I cannot get the Autofocus to work with a Canon EF 1.4X III Extender and a Canon 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.