So, I've been toying with my Sigma f24 and just cannot get it to work with my 20D. It auto focuses, it snaps, but on shutter release registers an err99 and locks the camera. I've done some research and apparently it requires rechipping to support the newer protocol to communicate with the camera and vice-versa.
Imagine that...flashing your lens. One day it might happen but for now it looks like I'm in the market for a new wide angle/macro (not that what I had was anything to shake a stick at). Rechipping apparently runs 90-120 which for this low end lens is just a small bit below the actual retail price. Any body want a lens?
I think my next lens purchase will be the Canon EF 70-200mm f/4L USM. I can't afford the 2.8 version.