Canon 6D + 70-200 F4 + 2x TC. AF maintained or not ?

I think a lot will depend on which TC you're using Mike. If you get a Kenko Pro300 DGX converter you might be lucky enough to get away with it. I retained a good level of AF and IQ with a Kenko Pro300 DGX 1.4x TC on a Canon 100-400 L with 550D, 7D, 60D and a 5D2 bodies and they were all f5.6 AF bodies that AF'd at f8 and all reported correctly. I doubt you'd get away with it on a Canon TC at the moment, but if the forthcoming firmware update for the 5D3 is successful Canon will probably filter it through to a new firmware for the 6D soon enough.
 
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Ah - that's very interesting Stuart, thanks very much!

I had though it would be more likely to work with a Canon 2x tc so it's good to know it's the other way around.

I really fancy an F4 70-200 IS as it's meant to be great and is cheaper, lighter and smaller than the F2.8 but I'd like to use a 2x tc for occasional wildlife shooting hence the dilemma :)
 
I had both Canon TC's - the 1.4 and the 2. The 1.4 costs one stop and the 2 costs two stops. AF only works at apertures of 5.6 or lower. So on a F4 lens the 1.4 will give AF but the 2 will not. On a 2.8 lens both give AF.

However the Canon converters are only compatible with a limited number of Canon lenses (see Canon site for details). Canon are however the best TC's out there and IMO there is virtually no difference in the sharpness of photos when they are used.
 
valb said:
I had both Canon TC's - the 1.4 and the 2. The 1.4 costs one stop and the 2 costs two stops. AF only works at apertures of 5.6 or lower. So on a F4 lens the 1.4 will give AF but the 2 will not. On a 2.8 lens both give AF.

However the Canon converters are only compatible with a limited number of Canon lenses (see Canon site for details). Canon are however the best TC's out there and IMO there is virtually no difference in the sharpness of photos when they are used.
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Thanks Val - I don't think it is quite as clear cut as that though (see above reply from Stuart) :)
 
This is my understanding of how things work:
Reporting TCs: A TC-compatible lens (e.g. 400/5.6) detects the presence of a TC through the extra contacts and reports the correct f-stop for the combination to the camera.

Non-reporting TCs, or taped TCs, or TCs with non-TC-compatible lenses: The lens does not detect the TC and just reports its own f-stop. AF may still work, because the camera doesn't know about the true f-stop, and tries to AF even if the combination is outside the specs.

Kenko DGX: Unlike the above TCs, the DGX manipulates the communication between the lens and the body so that the f-stop is always reported correctly for the combination, and so that AF is retained even if the combination is above f/5.6. From your and others observations that f/8 is reported but AF still works, my guess is that wide-open f-stop and used f-stop is reported separately and the camera looks at the wide-open f-stop to determine if it should try to AF.

Personally unless you have fantastic light conditions a 2X TC on either of your lenses won't produce great results. Canon limit autofocus to f5.6 for all but there 1D series camera's, and it also depends on the compatibility of the lens with the TC as only certain lenses work.

TCs are really designed for the faster prime lenses not zooms because the optics can handle the drop off in image quality and hit on the auto focusing, but you can use a zoom and TC but be aware you'll need decent light conditions to get anything worth while image wise
 
I speak from my experience of using both the Canon TC's on a 70D and a 600D with a 70-200 F4 IS lens and a 100-400F4 IS lens and I can assure you that what I stated above is exactly what I experienced and also what the Canon web site confirms. I cannot comment on non Canon TC's as I have never used them.
 
Strangely, I think this is down to the lens (and not aperture-wise) more than anything. My 100-400 used to focus fine with a Kenko 1.4 on my 7D, then I sent the lens off to Elstree for an extensive service (they did so much work it got a new serial number) and when it came back as new, it completely refused to focus with the 1.4, which makes me think that older lenses (age not model) are more likely to focus with teleconverters. It may, of course, have been a coincidence, but it is quite a strange one if so!
 
pete.rush said:
This is my understanding of how things work:
Reporting TCs: A TC-compatible lens (e.g. 400/5.6) detects the presence of a TC through the extra contacts and reports the correct f-stop for the combination to the camera.

Non-reporting TCs, or taped TCs, or TCs with non-TC-compatible lenses: The lens does not detect the TC and just reports its own f-stop. AF may still work, because the camera doesn't know about the true f-stop, and tries to AF even if the combination is outside the specs.

Kenko DGX: Unlike the above TCs, the DGX manipulates the communication between the lens and the body so that the f-stop is always reported correctly for the combination, and so that AF is retained even if the combination is above f/5.6. From your and others observations that f/8 is reported but AF still works, my guess is that wide-open f-stop and used f-stop is reported separately and the camera looks at the wide-open f-stop to determine if it should try to AF.

Personally unless you have fantastic light conditions a 2X TC on either of your lenses won't produce great results. Canon limit autofocus to f5.6 for all but there 1D series camera's, and it also depends on the compatibility of the lens with the TC as only certain lenses work.

TCs are really designed for the faster prime lenses not zooms because the optics can handle the drop off in image quality and hit on the auto focusing, but you can use a zoom and TC but be aware you'll need decent light conditions to get anything worth while image wise
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Great reply Pete, thanks :thumbs:
 
valb said:
I speak from my experience of using both the Canon TC's on a 70D and a 600D with a 70-200 F4 IS lens and a 100-400F4 IS lens and I can assure you that what I stated above is exactly what I experienced and also what the Canon web site confirms. I cannot comment on non Canon TC's as I have never used them.
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Val - thanks, I wasn't meaning to cast doubt on your comment so please accept my apologies if this is how it came across :)
 
So is it safe to say, that if your happy to lose a fraction of sharpness, the Kenko extender is the way to go, as its more likely to give you AF?
 
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