I've heard mixed reviews of the Sigma 10-20. The 12-24 doesn't take front end filters. Its annoying trying to buy a UWA as the best ones are the Canon EF-S 10-22 and the Tokina 12-24. My 10D doesn't take the 10-22 and the Tokina seems to be available from Hong kong only. I would prefer to buy it from Jessops and try it out. I could get the Sigma 10-20 from Jessops and try it first. Actually I couldn't, 2-4 week delivery time
