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Exposure Modes

Digital cameras usually provide several exposure modes for your photographing pleasure. Although most cameras do an excellent job when left on autopilot, you gain a great deal more technical control and opportunity for creative image making when you explore the other exposure modes. Although the modes vary, some are common to nearly every camera. Typically, these include a semiautomatic mode, where you make certain exposure choices while the camera handles the rest; a full manual mode; and possibly a selection of scene modes that are designed for specific situations. Before we consider what each of these exposure modes is and what they have to offer you, let's take a look at the basics of photographic exposure.

What Is Exposure?

Simply put, exposure is the moment when the light strikes the film or sensor and the image is recorded. Three factors combine to determine the correct exposure for a digital image: the amount of light in the scene that strikes the CCD or CMOS sensor, the length of time that the sensor is exposed to the light, and the sensitivity of the sensor. Aperture is measured in f-numbers, and each number (commonly referred to as a stop) represents a factor of two in the amount of light admitted. The importance of a good exposure cannot be overstated. If an image is overexposed, the highlights will be completely white, without any tonal information (Figure 6.15). If an image is grossly underexposed, the image will be dark and lack shadow detail (Figure 6.16). All three of us are well versed in Photoshop, and while it can rescue us from slight exposure mistakes, no amount of Photoshop magic can save a picture that is extremely over- or underexposed. Fortunately, camera light meters are very sophisticated instruments and do an excellent job of determining the settings for a proper exposure in most common photographic situations. However, by changing any of the three main settings, you can gain control over certain characteristics that can influence the look of the image. We examine how light meters see the world in great detail in the next chapter.


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