Just went to Cologne to check out some additional grads but found myself on a two day special sale! 30% of all Sigma glass! The result is I bought the Sigma 10-20mm 4-5.6! I came afternoon on the last day so I had no time to think. I own a 400D , canon 18-55 (kit), Sigma 70-300 and the canon nifty-fifty. This thing is going to be a king in my set! I am astonished with the HSM! I am kind of used to loud and slow lenses! Now , after buying it I checked out some reviews to find out all its' weaknesses, but all reviews say that there could be nothing bad for the price! Now really, what shouldn't I do with it? Also, how about filters? I heard pols give negative results? And Grads? My Cokin P holder will be visible on 10 mm? Then how do people make 10mm shots with a grad? Just hold it in front the lens? If I go for a slimline filter....77 diameter.... that's expensive! Thanks in advance!