03 Exposure Bracketing
Exposure Bracketing tends to divide opinion among photographers. Purists argue that a photographer should be able to calculate the correct exposure. Others say that the photo is what matters and any tool to help you get it right is worth using.
Working out the correct exposure is a great idea, but not so easy to achieve when you only have your camera’s internal light meter to rely on. We’ve already shown there are many technical shortcomings with even the most sophisticated metering systems.
Bracketing is a reliable fail-safe, then, for situations where you don’t have time to work out the perfect exposure or you have to make sure you get the shot. With film, it was a very wasteful technique, but with digital cameras there’s no such worry.
The principle of Exposure Bracketing is simple: the camera takes three shots at three different exposures: one correctly exposed, one under-exposed and one over-exposed. You pick the best and discard the other two.
You can set the degree of over- and under-exposure using the camera’s menus and controls. It’s hard to judge the best size for exposure increments; 0.7EV is a good starting point, while 1EV is better for high-contrast scenes where there’s more potential for error. Some cameras can take five bracketed shots as well as three.
On most DSLRs, the three shots are taken separately by default, so you have to press the shutter button three times. It’s easy to lose count and not complete a series, or inadvertently start a new one.
There is a better way. Set the camera to produce bracketed exposures as before, then set it to Continuous Shooting mode. Now, when you press and hold the shutter release, the camera will take all three bracketed shots in a row.
The only time when shooting bracketed shots individually is useful is when there are pedestrians walking in front of the camera, for example, and you have to wait for the right moment to take each shot.
Bracketing and HDR
There’s another reason to use Exposure Bracketing and it’s in the field of high dynamic range photography. This is a technique for photographing subjects with a much higher dynamic (brightness) range than the camera can record in a single shot.
Here, the bracketing steps are much greater – typically 2EV – in order to ensure that the full range of tones, from deepest shadows to brightest highlights, is recorded. Then the bracketed exposures are combined in software to produce a single high dynamic range image.
Photoshop’s HDR mode is designed specifically for this and there are third-party programs such as Photomatix that are even better. It’s a complicated and time-consuming process, but the results can be spectacular.
For this bracketing/merging technique to work, the images must line up as closely as possible, so using a tripod is essential.