Nikon 16-85mm f3.5-5.6g Sigma 17-50mm f2.8 EX DC OS HSM Nikon 17-55mm f2.8g ED-IF I recently bought the 16-85 but I find it slow and not sharp. The rest of the lens is fine but the actual optical performance strongly leads to desire so I'm looking into other options. The sigma 17-50 seems like a strong semi-fast and toted to be one of the sharpest standard zooms you can jam on your SLR and at a reasonable price. To add the 50mm at the long end is a bit shorter than I'd like but not a deal breaker. The dilemma is that I heard there are issues with its interaction with the Nikon D7100, which is the camera I own. I heard there are OS issues and other annoying issues. Nikon 17-55, a pro lens, but I am having an issue in seeing its value. It's apparently not all that sharp and it's very heavy--the same weight as my 70-300! I found someone willing to sell theirs for $700 CAD. Can someone better explain to me what makes this lens so special and a contender vs others and how it makes the "pro" mark? I eagerly await your replies.