Will EF 100-400 mm F/4.5-5.6 L IS USM EF autofocus on EOS Rebel T6i?

[LLF]

Will the auto focus feature on this lens work with my Canon Rebel EOS T6i

[deebatman316]

Yes all Canon brand EF & EF-S lenses will autofocus on your camera. Also IS will work on your lens.

[shadowsports]

Greetings,

Yes it will.  

[ebiggs1]

More of a curious question, why did you think it wouldn't?

[LLF]

When I attach the lens extender on the lens everything fits just fine on the camera but the autofocus feature doesn’t work. 

[deebatman316 · Accepted solution]

Your camera cannot AF with an aperture smaller than F/5.6. Only a few DSLR & SLR cameras can AF at F/8. Those are the EOS-3 (EOS 35mm AF SLR), EOS-1V (EOS 35mm AF SLR), EOS-1D, EOS-1Ds, EOS-1D Mark II, EOS-1Ds Mark II, EOS-1D Mark III, EOS-1Ds Mark III, EOS-1D Mark IV, EOS-1D Mark II N, EOS-1D C, EOS-1D X, EOS-1D X Mark II, EOS-1D Mark III, EOS 5D Mark III, EOS 5D Mark IV, EOS 5DS, EOS 5DS R, EOS 6D Mark II, EOS 7D Mark II, EOS 90D, EOS 80D, EOS 77D/ EOS 9000D & EOS Rebel T8i/ EOS 800D/ EOS Kiss X10i. Are the ONLY SLR and DSLR cameras that can AF at F/8. Mirrorless cameras such as Canon's EOS R series lineup don't have this restriction. 

[LLF]

Thank you very much. 

[normadel]

Lens extenders, first of all, are not recommended for all lenses. Canon's manuals for lenses tell you this.

Here is yours: https://gdlp01.c-wss.com/gds/7/0300003647/02/ef100-400f45-56lisusm-im2-en.pdf

Page 14 explains things clearly.

An extender causes a smaller effective aperture, so there isn't enough light for the camera to focus with. A 1.4x extender may be okay, but a 2x won't be unless a lens has a large aperture to begin with.  So manual focusing is required.

[LLF]

Thank you for your help