topic Re: EOS R6, EF 100-400mm f/4.5-5.6L IS II USM: Extender EF 1.4X III Switches To Manual Focus in EF & RF Lenses

EOS R6, EF 100-400mm f/4.5-5.6L IS II USM: Extender EF 1.4X III Switches To Manual Focus

wushuyvr — Thu, 03 Oct 2024 21:33:33 GMT

Hi everyone,

I’m having an issue with my Canon R6. I’m using it with an RF to EF Adapter, a 1.4 Extender iii, and an EF100-400 mk ii lens. When I first turn the camera on, everything works perfectly, and it focuses as it should. However, after a few shots, it suddenly switches to manual focus (MF) on its own.

Has anyone else encountered this problem? Any ideas on why it’s happening or, better yet, how to fix it? I’d appreciate any insights!

Re: EOS R6, EF 100-400mm f/4.5-5.6L IS II USM: Extender EF 1.4X III Switches To Manual Focus

deebatman316 — Thu, 03 Oct 2024 21:48:46 GMT

Does the lens work correctly with the teleconverter removed. Also if you have a DSLR will it work correctly on there. Does the camera still report aperture when this happens or does it report F/00 or F--.

Re: EOS R6, EF 100-400mm f/4.5-5.6L IS II USM: Extender EF 1.4X III Switches To Manual Focus

wushuyvr — Thu, 03 Oct 2024 22:05:39 GMT

Hi deebatman316,

when I take off the extender, the ef100-400 mk ii works and focuses as it should. That’s why I’m thinking the issue is with the extender.

Re: EOS R6, EF 100-400mm f/4.5-5.6L IS II USM: Extender EF 1.4X III Switches To Manual Focus

deebatman316 — Thu, 03 Oct 2024 22:13:05 GMT

Does it work on a DSLR camera properly. To remove the adapter from the picture.

Re: EOS R6, EF 100-400mm f/4.5-5.6L IS II USM: Extender EF 1.4X III Switches To Manual Focus

p4pictures — Fri, 04 Oct 2024 06:43:38 GMT

If you can, then try swapping the mount adapter out for another one. I have seen odd issues with a Canon mount adapter in the past myself.

Re: EOS R6, EF 100-400mm f/4.5-5.6L IS II USM: Extender EF 1.4X III Switches To Manual Focus

ebiggs1 — Fri, 04 Oct 2024 15:23:17 GMT

"I’m using it with an RF to EF Adapter, a 1.4 Extender iii, ..."

Both are Canon brand accessories? If not that is your problem.

Re: EOS R6, EF 100-400mm f/4.5-5.6L IS II USM: Extender EF 1.4X III Switches To Manual Focus

Ceddy — Thu, 10 Apr 2025 16:59:11 GMT

Hi, sorry, I am new to the forum. I am researching extenders, and I have that lens as well. I looked at that extender's compatibility with EF lenses. For some reason, it says it's compatible with the EF100-400mm usm, however the mkii is not on the list. I'm wondering if you found out if that was your issue? I found it odd that the mkii wouldn't be compatible if the version 1 was?

Re: EOS R6, EF 100-400mm f/4.5-5.6L IS II USM: Extender EF 1.4X III Switches To Manual Focus

p4pictures — Thu, 10 Apr 2025 17:46:28 GMT

I have the EF 100-40mm f/4.5-5.6L IS II USM lens, the EF Extender 1.4x Mk III, use them on the Canon standard plus control ring mount adapters. I use the combination with EOS R6, EOS R6 Mark II and EOS R10. There is no problem and it all works.

Re: EOS R6, EF 100-400mm f/4.5-5.6L IS II USM: Extender EF 1.4X III Switches To Manual Focus

wushuyvr — Thu, 10 Apr 2025 17:52:36 GMT

Yes the lens works correctly when the teleconverter is removed.

Good idea though to try it on another body to see if the same thing happens. I'll give that a try.

Re: EOS R6, EF 100-400mm f/4.5-5.6L IS II USM: Extender EF 1.4X III Switches To Manual Focus

deebatman316 — Thu, 10 Apr 2025 18:03:25 GMT

Also try a different Canon brand teleconverter too.