Well if it's a sigma lens, it might be one that is incompatible with newer canon bodies (DSLRs) if this is the case and you're handy, you might want to try this hack: http://www.martinmelchior.be/2013/04/con...-of-old-sigma-lens-to-work.html It involves adding an additional microcontroller inside your lens. Tricky but not Impossible (I just did it myself). Cheers, Jack