Whoa, this one puts a smile on my face. I have been advising for more than a decade that folks NEVER put a UV filter on a telephoto lens. It degrades quality and often kills AF performance. See same in ABP II.

Best part is as I was reading the thread I never even thought UV filter... It's a basic.

I wonder how many of the interet experts trashing the 100-400 have/had UV filters (recommended by their friendly camera store salesman) on their lesnses...

Man, you gotta love it.