When you press the shutter button on your camera, a huge amount of information is processed to determine the correct exposure, color balance, and focus. For 95% of the shots you take, this information is translated into a beautifully exposed photo. However, as good as modern digital cameras are, there are still some situations where they struggle with the lighting conditions. Indeed, there are situations where you as the photographer believe the camera’s exposure reading is not what you are looking for in the shot.
To counter this problem, most modern digital cameras have a facility called auto exposure bracketing.
A three-stop bracket
So, what is auto exposure bracketing?
It’s a modern derivative of an old technique that film photographers used, particularly when using color transparency film. Transparency (slide) film has a notoriously limited exposure range. If you miscalculated the exposure by more than half a stop, the image could be badly over- or underexposed. To counter this, professionals would bracket their exposures, shooting at the “correct”, metered exposure, then in half stops underexposed and overexposed. This technique allowed them to get very close to the desired exposure.
As technology developed, camera manufacturers began to incorporate this technique into their cameras, providing an automated way of bracketing. Modern digital cameras have refined this technique to a point where top-end cameras have an incredible range of auto bracket functions.
Why would I use auto exposure bracketing?
There are many reasons to use auto bracketing. Shooting outdoors when there is a high contrast range is one use. For example, imagine a street scene with deep, dark shadows. Here, your camera might underexpose the shadows so much that it is impossible to see any detail in them. Bright skies are particularly prone to becoming overexposed, leading to blown highlights. Shooting a bracket may help find a better exposure.
Another example of where auto-bracketing may be useful is in shooting HDR or high dynamic range images, where you merge a series of shots to extend the highlight and shadow areas of your image.
Auto bracketing allowed me to create an HDR shot in this location
What are the typical settings?
To bracket for exposure, you change the exposure by a set amount between shots. Most cameras will now allow you to set the exposure amount to either 1/3, 1/2 or 1 full stop, the last two being useful for HDR and the first for when you are looking to fine-tune the exposure in tricky lighting conditions. Beyond this, you can also specify the number of shots—usually from 3 to 9 images—with the metered exposure being the middle shot of the range.
Depending on which exposure mode you are using, either the shutter speed or aperture will change. Using aperture priority, the camera will bracket the shutter speed and maintain the aperture. Using shutter priority will fix the shutter speed and change the aperture. In program mode, the camera will use either, depending on the lighting conditions. For example, if it calculates that the lowest shutter speed might be too low to handhold, it may bracket using aperture instead.
Where do I find auto bracketing on my camera?
On higher-end cameras, auto-bracketing will often be found using a dedicated button and dial combination. Usually, you hold down a button, and rotate one dial—for example, the aperture dial—to change the exposure stop difference i.e. from 1/3 to ½, and the shutter speed dial to change the shot range from 3 to 5 to 7 and so on. On consumer-level cameras, the more advanced settings are often found in the menu system, leaving just a single button to activate the bracketing.
Image via Flickr
Pro cameras often have a dedicated bracket button
One feature that works well with auto bracketing is the continuous mode on your camera. When you set either a low speed or high speed continuous mode as opposed to single shot mode, the camera will rapidly take the exposure bracket in quick succession before stopping. To shoot again, just press the shutter again. This can be particularly useful if shooting an HDR sequence without a tripod as it minimizes any movement of the camera position.
Auto-bracketing is an often-underused, yet incredibly powerful, tool for getting the correct exposure for your images. Unlike in the days of film, it costs nothing to use it. Not only can it make sure you nail the exposure, but by examining each of the images in a sequence, you can begin to understand the nuances of exposure itself.