Originally posted by markkuk Go to Rec mode menu (camera icon) page 4, choose E-Dial Programming, choose M mode (on page 2), set Green Button function to Tv Shift. As an undocumented side effect of this setting bracketing in M mode changes only shutter speed. See pages 22 and 78 of
the manual.
Control of bracketing in M mode is a huge undocumented gem. If the lens has an aperture ring, the same may be accomplished by using that for setting the aperture. (Tv shift is the default when aperture ring is used.)
Another helpful setting is to set bracketing to burst with a single shutter push instead of manually shooting through the sequence. There is a very real risk of missing a shot for larger brackets when doing so manually (don't ask me how I know this
).
Menu --> C2 --> 9. One Push Bracketing ON
When bracketing in a burst, Av mode with manual ISO (noted in other comments) may also be a good option, though applying -3 stops EC might be in order.
Steve