I have posted this also in the Canon lens forum. Post it also here, hoping to get even more help.Reading the reviews of the Sigma 10-20, it seems to be a good choice among ultrawide alternatives, more so considering the price/performance.According to messages of existing owners, most of them seem to be happy with it, but some had to exchange the lens several times before they got a good copy, due to quality control issues at Sigma.I have now ordered one for my 50D and when it comes, I have to find out if it is a good copy or not. It should be easy to detect anormalies like one edge darker than the others, but more difficult to see if the sharpness is up to the good copies.I would highly appreciate recommendations on how to test the lens when it arrives. Thank you for your help!Alfred

1. Take a bunch of photos at a range of settings. 2. Look at the photos. 3. If you're happy with the images, you have a copy that is good for you.Some will all types of complex techinical checks on a lens, looking for edge focus issues, etc., and not be happy with any lens, but if the lens gives results that you like, it doesn't matter what others think.The Canon 17-85 is a good example. Some think it is a very good lens, while others think it is junk. Is it the difference between good and bad copies or between expectations? I think it's mostly the latter. -- Jeff PetermanAny insults, implied anger, bad grammar and bad spelling, are entirely unintentionalal. Sorry. http://www.pbase.com/jeffp25 http://www.jeffp25.smugmug.com