Hi Kenneth,

I haven't yet. I had a vacation in March that could have involved a long lens. But we opted to go to Portugal instead, so the urgency has subsided a bit. Next up is Yellowstone in early September, loons from a kayak in July, and maybe getting more into backyard birding. So, in my spare time ( ), I am considering how best to set up my kit in the supertele range.

BTW, regarding your original question, I have used the 2x TC III with the 70-200 II on my 5DIII. It was good enough to capture some images that made it into an album. But AF/contrast do suffer a bit. Thus, I'd consider it on an "as needed" basis.

Thanks,
Brant