Originally Posted by btaylor
That would be correct!
The AF speed is still very useable, as you mentioned 75% slower X very fast is still fast.
The AF speed reduction as reported by Canon, has to due with the smaller aperture of f/5.6 as well as the reduction in IQ from the extender.
By the way, in case you weren't aware, the 1.4X extender has a 50% reduction in AF speed.
Rich




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