The Measurement of the Modulation Transfer Functions of Fluorescent Screens

Abstract

Publisher Summary From the measurements made on the modulation transfer function of image tubes it has been found that the precise method of screen deposition can lead to marked changes in the shape of the curve. The modulation transfer function has two primary uses. First, in many cases the contrast can only be determined for very small images from the modulation transfer function by the measurement of limiting resolution. The main interest may nevertheless lie in larger images because of some other limit set by a component in the system, for instance a video amplifier. Second, if all the components of a complex system are linear, then the overall modulation transfer function can be calculated by straightforward multiplication of the individual modulation transfer functions. This type of measurement can, therefore, give the system designer a complete analysis of a complex optical system. By placing a fine slit close to the screen and bombarding it with electrons, a promising technique for the direct assessment of screens is being developed. Provided that this can give sufficient accuracy, it will be used to study the effect of screen-making techniques on the shape of the modulation transfer function. The techniques that were used for predicting the final image quality in relatively simple systems are no longer reliable in the vastly more complicated systems now in use. By using the “optical transfer function” to describe the resolution performance of an optical system or its components, a more reliable and informative analysis ran be made. The optical transfer function can be understood by considering the image of a sinusoidal grating of 100% contrast produced by an optical system.