Modulation transfer function of very high resolution miniature cathode ray tubes

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.