Modulation transfer function of very high resolution miniature cathode ray tubes

Abstract

A simple, reliable, and accurate method of obtaining modulation transfer function (MTF) data from cathode ray tubes (CRT's) has been developed. This method directly generates a tube's MTF independent of drive electronics by electrically, optically, and mechanically obtaining the modulus of the Fourier transform of the CRT's line-spread function. Data have been obtained from commercially available and recently developed prototype miniature CRT's. These tubes have nominal faceplate diameters of one inch and are encapsulated assemblies containing CRT, deflection yoke, and shield. Military applications include helmet-mounted displays and tank-commander and gunner sights requiring the display of high-quality thermal and low-light-level TV imagery. The most widely used miniature CRT exhibits a severe degradation in MTF when the brightness (screen current) is increased. A reduction of this degradation has been demonstrated for a recently developed prototype employing a laminar-flow electron gun. At 20 C/mm and 10 µA of screen current, the MTF values for these two types were 20 and 44 percent, respectively. Off-axis measurements reveal that some CRT's with lower center MTF than these two types have higher off-axis responses. Such performance can be attributed to better deflection-yoke selection and electron-optic design, which optimize performance over an area rather than at the center of the faceplate.