Normally, the exposure for portraits should be based on the fill light alone as measured at the subject position. The fill light is the single source of illumination to the shadow areas and image detail in the shadow areas.

Table 7-1. Corrective Treatments

Table 7-1. Corrective Treatments Continued

Table 7-1. Corrective Treatments Continued

When the exposure is based on the illumination intensity of the main light, the indicated f/stop produces underexposed shadow areas of the negative. With black-and-white negative film, the underexposure to the shadow areas may not be enough to cause loss of shadow detail. This is because of the greater exposure latitude and film processing latitude of black-and-white film compared to color negative film. With color negative film, however, underexposure to the shadow areas may cause loss of shadow detail and a color shift in the shadow areas that is uncontrollable in printing. Remember, basing your portrait exposure on the fill light alone applies only when the lighting ratios are within about a 2:1 to 4:1 range. Beyond a 4:1 lighting ratio, you may have to calculate your exposure based on both the main and fill lights.