Focusing question

[Pozo]

I will be renting the 400 5.6L lens and the 1.4 tele extender in the near future to have some fun with wildlife photography. My camera body is the T3i. With the extender on, my maximum aperture will be f8. Does anyone know if the T3i is capable of autofocusing at f8 with the center point? I couldn't find this answer in the manual. My intuition is that only the pro level bodies can autofocus at f8.

I will be renting the gear either way, but it would be sweet if i could have a little autofocus help with the extende on.

Thanks forum!

[MikeSowsun]

The T3i will not AF normally at f/8 but I have read that you can tape over some of the teleconverter contacts to fool the camera and then get some AF capability.  

Canon tape trick f/8 autofocus

[TCampbell · Accepted solution]

There are only two Canon DSLR bodies that support auto-focus at f/8... the 1D X and the 5D III.  

The camera doesn't focus at f/8 because it cannot focus reliably at f/8.  It's extremely difficult for DSLRs to focus at higher focal ratios (it's actually even difficult for a photography to manually focus a 35mm film camera at f/8... the prism isn't getting light from wide enough angles to work effectively.)

You can do "live view" if you have plenty of light becuase that uses contrast-detection to focus instead of phase-detection -- so there's no prism involed.  But of course it's also not as fast.

On your side, however, I think the 400 f/5.6L has a focus-memory button (my 300mm f/2.8L does).  If you find a location where you expect the wildlife to appear (e.g. say a bird returning to its nest) you can pre-focus the lens on that location and hit the focus-memory button.  When the animal actually DOES return and it's time to take the photo, you can just hit the focus-recall and snap the shot -- confident that the lens will return focus to the exact position you pre-focused earlier.