Happy with tubes
I like to place a Kenko tube behind my 70-200 2.8 and 300 f/4 for macro purposes. If I use one tube at a time auto focus is spot on. When stacking two or more tubes auto focus is jumpy and focus searches more. The release button is a little too easy to engage while mounted which makes it problematic for your lens slipping off. You just have to assure to keep your hand /fingers off of that button. Otherwise great bargain.
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