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 well 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 or indeed there are possibly some situations where you as the photographer believe the camera’s exposure reading is not quite what you are looking for in the shot.
To counter this problem most modern digital cameras have a facility called Auto bracketing.
So what is auto-bracketing?
Well its a modern derivative of an old technique that film photographers used, particularly when using color transparency film. Transparency or slide film has a notoriously limited exposure range, in other words if you mis calculated the exposure by more than half a stop, the image could be badly over or under exposed. To counter this professionals would bracket their exposure, shooting at the correct, metered exposure then in half stops under exposed and over exposed.
This technique allowed them to get very close to the correct, actual exposure. As technology developed, camera manufacturers began to incorporated this technique into their cameras providing an automated way of doing this.
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-Bracketing.
There are many reasons to use auto-bracketing, even given today's advanced metering systems. Shooting outdoors when there is a high contrast range, for example. Perhaps a street scene with deep dark shadows. Here your camera might expose the shadows so dark that it is impossible to see anything in them.
Bright skies are particularly prone to become over exposed leading to blown highlights, shooting a bracket may help find a better exposure. Another obvious 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.
What are the Typical Settings
As we have mentioned, todays camera have a wide range of adjustments for bracketing. Obviously to bracket you change the exposure by a set amount but most camera will now allow you to set the exposure amount to either 1/3, 1/2 2/3 or 1 full stop, the last two being useful for HDR and the first where 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 correct 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 to low to hand hold it may bracket 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.Some cameras will incorporate bracketing on the mode dal with the settings in the menu system. Turning the mode dial will also set the camera to shoot a burst sequence. This is defined by the number of images you set in the bracket.
On consumer level cameras auto bracketing is often found in the menu system, rather than having a button or dial to activate the bracketing
Auto-bracketing is an often under used yet incredibly powerful tool for getting the correct exposure for your images. Unlike the days of film, it costs nothing to use it, but 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.