Once upon a time—in the days when we shot film—bracketing was an insurance policy. It was a technique we learned from professional photographers, and they did it because it was their business to come back with the shot every time, no excuses. So when they faced tricky lighting conditions they'd bracket the shot; that is, they'd make two, three or more exposures below the meter reading and two, three or more above it. Most of the time they'd do it by varying the shutter speed to keep the f/stop and thus the depth of field (the zone of sharpness in front and behind the subject) constant. They could also bracket by using the camera's exposure compensation feature.

Lindsay Silverman, Nikon senior product manager, is quite succinct about his reasons for bracketing: "Once in a lifetime shots," he says. "A sunset in Venice, a graduation ceremony, a multiple flash setup down under the Brooklyn Bridge. I couldn't come back to shoot those and, with film, I couldn't see my results immediately as I now can with digital photography, so I couldn't fine tune my technique on the fly." So he'd use his best metering know-how and technique. Then, because of "the paranoia factor," he'd shoot a one-third stop exposure bracket.

Today, with digital, we see our results right away and make adjustments on the spot. Does the image look too light? Make a -1/3 exposure compensation adjustment and shoot the scene again.

These days, why bracket?

Several reasons, actually. First, because of time. Maybe the situation doesn't give us the luxury of checking our results. We've got to shoot quickly, so we set our Nikon D-SLR for auto bracketing and we've got the tricky lighting covered.

Second, for creative control. Simply, the "over" or "under" image might be the one that best captures the mood of the scene.

Third, because we can choose to bracket not only exposure, but white balance and flash. White balance bracketing changes the color temperature to effectively cool or warm a scene by adjusting its blue and/or amber tones. Flash bracketing will quickly  and automatically bracket the output of a Nikon Speedlight while maintaining the camera's settings; most importantly, the amount of ambient light reaching the camera's sensor remains constant.