Canon EF 100-400 MkII doesn't play well with Canon extender 1.4 MkII and Canon 6D?

I am asking the question on behalf of a friend. He has the Canon 6D and the EF 100-400 MkII.

Recently he bought a (used) Canon extender 1.4 MkII.

The AF is not working.

My reaction was that with the EF100-400 MkII combined with the extender has maximum apertures beyond f5.6 and he should not expect it to AF with the 6D.

As far as I know, only the 7DII and the 1Dx will AF with with this lens/extender combination (I am not sure about the 5DIII) to f8.

What are the possible options?

a) Tape the contacts?

b) Will the MkIII extender work?

c) A new(er) camera? Will the 5DIII or the 80D work?

I don't think a EF 600 is in the cards....

MakisM1 wrote in post #18096395
I am asking the question on behalf of a friend. He has the Canon 6D and the EF 100-400 MkII.

Recently he bought a (used) Canon extender 1.4 MkII.

The AF is not working.

My reaction was that with the EF100-400 MkII combined with the extender has maximum apertures beyond f5.6 and he should not expect it to AF with the 6D.

As far as I know, only the 7DII and the 1Dx will AF with with this lens/extender combination (I am not sure about the 5DIII) to f8.

What are the possible options?

a) Tape the contacts?

b) Will the MkIII extender work?

c) A new(er) camera? Will the 5DIII or the 80D work?

I don't think a EF 600 is in the cards....

1D*, 5DIII and 7DII w/ firmware update are the only cameras in the lineup, that I'm aware of that support f/8 AF (80D is new enough that it *might*). Only options I can think of would be be trying taping the pins [But don't expect to hit focus on anything moving] or pick up a camera that supports the f/8 AF. The function is controlled by the camera, not the TC, so the MkIII won't work any better/different.

I own the 1DX and 7D2 and both AF reasonably well with the 100-400 Mk2 and 1.4 (Mk3) extender as will the 5D3 with up to date firmware. Unfortunately I believe that your 6D does not support this.

Having said that it would be worth taping the pins and giving it a try. I had little success with earlier bodies but, given the 6D's low light AF abilities, it is well worth a try.

Realistically though I wonder if it is worth getting another body just for this function, it's nice to have but not critical IMO with this lens.

80D would work, it has AF at f8. (I'm using the 80D + 100-400 MkII + extender 1.4 MkIII)

Low light AF capability isn't the same thing as f/8 max aperture AF capability. It's not the less light coming in that's the problem. There's much more light available in daylight with f/8 than at dawn with f/1.4. The problem is instead the short baseline, i.e. the physical width of the aperture opening.

(A) "You" can tape "the" contacts on some KENKO TC's--- Not sure about the Canon?

(B) The 1.4lll is no different as to F8 AF-- That's down to the Camera body.

(C) Both the 5Dlll, & 80D have F8 AF, as does the 7D-2, but the 80D, & 7D-2 are 1.6X, Crop/APS-C cameras.

Ok! Understood.

Thanks everybody.

I tried the taping method. Don't even bother. All it does is hunt.


If you keep trying to focus on the same spot for 6 or 8 tries it might lock on.

Just get the equipment that will do the job you need to do.

I tried to use the 6D with Kenko and Tamron TC's. They worked, but the AF hunted a lot, and was successful only in bright daylight, so I got rid of them, not worth the trouble. The Canon version, both II and III, would not at all, as many stated here.