5D MK III, 300mm f/4 & 2x TC?

can anyone with a 5D MK III (latest firmware version) and a 300mm f/4 plus a 2x TC, confirm or deny wether AF functions at all please?

from This Canon web page it appears it should, but I'd be interested to hear from anyone that's used this combination.

thanks.

As long as the 5D3 has had the firmware update it will AF up to f/8. I've used a few f/5.6 lenses with a 1.4x converter and it worked perfectly. I have a Canon MkIII 2x converter but the only lens I use it on at present is a 70-200 f/2.8 IS MkII but I have used a Kenko Pro300 DGX 2x with my Canon 24-105 f/4 IS and that worked perfectly with my 5D3.

It should certainly auto focus, though it will be slow.
Coincidentally I and a friend were reviewing some images of Dunnocks (little brown jobs) last night and I was surprised at the quality of his images. We both use Canon 1D4 cameras but I was using a 600 F4 L IS and he was using a 300F4 L IS + a Mark 3 2 x extender. The images were not as good as those taken with the 600mm but they were more than usable. Note this is with the Mk3 extender - my Mk2 wasn't up to much.

Hello, Joseph

Yes it does work, at least on my 5D Mk III, Canon 300mm F4 L and x2 Canon Extender EF II. I tried it after the firmware upgrade and pointed the 600mm F8 combo out of the back window just to trial the AF – I didn’t save any images for analysis.

From memeory, only the centre AF point was selectable and I recall thinking at the time that this set up would probably not be useable for e.g. bird in flight due to the somewhat slow AF.

On the contrasting dark green/white fencepost, the AF seemed snappier than on the lower contrast tree bark images I tried.

Cheers

Dennis

thanks for the answers guys - I have someone interested in buying one of my 2x TC's & he was a bit dubious that it wouldn't work at all.

cheers.