200-400 I know a guy who shot CART with one...... he ended up upgrading to a 400mm f5.6 L lens because he "hated" it..
As for the others, ...just buy the brand lenses.... My friend Dan sent his 70-200 HS APO Sigma lens to get rechipped because of incompatability issues.....well, the repair time has been so long that ended up buying a Canon 70-200 f2.8 L.. It has been 4 months ago and he calls them all the time asking when it will be ready....
The thing is....is that those lenses cost less...but you suffer in some way because of it.. I just have Canon lenses... I learned my lesson before I switched from Minolta to Canon back in 96.. I had Sigma, and Tamron lenses... I even owned the Tamron 300mm f2.8...I still have a picture on my wall that a friend took with me holding it in my army jacket.. I later bought a 300mm f4 IS lens and that was faster and more accurate with the AF than my Minolta Maxxum 9xi and the 300mm f2.8 lens... It didn't have full time manual focus over ride but it was white....so at least I looked cool from a distance [img]/ubbthreads/images/graemlins/wink.gif[/img] Oh, and as for sharpness...... it was nothing great... I love my 300mm f2.8 L lens so much more... I am glad to have bought the better lens.....
Seriously, you really do get what you pay for..
JP
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