Now that we have taken a look at exposure basics and exposure compensation a good next step is to review exposure bracketing. Exposure bracketing is a feature found on most cameras, but not all. For example, several Nikon entry DSLRs lack this feature*. However users of these models should read this article to see if this is a must-have feature on their next camera.
Exposure bracketing has been used in photography literally forever. Bracketing exposures is simply the practice of taking one exposure at the recommended setting (usually from a meter) and then one or more additional exposures above and / or below that setting.
The practice of exposure bracketing started as a way to get ‘insurance shots’ when shooting in difficult lighting situations. As cameras became more sophisticated and electronic, automatic exposure bracketing (AEB) came to be.
The program-type film cameras of the 1990’s brought some basic automation to the process. The AEB setting would capture three images: one matching the meter, one over the meter and one under the meter. The photographer could specify the range of the bracket, usually between 1/3 stop and 2 stops, over and under. Photographers that used transparency (slide) film frequently used exposure bracketing because transparency film is notoriously unforgiving of exposure errors.
Funny thing, today’s digital cameras have many of the same characteristics of slide film. Unlike color print film, digital cameras and transparency film have a very narrow range of acceptable exposure. A little too much over exposure and we lose detail in bright areas, a little too much under exposure and detailed dark areas go black.
One use of AEB allows the photographer to capture three quick shots, each at a different exposure value, and later choose the better exposed image as a keeper. In this case “better” refers to the image that offers the best recording of important details.
A range of exposure bracketed image files.
But what if we could take the best of all three bracketed exposures and combine them into one image? Thanks to digital imaging we can do just that. The process is known as image merge or High Dynamic Range (HDR) photography. Digital software such as Photoshop, Photoshop Elements and Photomatix make it easy to turn bracketed images into a composite.
Bracketed shots compiled with software into a single image.
We have one big caution for photographers new to using AEB on their cameras. Once set, most cameras will remain in AEB exposure mode until the mode manually turned off. Even after the camera has been powered down and left idle for a few days. Avoid nasty surprises; always check your camera’s LCD panels to confirm current settings!
Summary: Auto exposure bracketing is a handy tool when photographers are confronted with complicated scene lighting or lighting that covers a very broad range. Cameras that offer AEB will allow the photographer to set the range of the bracket, often from 1/3 stop up to 2 full stops of variance from the meter reading. By selecting AEB and capturing three exposures across several stops the photographer is able to select the image with better exposure after the fact. A relatively new use for bracketed exposures is in creating composite images using software to create an image with the best exposure values from each captured image.
Please Note: There can be a difference between shooting with the camera set to capture JPG vs. RAW images. Without digging into a lot of technical detail, about two stops more information is available in RAW mode vs. JPG. It is possible with appropriate software to create three bracketed shots from one RAW image file: on target, +1 stop, -1 stop. Though the software may permit a broader stop range to be extracted from the bracketed images, few cameras can provide image files that contain enough image information to make broader stop ranges practical.
*Nikon DSLRs without auto exposure bracketing – D40, D40x, D60, D3000, D3100