I've been using my Tamron 17-50 for a few years now to shoot weddings, social events & portraits and I love the image quality but I lack confidence in it's focus accuracy under certain circumstances and I'm trying to determine if a lens or technique upgrade would give better results. The times I have the most issues are when focusing on more distant objects, from full body length @ 35mm and greater distance (including @ infinity), to the extent that I'm not comfortable shooting at f2.8 because I'm not certain it will focus accurately enough to be sharp. I'm mostly using the lens on a 50D and see the problem with both centre and outer focus points. I have the camera set-up to only focus with the AF button on the back and I typically use servo autofocus. I guess my questions are: Is there an issue with my technique that could be causing the issues? Have other experience similar issues with the Tamron? Does the Canon have been focus accuracy in the conditions I outlined above? Thanks!