I mentioned in a previous thread that I'm looking into getting a Canon EOS-40D to go along with my 10D or replace it. I can get a new one from Amazon.com. Now I need an opinion on the Sigma 10-20mm. I'm looking at getting the Canon 10-22mm. However, to save some money I've also looked at the Sigma 10-20mm to save a couple hundred bucks. Any opinon on this lens?