EOS Rebel T3i AF functionality with EF 1.4X III Extender and EF 100-400 4.5-5.6L

[wcarter]

Anyone know if the Autofocus will work with a Canon EF 1.4X III extender and a Canon EF 100-400 4.5-5.6L lens on a T3i? The compatibility chart says they will work together, but my T3i switches to manual no matter what I do.

[cicopo]

Not going to work That body can't AF at F8 which is now the widest aperture for the lens & TC combo.

[diverhank]

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@wcarter wrote:
Anyone know if the Autofocus will work with a Canon EF 1.4X III extender and a Canon EF 100-400 4.5-5.6L lens on a T3i? The compatibility chart says they will work together, but my T3i switches to manual no matter what I do.

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Auto-focus will not work, not because the EF 1.4X III is not compatible but because the combo raises the minimum aperture to f/8 - you lose 1 stop using the 1.4 teleconverter and with the 100-400mm being at f/5.6 that becomes f/8.

Some higher end Canon cameras such as the 1D series, the 5D mark III/IV and the 7D Mark II (not sure about the 6D) will auto-focus at f/8 but the Rebels won't.

The workaround would be to tape the 3 pins on the teleconverter and fool the camera into letting you focus (no f/8 report).  You can google the instructions easy enough.  The Autofocus performance may or may not be satisfactory though.  There is a reason why Canon disallows auto-focusing at f/8.

[wcarter]

Thanks to Cicopo and Diverhank for thier help on this issue.  Maybe it is time for a full sensor Canon.

wcarter

[cicopo]

The 7D mark 2 can AF with that combo. May only be the center AF point or expanded center set but it can AF.

[Waddizzle]

The 80D center point can focus at f/8, too.  It's nearly a 7D Mark II, minus the weather resistant build.

[markophoto]

Just to update on this discussion, when the 1.4x extender is used with the Canon 5D mk iii along with the EF 100-400 4.5-5.6L USM ii lens, the firmware on the camera must be 1.2.1 or above, otherwise the autofocus wont work.  Firmware update 1.2.1 enables the autofocus when used with an extender and 'certain' lenses.  Current firmware at the time of writing is 1.3.6 which I have just updated to and it has fixed this autofocus issue.

[p4pictures]

Probably the firmware was updated to make use of the new lens + extender combination that didn't exist when the camera was introduced. The EOS 5D Mark III was announced in March 2012, and the EF 100-400mm f/4.5-5.6L IS II USM was announced in November 2014. MkIII extenders were announced in 2010.