I have both the EX1.4 II and also the EX 2 iii and used them on my 70-200l 2.8 is II. I found the EX 1.4 OK but was not happy with the EX2 results. I found at fully zoomed that the EX 1.4 was acceptable but the EX 2 was not as good as expected and just not sharp enough.

I just purchased the ef 400mm 5.6 for this exact reason as I wanted the best quality images. I thought about the 100-400 but the image quality gain was not enough compared to the 400l 5.6 and already had the 100-200mm covered by the 70-200 with far better lens then 100-400. The price and quality for the 400mm 5.6 was a no brainer as the next step is 400l 2.8 and do not use it enough to justify the price. Another thing I did not like about extenders is that you always have to add it so makes switching more time consuming and could loose that OMG shot.

Check out the reviews on this site for excellent reviews and also look at http://www.luminous-landscape.com/index.shtml as he also has compared and reviewed them. I also found that I got the best information from this site and forums compared to any others I have visited etc.

Cheers

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