Remember that you can not use the Canon's original 2x TC with either lens as it won't physically fit. I don't know for sure about 1.4x though.
As for AF, as long as your final F stop is less than 5.6, you should be able to have the benefit of AF, but even at best with canon's Mark II 2x tele-extender, I see a significant drop in AF performance even with 70-200mm L 2.8 IS.
General rule of thumb; Reserve TC only for few occasions. If you need the final focal length for routine use, consider buying that focal length in first place.
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S a s s a n .
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"No one is going to take our democracy away from us. Not now, not ever.
" JOE BIDEN
Last edited by sassan; 05-04-07 at 05:36.
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