Quote Originally Posted by neuroanatomist
do agree that the MkII seems to give much better results with the extenders than the MkI. But, be a little cautious about judging the performance with extenders across the zoom range - at least in Bryan's tests, the extenders are only tested at the longest end of the zoom.

Personally, I prefer cropping to extenders. Sure, you lose megapixels, but if I crop the 70-200, I still get a 400mm 5 megapixel image, and there is no additional loss of IQ due to the extender iteself (though this may be negligable for all I know).


If cropping is your "extender", there is never a need to do it except at the long end. This is why for me, IQ at the long end is most important.