I frequently use this lens with a Canon 1.4 tc on a 350D. To achieve AF you must tape the last three pins on the converter thus fooling the camera into thinking there is no TC present. The only TC which will achieve AF without taping the pins (on a non 1 series body that is) is the cheap 4 element Kenko/Tamron but trouble is this is a poor quality converter.
AF with the pins taped can be a lot slower than normal and will sometimes 'hunt' quite a bit. I have found there are a few ways of overcoming this:-
1) By manually focusing near enough and then using the AF for the final focus.
2) When the AF starts to 'hunt' take your finger off the shutter release and depress again - it will almost always lock on right away by using this method.
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