My camera body is the Canon 50D. I currently have a Canon 28-135 f/3.5-5.6 IS lens which I use as my main lens. I am looking into getting a wider-angle lens, and have narrowed it down to the following two: Sigma 17-70 f2.8-4.5 Canon 17-85 EF-S f/4-5.6 IS (yes, I know that there are different/better options possibly out there, but for price and what I need it for at this time, those are the two choices I've narrowed it down to. So I need help choosing between them.) What I do: I do mainly portraits at this time (family, baby, kids, seniors, boudoir, etc.). I prefer to work in natural light whenever possible, but sometimes use indoor studio lights when possible. I prefer NOT to use the flash if I can avoid it. I am just now getting into wedding work, so I need a lens that works for this, as well. Here's what I think so far: the Sigma is less expensive than the Canon, which is a plus. The main plus I see with the Sigma, though, is that it might be better in lower-light conditions, going to f2.8, where the Canon is at f/4. However, the Sigma stops at 70mm whereas the Canon goes to 85mm, which means I'll have to change lenses that much less with the Canon. The Canon also has the IS feature, whereas the Sigma does not. Help? I keep going in circles here.