An Imaging System Exhibiting Wavelength-Dependent Resolution

When homogeneous isotropic particles, such as crushed optical glass, are immersed in a liquid which has, at a specified wavelength, the same index of refraction as the particles but a different dispersion, light at the specified wavelength is unaffected in passing through the mixture. On the other hand, light of other wavelengths is dispersed. A cell containing such a mixture of solid particles in an appropriate liquid constitutes a Christiansen filter (see Figure 1) .1_4 The wavelength dependent action of the filter can be used to construct a low-pass spatial filter with a wavelength dependent cut-off. In particular, with the proper glass particles and liquid, the filter acts as weakly diffusing ground glass for the blue and red images while not affecting the green images. 1885 1902 THE BELL SYSTEM TECHNICAL JOURNAL, JULY-AUGUST 19GJ> An optical device using a color-selective spatial low-pass filter of this type is desirable in order to realize a proposed single pickup-tube color camera. 5,0 In this camera, color separation is achieved by modulating the amplitude of the color signals onto different carrier frequencies. These carrier frequencies are in turn generated by striped filters that have different spatial frequencies for the different primary colors. It is necessary to reduce the spatial bandwidth of the composite color image in order to meet the resolution limitation of the camera tube. This bandwidth reduction can be used because the human eye does not readily discriminate between composite images composed of three high resolution primary color images, and a composite image composed of a high resolution green image and low resolution red and blue images.