A system for generating custom variable neutral density filters has been built, characterized, and demonstrated. The desired densities for a neutral density filter are entered into the controlling computer as a function of distance. The program which generates the filter density profile is designed to vary the exposure time by controlling the velocity of the film as it moves under a slit aperture. A custom illumination system was designed and built to provide constant lamp output. The technique can provide the film with the exposure necessary to produce a given density profile
