AF Availability When Using Teleconverters

[Brendan Dozier]

I'm using a 7D and have Canon Extender EF 2x II teleconverter, and thinking of renting a Canon 500 or 600 lens. Understand from last post that AF performance is effected substantially when going from 1/4 x to 2x teleconverter.

In terms of renting a lens: When using teleconverters, both 1/4x and 2x, is there any difference in AF limitations between the older and newer Canon lenses 500 and greater?



Appreciate clarification on this,

- Brendan

[Ronald Zigler]

Brendan, I called Canon last week to ask them about this very issue. I was under the impression that if I am using a Canon 60D, the 300mm f4L lens would not auto focus if it was used with the Canon 2x teleconverter. This is not entirely accurate, and the Canon lens brochure about this matter is dated and misleading (it indicates no auto focus with this lens and TC with most Canon bodies). I was informed that if I used the 300mm f4 with the 2x TC, I would indeed have auto focus but only in the "Live View" shooting mode. It would seem to me, that at the very minimum, you would also have auto focus in the Live View feature on a 7D.

[Brendan Dozier]

I modified my question after reading the last post. Thanks Ron, that is interesting, and kind of frustrating because I'd much rather have AF work in viewfinder mode.

I did rent a Canon 600 earlier, and the AF was completely unavailable when using my 2x. but thought the AF was not working because of some mistake I had made with the settings. It did work without the 2x, so I was able to get some images. When I told the guy at the store later, he had no clear answers, and was led to believe it was probably an error on my part.

[Roger Clark]

Brendan,

Only existing 1D series cameras will AF at f/8 with viewfinder AF (phase detect AF). Ronald is correct that you can use live view to AF. That will give AF for static subjects, but will not work for BIF or other moving subjects. You could have used that on the 600 with your 7D. For f/4 lenses and AF tracking, best to get a 1.4x TC.

Roger

[Doug Brown]

Ditto what Roger said.

[Brendan Dozier]

Only existing 1D series cameras will AF at f/8 with viewfinder AF (phase detect AF).

Is this without a teleconverter?

Just want to clarify: Viewfinder AF is available with 7D with 500/600 + 1/4 x?

What about 7D + Sigma 300-800?


Thanks Roger

[Roger Clark]

Is this without a teleconverter?

Just want to clarify: Viewfinder AF is available with 7D with 500/600 + 1/4 x?

Yes, viewfinder (phase detect) AF is available on all canon DSLRs at f/5.6, including 500/600 + 1/4 x.

What about 7D + Sigma 300-800?


Thanks Roger

Not sure what the Sigma 300-800 f/ratio is. But it is simple: viewfinder AF will work at f/5.6 and faster, but not at f/8 on the 7D and all other canon consumer DSLRs. Viewfinder AF at f/8 only works on 1D series except for the latest 1DX which is not out yet. Also, the existing 1D series will AF with stacked 1.4 and 2x TCs (even canon TCs). The new canon TC III models will not stack unless a spacer is included.

Some third party TCs do not report data so AF will work on consumer grade DSLRs. Note that whether 1D or consumer grade, f/8 and slower AF is more difficult and if the contrast is low even in bright light, there will be more error. And at low light f/8 and slower will be more AF error.

One can also tape over some pins on Canon TCs to get them to AF at f/8. You can probably find it online as I've not done it (seems like it could mess up the connection with glue).

Roger

[Roy Churchill]

Out of interest recently I was trying a 400/5.6 with both a 1.4x tc (f8) and a 2x tc (f11) in live view AF mode and they both worked fine but as already been said AF is relatively slow so only OK for near static birds, you also need good contrast.
Another interesting thing about live view AF is the 2x tc I was using was a very old teleplus (now Kenko) one that is optical very good but would not AF with any of my f2.8 lenses (probably needed re-chipping) but it was fine in live view AF. As I see it providing you have good light and contrast there is no limit as to the aperture that Live view AF will work at.

[Brendan Dozier]

Thanks Roy, I may try out the AF with the Live View on slow moving subjects and see how it goes.