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Do It Yourself: Bracketing
Fine-tune your exposures with smart bracketing. Here‚s how to do it.

By Arthur Bleich

Many digital cameras have an auto-bracketing feature that allows three images (sometimes more) to be shot in rapid succession, each at a different exposure. The first picture is taken at the exposure the camera‚s light meter determines to be correct, followed by one under-exposed and another over-exposed. You can usually preset the amount of exposure difference between shots and sometimes even choose a different order, for example, „under-correct-overš or „over-correct-under.š

Bracketing was a „mustš in the days of film because you couldn‚t see how your pictures turned out until they were developed and printedŲ if your exposure wasn‚t correct, that once-in-a-lifetime shot could be ruined. Photographers used to bracket manually, actually changing the aperture or shutter speed by hand. As cameras became more sophisticated, automatic bracketing was added.

Even with a digital camera, bracketing is a valuable tool because it‚s hard to check exposure accuracy on the itty-bitty display unless you‚re willing to interrupt the flow of shooting by bringing up a histogram Ųif your camera has that featureŲ which is a graphic display used to confirm correct exposure values. Light falling on the monitor or one that‚s been set brighter or dimmer for easier viewing can make it impossible to see subtle nuances. Only by viewing your picture in an imaging program would you be able to tell if you hit the exposure on the nose or not. If not, even Photoshop magic may not be enough to resurrect a poorly exposed photo, especially one with burned out highlights; you can‚t bring back what isn‚t there.

Bracketing records at least two extra frames for every picture you take, so learn to use it wisely. First, decide what increments of exposure change you want to use. Many cameras will allow you to select full stops, half stops, or third stops of differences between pictures. Pick full stops to begin with so you can easily see the results. Then, fine tune the range down to half or third stops.

Let‚s say you‚ve set your camera to Aperture Priority, selected f-4, and your camera picks 1/00 sec as its „correctš exposure. If one-stop bracketing is selected, the first exposure will be at 1/100 sec, the second at 1/200 sec (the equivalent of one stop under) and the third at 1/50 sec (equal to one stop over). If your camera were set to Shutter Priority at 1/00 sec, the f-stops would change: f-4, f-5.6, f-2.8. When set to Program, the camera will decide whether to change the aperture, shutter speed, or both. If any of the f-stops or shutter speeds are out of range, most cameras will give you a warning or just pick a different combination to assure that the images are bracketed correctly.

The best times to bracket are under extremely bright or low lighting conditions, though some photographers do it routinely even with good lighting. When shooting under bright lighting, your overexposed shot will usually be wastedŲ the highlights may be way too light and the picture unusable. In this situation use „smartš bracketingŲ shooting one shot at the camera‚s suggested exposure, then one underexposed, and a second one underexposed even more.

To use smart bracketing, simply select Exposure Compensation in your menu (or with a camera button if there is one) and set it to the underexposure side by a full stop, half-stop, or third stop. Let‚s say you select minus one, a full stop. Your camera‚s „correctš exposure will now be underexposed by one stop. So when you bracket, the bracketing sequence will remain the same (correct, under, and over) but your exposures will really be „under by one stop,š „under by two stops,š and „correct.š You‚ve now eliminated the usually „wastedš overexposed picture in the sequence and have begun to bend bracketing to your will.

Of course, you can also go the other way, by setting the Exposure Compensation to overexpose (the plus side), which would give you one picture overexposed, another „correctlyš exposed and a third overexposed even more. That would be a good way to go for overly-bright scenes, such as you find at the beach or in snow country, where your camera‚s light meter usually gets fooled by the extreme brightness and underexposes, making most pictures look too dark.

I don‚t recommend using full-stops for most „smartš bracketing situations because they might be too extreme. Once you understand the concept, set your increments to half stops when bracketing normally-lit scenes. You might want to try larger increments, though, when the light is very low or extremely brightŲ you‚ll have to experiment to find what works best for you under those circumstances.

Once you learn how to „smartš bracket by combining exposure compensation adjustments along with your camera‚s auto-bracketing feature, you‚ll begin to get perfectly exposed pictures and won‚t have to rely on your imaging program to bail you out.

ŲArthur Bleich

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