5d mkiii and no AF at F8

[gary]

I have read a review on Photo net of the 5d mk 3. In it it was said that there is "no AF at F8 as was the experience with the 1DX. As the review was dated 25th July, I am somewhat confused, I have a mk 3 and I don't seem to have a problem. Does anyone else know if this is right, just curious. 

[wickidwombat]

its no AF for lenses or combos at maximum aperture of f8

[neuroanatomist]

All cameras autofocus wide open, and then stop down to the selected aperture just before exposure.  Plus, the issue is with a lens wide open.  Since basically all current autofocus lenses are f/5.6 for faster, or at least they tell the camera that, the limitation really only applies when using slower lenses with teleconverters.

The reason it's mentioned, especially in connection with the 1D X, is that previous 1-series bodies had the ability to AF at the center point with an f/8 combo.

[gary]

Thanks for that now its clearer

[heptagon]

Unfortunately you cannot use the 70-200 F4 or 300 F4 together with a canon 2x Extender on the new cameras.

Third party extenders may trick the camera into thinking it is a F5.6 lens while focusing but switch to correct data just before taking a picture. And focusing works mostly OK at F8 in good light. So the cameras really are capable of focusing at F8 under good conditions but Canon disabled it because people would complain and didn't give us an option to enable it again.

[marekjoz]

Unfortunately you cannot use the 70-200 F4 or 300 F4 together with a canon 2x Extender on the new cameras.

Third party extenders may trick the camera into thinking it is a F5.6 lens while focusing but switch to correct data just before taking a picture. And focusing works mostly OK at F8 in good light. So the cameras really are capable of focusing at F8 under good conditions but Canon disabled it because people would complain and didn't give us an option to enable it again.

You can cheat the camera by using a scotch tape telling it's not f8 but lower. 70-200 f4 is with ef 2.0 II doesn't focus anyway on 7d or 5d2 even after fooling the camera. Has anyone checked this with 5d3?

[Mt Spokane Photography]

Unfortunately you cannot use the 70-200 F4 or 300 F4 together with a canon 2x Extender on the new cameras.

Third party extenders may trick the camera into thinking it is a F5.6 lens while focusing but switch to correct data just before taking a picture. And focusing works mostly OK at F8 in good light. So the cameras really are capable of focusing at F8 under good conditions but Canon disabled it because people would complain and didn't give us an option to enable it again.

You can cheat the camera by using a scotch tape telling it's not f8 but lower. 70-200 f4 is with ef 2.0 II doesn't focus anyway on 7d or 5d2 even after fooling the camera. Has anyone checked this with 5d3?

I've found it varies by individual camera / lens combination, and not necessarily by model.  Some may have the internal gain higher than others, or just be a mite more sensitive.  Some note that TC's from another manufacturer worked for them too.
There are lots of reports from 5D MK III users, and they conflict.  I tested several lenses with  Canon TC's on my 5D MK III with taped pins, and stacked TC's.  Some worked slowly, some zooms worked only zoomed out, and most had issues near MFD.
Just because a person found something worked or did not work for them does not mean your results will be the same.

[smithy]

We'll just have to manually focus, won't we?