Bought this lens off this forum. Problem is part of the time it focuses perfectly and other times it is blurry. Loaned the lens to another person who had the same experience. Then read on Fred Miranda people's review of this lens, and several reported the same problem and returned the lens to Sigma. Problem: What is an address for Sigma? Can't find one on Google, etc.
I like the pictures this lens takes when they are clear--just want the problem solved. ( Please don't say "I told you so" or something because I didn't get a Canon.) 
Karen
