| Film | Cameras | Lenses | Lighting Light MeteringTo help photographers determine the ideal exposure, and to help them avoid the problems associated with extremely high or extremely low exposure levels, manufacturers introduced photoelectric exposure meters in the 1930s. At first, these meters were independent, handheld devices; later they were incorporated into the camera itself, with a sensor measuring the light as it came through the lens. The final development was automatic exposure, in which the camera uses data from its built-in exposure meter to automatically adjust the shutter speed and lens aperture. All metering systems share one principle: They respond to the world as if it were a uniform shade of gray. This shade (called 18 percent gray for its ratio of reflection) represents the average amount of light reflected by an average outdoor subject. In most situations, basing the exposure on this average reading produces ideal results: the negative receives just the right amount of light. The meters built into modern cameras are called reflected light meters: They measure the amount of light reflected into the lens by the subject. (Another type, the incident-light meter, measures the light that is falling on the scene or subject.) Most of these devices are also called averaging meters because they read a broad angle of the scene; those that read a narrow angle are called spot meters. Averaging meters provide somewhat less accuracy than spot meters but are easier to use. Spot meters give very precise readings, but the photographer must know how to correctly interpret these readings. Newer, more sophisticated single-lens-reflex (SLR) cameras try to increase the accuracy of their automatic-exposure systems with what is called a multipattern metering system. This type of system measures the light coming through the lens from several different areas within the picture frame. It then compares the results to a computerized formula to determine the best overall exposure. Based on the data gathered, these meters try to guess the kind of picture-taking situation at hand and compensate for some problems, such as an overly bright sky. Despite all the advances in exposure technology, meter readings are not foolproof. For example, neither very dark nor very light skin tones reflect 18 percent of the light, so portrait photographers have to adjust their exposures to compensate. In backlit conditions, when a person is surrounded by a bright background, most meters will recommend too little exposure. Likewise, if the main subject is a snowman in a field of snow, automatic exposure systems will assume that the snow is an average shade of gray and underexpose it. Next: Development and Exposure |