Here is a great invention by Joergen Geerds, a hardware based platform for doing exposure bracketing. Just when I released a software approach targetted at Nikon cameras Joergen releases a hardware approach targetting Canon!
Actually I suspect that both ways will work with both Canon and Nikon, but that is untested. Where as I’m using USB and WIA and PTP to control the camera from Windows Joergen is using a microcontroller and a cable release to the camera which is in Bulb mode to do variable length exposures.
I wish I could make Bulb mode work, but the way WIA just sends “commands” like “take picture” I don’t see how I can get an open shutter command and a separate close shutter command at a later time.