Here's another setting you'll probably use often as a correction to a shot you've already taken: cranking the ISO up or down.
In the film days, ISO (also known as ASA) was a measurement of the light sensitivity of a particular kind of film. You'd buy ISO 100 or 200 film for bright outdoor shoots, and 400 or 800 for low-light situations. But now that you're digital, you don't have to fuss with swapping film rolls in and out; you can change the ISO setting of your camera with the push of a couple of buttons.
Lower ISO settings always produce better photo quality. So the only reason you'd ever want to crank it higher is to prevent blur in low-light shots. See Chapter 5 for a complete discussion.
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