[nater]

thanks for the advice on the TC..that puts that idea out of the equation. ive only used TC's on manual lens and have never had experience with AF and TC...cheers

I bought the Tamron 70-200mm specifically for dual use, both without a teleconverter for indoor and people shots, and with a teleconverter for airshows. I have three PZ-AF teleconverters, the 1.5x Kenko, 1.7x Promaster, and 2x Tokina (which appears to be a rebranded Kenko). The one airshow I've shot I was happy with the results of the 1.5x Kenko. Sharpness was very good, and no excessive chromatic aberration (in fact it was far below what I would have seen with the Tamron 70-300mm f/4-5.6). I think the effective 100-300mm f/4 works well for shooting an airshow. I think it would have been potentially useful to have the extra reach of the 1.7x, however I had issues with getting a sure focus lock on some objects with that teleconverter, so I had to go to the 1.5x, which didn't give me any trouble and I shot with for most of the day. I haven't tried the 2x yet, but I expect it will only useful in manual focus situations or perhaps specific subjects in specific lighting situations with certain lenses. I wouldn't discount the use of a 1.4x or 1.5x teleconverter with a lens like the Tamron 70-200mm f/2.8.

[Tommot1965]

ended up with a 70-200 HSM II sigma...go figure...it was a good price and Local....it will do me until I can buy the optically superior Sigma OS 70-200