The image plane of an optical or imaging system normally receives not only the image forming radiation, but also stray light which can reduce image contrast. This unwanted radiation is referred to as veiling glare. The veiling glare of lens on its own can be considerably different from the veiling glare of a lens system and camera body combination. In the latter case, reflection of part of the image-forming radiation from the image sensor in combination with further reflections and scatter from the lens system and camera body contribute significantly to the veiling glare.
One method of measuring veiling glare is termed integral method. With the integral method, the target object is a small black area surrounded by an extended uniform source. The veiling glare index is specified as the ratio of the irradiance in the image of the black area to the irradiance in the image of the extended source. In general, the integral method is applicable to systems where the scene will normally be of roughly uniform radiance, for example a landscape imaged in overcast conditions or with the sun behind the camera or lens system.
Labsphere has extensive experience at engineering extended uniform sources that are specifically designed to meet the need of your lens system or camera veiling glare characterization.