2-Frame Bracketing with the Canon EOS 1D and 1Ds Mark 3

The key to changing the position of the bracketed shot, when shooting 2-frame brackets.

For quite some time Nikon’s mid- and pro-level bodies have had a novel and somewhat useful option for bracketing, a 2-frame auto exposure bracket. With the introduction of the EOS 1D Mark 3 in the spring of 2007 Canon brought that feature to their EOS-1 series digital bodies (the 1Ds Mark 3 will do this as well).

The catch is, while 3, 5, and 7 frame brackets are symmetrical around the middle exposure, with an equal number of over and under exposures, a 2-frame bracket is not. Nikon got around this by having two bracketing modes, +2F and -2F. Canon, however, didn’t seem to think it was necessary to include such an obvious way to control which direction the 2-frame bracket would be biased.

By default a 2-frame bracket has a non-biased normal frame and a negatively-biased bracket frame. In fact reading the manual one wouldn’t be faulted for assuming that the Canon 2-frame bracket only works as a negative bias.

The most obvious workaround, is to dial in a stop of positive exposure compensation; and in many cases that works fine. However, doing so limits the range of your exposure latitude from +/- 3 stops to+2 to -3 stops. If you want to keep the same +/- 3 stops of of exposure compensation but bias the bracket positively you’re seemingly out of luck

The truth is, there’s a side affect to another custom function that’s not obviously documented.

The trick to getting a “0,+” 2-frame bracket is actually one custom function away, at Custom Function 1-5. Custom Function 1-5 sets the AEB brackets sequence, giving us three options; 0, -, +; -, 0, +; and +, 0, -. What isn’t clear is that if you set C.Fn 1-5 to 2 (+,0,-) the 2-frame bracket becomes a positive-biased bracket not a negative-biased one. Either of the other two options (“-,0,+” and “0, -, +”) result in negative biased bracket frames.

AEB exposures with oEV, -3Ev and +3Ev of exposure compensation for a 2-frame bracket when Custom Function 1-5, Bracketing Sequence, is set to 0 or 1. Note the arrow on the vertical meter for the -3EV frame, indicating another exposure exists outside of what can be displayed.

AEB exposures with 0Ev, -3Ev and +3Ev of exposure compensation for a 2-frame bracket when Custom Function 1-5, Bracketing Sequence, is set to 2. Note the arrow on the vertical meter for the +3 Ev frame, indicating that another exposure exists outside of what can be displayed

It would have been nice if Canon had mentioned this instead of leaving it up to be discovered.