Movie Makers (Jan-Dec 1953)

40 Incident light meters indoors: 2 Indoor lighting, to be pleasing, should be kept within certain contrast limits. The incident light meter creates the control LEO J. HEFFERNAN, FACL IN our opening discussion of this series (see Incident Light Meters Indoors: 1, December, 1952) we examined primarily into the use of the incident-light type -of■meter as a simple exposure calculator. We found that it could i>e used to determine exposure on foreground and background objects independently. We found also that certain minor compensations from the exposure indicated should be made in the case of subjects varying markedly in tonal value from the average. These variations we spoke of as being in subject contrast range. In our present discussion we shall examine, as promised, the use of the incident light meter in determining and controlling another factor — lighting contrast range. This function of the incident meter is as important in its effect as it is simple in its execution. For, to gain the most pleasing results, lighting on the average amateur set should be kept within certain acceptable limits of contrast. To illustrate how these controls are effected, let us backtrack for a moment and review the average amateur lighting setup. This will consist generally of two main light sources placed in front of the subject — the key light, which occupies a position above and to one side of the camera, and the fill light, which is positioned near the camera but on the opposite side to the key light. Supplementary lights used are the background light, which illuminates walls and background objects, and the back light, which shines from behind the actors or foreground objects to provide modeling and separation. The key light usually is placed first because it is important to have this light shining on the scene from the most effective angle. It establishes the lighting key or mood; and once the position and strength of the key light have been determined, it is then possible to strike a balance between it and the other lighting units. It is this balance between the key and the fill light which Leo J. Heffernan, FACL CONTRAST CONTROL begins by reading intensity of key light (pictured), then the fill. Note shielding of meter with cupped hand. determines what we have called lighting contrast ratio. Specifically, by lighting contrast ratio we mean the comparison in actinic strength between the key light and the fill light. Such a relation is indicated by the familiar terms of 1 to 1, 2 to 1, 3 to 1, etc. The ratio 1 to 1 would mean that the lights are of even strength; 2 to 1 indicates that the key light is twice as bright as the fill light, and 3 to 1 means that the key light is three times brighter than the fill light. For color work it is seldom that a greater lighting contrast than 4 to 1 is used, since the quality of the color suffers greatly when too little illumination is projected into the shadow areas. In black and white filming, far greater lighting contrast is permissible; and for dramatic effects a lighting contrast ratio of 16 to 1 is sometimes employed purposely. Determination of your lighting contrast ratio is a separate step in setting up the lights, which has nothing to do with determining the exposure to be given the film. Film exposure should be calculated after all lights are in position and are turned on. Furthermore, a cameraman should keep clear in his mind the difference between lighting contrast range and subject contrast range, discussed in December. The latter has to do with the reflectivity of various types of subjects. Our concern herein is with the comparative strengths of the key and fill lights. To measure these strengths the following steps should be followed: 1. With the other lights turned off, turn on the main or key light. 2. Hold the incident light meter at subject position, directing it toward the key light (see illustration). Note the light intensity reading in foot candles. 3. Turn off the key light and turn on the fill light; then direct the meter from the subject position toward the fill light. Note the light intensity in foot candles. 4. Divide the intensity of the key light by the intensity of the fill light and you will then have a known light balance or contrast ratio. If it is inconvenient to turn off the lights for individual readings, it is still possible to obtain a reading with both lights on by pointing the meter directly at the light being measured and shielding it with the cupped hand from the rays of the other lamps. This technique also is shown in the illustration. Let us suppose that you get a reading of 500 foot candles from the key light and 250 foot candles from the fill light. The key light reading (500) divided by the fill light reading (250) clearly equals 2, meaning that the lighting contrast is 2 to 1. Were the readings 500 and 125, the contrast would be 4 to 1 ; and if 500 and 500, then the contrast would be 1 to 1. To employ lighting contrast measurements to their full advantage, the cameraman decides ahead of time what degree of contrast he desires in a scene; he then measures the actinic values as he adjusts the lights to conform to his requirements. In determining what lighting contrast to use, the cameraman keeps [Continued on page 52]