VEILING GLARE MEASUREMENTS IN THE F4111 IMAGE INTENSIFIER

Veiling glare is a phenomenon present in most imaging devices and syst ems. It is a source of concern in proximity-focused image intensifiers where it causes a loss in image contrast, especially at low spatial f requencies. Veiling glare was measured in two different ITT F4111 18-m m image intensifiers, one with a fiber optic input window and fiber op tic output window (FO/FO), and the other with a quartz input and fiber optic output window (Q/FO), by means of a half-field high-contrast ex citation method. Near-field veiling glare, a measure of stray light cl ose to a high-contrast edge, and far-field veiling glare, a measure of more widely distributed stray light, were measured as fractions of th e illumination level. Near-field veiling glare of 0.4 +/- 0.1 and far- field veiling glare of 0.08 +/- 0.02 were measured for the FO/FO inten sifier, and near-field veiling glare of 0.38 +/- 0.01 and far-field ve lling glare of 0.03 +/- 0.002 were measured for the Q/FO intensifier. The characteristic length, which is a measure of the extent of veiling glare from the edge, was 0.69 +/- 0.04 mm (near-field) and 1.8 +/- 0. 4 mm (far-field) for the FO/FO intensifier, and 1.19 +/- 0.03 mm (near -field) and 6 +/- 1 mm (far-field) for the Q/FO intensifier. A prelimi nary investigation suggests that the characteristic length for near-fi eld glare increases with increasing wavelength.