Agreed. Canon has stated that there is a 50% drop in AF speed (imposed by the firmware as a trade off for accuracy) with a 1.4x TC, and a 75% drop with a 2x TC. That sounds worse than it is, because Canon is referring to the speed at which the focusing group is moved, but the distance the focusing group needs to move is also reduced with an extender in place, so overall the AF performance hit is not too bad. Still noticeable in my experience, though (in spite of claims from a Canon mouthpiece that it shouldn’t be).in addition and to support what Alan just said, there is also a noticeable AF performance toll associated with teleconverters that is mostly noticeable in poor light conditions. not so bad in case of x1.4 teleconverter though but still noticeable
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