Are these converters slower to focus than the raw lens?


I have read in many forums that they are 66% slower due to intentional slow down by Canon.


Can someone give me a definitive answer on this?


I have also read that the Kenko 300 pro is not slowed down and therefore faster and a better choice than the Canon brand.


I would love to know the true answer to this...not just unsubstantiated rumor thrown around.





Thanks for any help (esp since I just bought a 1.4 and 2.0 Canon for my 300 2.8)





Peter