studio lighting
Lighting ratios Light meters are often incorrectly called exposure meters. Exposure is only one part of its function. It can also be used for measuring lighting ratios. This is achieved by taking an incident reading of the light source from the subject. The meter is pointed at a specific light source to measure the amount of light falling on the subject. If there is more than one light source each light can be measured independently by ensuring only one light source is on at any one time. In this way the ratios between the light sources can be measured. Lighting ratios and their relationship to SBR and latitude are best demonstrated and understood at a practical level. Take, for example, a photographer using a capture medium known to have a latitude of five stops. To make use of this information the photographer would try to light the subject to within this range. A five stop latitude would allow a photographer to use a maximum lighting ratio of 32:1 (5 stops). This ratio would retain detail in the highlights and the shadows.
Example 1 In a darkened studio a person is lit with a single light source from the right-hand side at 90 degrees to the subject. An incident light meter reading is taken from the right-hand side of the person’s face directly towards the light source. The aperture is f45 at 1 second. An incident light meter reading is taken from the left-hand side of the person’s face directly towards the opposite side of the studio to where the light is placed. The aperture is f4 at a shutter speed of 1 second. This is a lighting ratio of 128:1 (7 stops). To reduce this ratio another light or a reflector (fill) is placed on the left-hand side of the subject. The fill is moved towards or away from the subject until an aperture reading no more than three stops lower in number than that from the main light source (f16) is obtained. This is now a lighting ratio of 8:1.
128:1
8:1
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