unforeseen degradation of the composite image of the primary color components.