Canon’s Auto Exposure Bracketing Explained

Canon has made serious improvements in the Auto Exposure Bracketing in the EOS 50D / 60D / 7D and 5D2 although they still lack the ability to take more than three bracketed exposures at a time. Today, only the much more expensive EOS 1D Series cameras allow for more than three bracketed exposures. In these newer EOS models, Canon has combined Auto Exposure Bracketing with Exposure Compensation in a way that should make photographers working with HDR (high dynamic range) techniques very happy.

As you can see in this image, photographers can now use this feature to easily shoot a series of bracketed exposures covering the histogram from -4 EV to +4 EV in increments as fine as 1/3rd stop. For my own architectural HDR work I generally use the following series of nine exposures to provide the maximum dynamic range. I can take four continuous bursts of three bracketed exposures (I generally delete the three duplicate exposures) in less than 10 seconds.

Many of the latest EOS models have a new “function” button that can be set to display the EC/AEB settings as shown above. Once the EC/AEB settings are displayed I take the first set of three bracketed exposures with the camera set on continuous burst (high) with EC set at +2 EV. The three bracketed exposures take less than 1 second.

I then change the exposure compensation to +1 EV using the Quick Control Dial, hit the set button and take the next set of 3 bracketed exposures. Again, this takes less than 1 second. I continue this process two more times at -1 EV and -2 EV and end up with 12 exposures taken in less than 10 seconds. Its not as automated as using a Nikon D3 or D300 but it works fine for me.

EC Value  |  AEB Amount
+2 EV  |  +/- 2 EV = +4 EV, +2 EV, 0 EV
+1 EV  |  +/- 2 EV = +3 EV, +1 EV, -1 EV
-2 EV  |  +/- 2 EV = -4 EV, -2 EV, 0 EV
-1 EV  |   +/- 2 EV = -3 EV, -1 Ev, +1 EV

Results
-4 EV, -3 EV, -2 Ev, -1 EV, 0 EV, +1 EV, +2 EV, +3 EV, +4 EV

Do I really need nine exposures for my HDR work? Probably not, but I’ve yet to find an architectural situation where nine exposures didn’t adequately cover the entire dynamic range,  so for me this technique works perfectly. Its one more reason why the newer EOS cameras are a welcome upgrade from the previous models.

My basic HDR setup is fairly standard.
1) Camera on tripod, lens with AF on, IS off.
2) Set the AF point to ONE point, not “auto”.
3) Focus on the subject and set the lens’ AF to off (manual focus)
4) Take the bracketed exposures.
5) Review the histograms to make sure the entire dynamic range is covered.
6) Process in Photomatix Pro.

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