Canon AF question for a friend

[shane shacaluga]

A friend of mine just upgraded from a Canon 550D to a 6D

He recently bought an extender 2x III and along with his 100-400 canon lens it managed to AF (slowly but it worked ok)

Now he has tried on the 6D and the AF wont work

Any ideas why an older less advanced camera would work and the 6D won't?

Thanks

[David Stephens]

Luck. It wasn't designed to work at that small aperture.

[Daniel Cadieux]

That lens and body combo should not have AF'd with a 1.4x let alone a 2x. Must have been pretty much unusable.

[shane shacaluga]

He must be a lucky guy then haha. He mentioned it worked "ok" for perched birds etc