Bracketing is a technique used to take a series of images of the same scene at a variety of different exposures that "bracket" the metered exposure (or manual exposure). "Auto" simply means the camera will automatically take these exposures as a burst of 2, 3 or 5 frames with exposure settings of anything between 0.3 and 2.0 EV difference. This can be useful if you're not sure exactly how the shot will turn out or are worried that the scene has a dynamic range which is wider than the camera can capture. On a digital camera this can also be used to combine under- and overexposed images together to produce an image that could only have been taken if the camera had the same dynamic range as the scene, as shown in the example below. More about this in the tonal range topic.
When setting up for bracketing you can usually select the number of frames to be taken (typically 2, 3 or 5), the exposure setting and the order in which to take the shots (eg. 0,-,+ or -,0,+ etc.). It is important to note that the values are exposure compensation values.
The extreme example below was taken with auto bracketing of 5 frames at 1.0 EV in the -,0,+ order. Thus, in this case without bracketing the camera would simply have shot the frame with an aperture of f/4.0 and a shutterspeed of 1/160s. The +2.0 EV image was not used in the combination image.
|f/7.1, 1/306s, -2.0 EV||f/5.6, 1/224s, -1.0 EV||f/4.0, 1/160s, 0 EV|
|f/3.1, 1/71s, +1.0 EV||f/2.8, 1/39s, +2.0 EV||Combination of -2, -1, 0, +1 EV|
Some digital cameas also allow white balance auto bracketing.
This article is written by Vincent Bockaert,
author of The 123 of digital imaging Interactive Learning Suite
Click here to visit 123di.com