Anyone here have any experience with the Sigma 18-50mm F/2.8 EX DC Lens?? I'm look for a lens with roughly the same focal length, but not sure if I want to spend the big bucks for Canon glass. I currently shoot mainly on location portraits with some studio work. My current lens are 70-200 f/4L, 85 f/1.8, 50 f/1.8 and a little cheapo canon 35-135 f/3.5. I'm looking to add a "wider" lens that would serve as a general purpose lense but also could work when in the studio, which gets kinda cramped when shooting with my current lens. Btw, I currently shoot with a Canon 30D. Any and all suggestions are appreciated.