Contrast Viewing FiltersnBalancing lighting by eye is a matter of experience. Decisions can be made easier by the use of contrast viewing filters.nnThese are designed to handicap the eye, with its much wider range of apparent densities, to resemble the range of different types of film. Use the contrast viewers to judge the relative densities of highlights and shadows.nnThere are viewers for black-and-white film, as well as various densities of viewers for colour film. A darker viewer is used for slower-speed film, where you would tend to use brighter lighting.nnFaster films, which can be used in darker environments, would require a lighter viewer.nnThe Tiffen #1 viewer is for black-and-white imaging. The #2 viewer is for film speeds up to 100; the #3 is for faster films. They can also be used for video, with the #3 being better suited to lower light levels. The green #4 viewer is for process photography. The blue #5 is for blue-screen work, as well as for adjusting colour video monitors.