What's the best price quality 2x TC for this lens ?
Is the competition also good like the Sigma & Tamron, is there any test online with Teleconverter comparison of the latest 2x versions ?
It's to have some more tele for soccer games, as long as the zoom still works, AF, sharpness stays good.
The Canon Extender EF 2x III or is the competition getting better at more interesting prices, like the Sigma Art series in the lens categories 
Kenko seems to be well known also, I saw even a 3x exist, but then i'll lose too much light I think 
Are most without losing AF ?
) but the small,worthwhile, AF improvement and the major advance in IQ make the Mk3 a significant upgrade IMO. A friend, who has the Canon 600 F4 L IS Mk1, would not buy a 2 x extender until he tried the Canon 2 x Mk3 - he bought one within a couple of days!
