CHAPTER THREE: Controlling and Evaluating Exposure
Incident metering works better for product photography because, very often, you are dealing with more than one light source and need to get the exact exposure settings for each area a source is lighting. For example, if you are lighting a small product, you take a meter reading of the main light from the product, and then set the flash output according to the exposure that you have planned for your scene (that is, ISO 200 at f/8.0 for 1/125 second). Your second source is the background light. Most likely, the background light won’t hit the background at the same angle or be the same distance from the background as the key light is to the subject. Therefore, the background requires a separate meter reading to determine the correct flash output setting. Most often, you don’t want your secondary light to be the same exposure as your main light. For low-key shots, you meter the light, and then underexpose from the meter reading; for high-key shots, you do the opposite. Incident metering is also important in single-light situations to ensure that the subject is getting enough exposure at all angles. You can take readings of the shadow areas to make sure that they are getting enough light to hold detail and determine if a reflector is needed to add a little fill light. AN ALTERNATIVE TO INCIDENT METERING You can use your camera’s spot metering function and a gray card as an alternative to incident light metering. It’s an inexpensive but somewhat less precise method when using continuous lighting. You can place the gray card in the area you want to meter, record the camera’s meter readings, and then adjust the lights accordingly by moving them, or by using diffusion or a dimmer, if so equipped.
Using the Histogram One of the most important tools you have to evaluate exposure is the histogram. The easiest way to determine if you need to adjust the exposure is to preview your image. If it looks too dark, add exposure; if it’s too bright, subtract exposure. This, however, is not the most accurate method of determining how much exposure compensation to use. To accurately determine how much you need to adjust your exposure, look at the histogram. The histogram is a visual representation of the tonal values in your image. Think of it as a bar graph that charts the lights, darks, and mid-tones in your picture.
69