Marshall, C: Exposure Made Easy

Photographers must adjust their aperture, shutter speed, and ISO (collectively, exposure settings) to produce an image that is not too light (overexposed) or too dark (underexposed). With a proper exposure, there is a full range of tones from light to dark, detail in the highlights and shadows, and good image color. Exposure settings can also be used for creative effect -- using a fast shutter speed can freeze motion, while using a slow shutter speed can produce an artistic blur. A wide aperture (large lens opening) is used to limit the image area, from front to back, that appears sharp (this can make the subject stand out); a narrow aperture (small opening) is used to record everything the lens "sees" as tack-sharp. With judicious use of these controls and, in some cases, the introduction of flash to bring up the light levels, photographers have the tools needed to craft powerful portraits and capture the majesty of nature.