Veiling glare measurements in the F4111 image intensifier

Veiling glare is a phenomenon present in most imaging devices and systems. It is a source of concern in proximity-focused image intensifiers where it causes a loss in image contrast, especially at low spatial frequencies. Veiling glare was measured in two different ITT F4111 18-mm image intensifiers, one with a fiber optic input window and fiber optic 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 excitation method. Near-field veiling glare, a measure of stray light close to a high-contrast edge, and far-field veiling glare, a measure of more widely distributed stray light, were measured as fractions of the 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 intensifier, and near-field veiling glare of 0.38±0.01 and far-field veiling 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 preliminary investigation suggests that the characteristic length for near-field glare increases with increasing wavelength.