topic Re: EF 100-400 Auto Focus does not work. in EF & RF Lenses

EF 100-400 Auto Focus does not work.

ccobb66 — Tue, 27 Jul 2021 03:20:15 GMT

I have an EF 100-400mm f/4.5-5.6L IS USM. The Auto Focus does not work. When I turn the camera on the letters MF flashes in the window on the back. The lens is set to AutoFocus and when I change it to ONE SHOOT or AL SERVO it flashes a message that says "Set the focus mode switch on the lens to AF" which it is already there. If I switch the lens to MF - it does not flash.

Re: EF 100-400 Auto Focus does not work.

jrhoffman75 — Tue, 27 Jul 2021 11:52:32 GMT

Welcome to the forum.

From your description it sounds like the switch has possibly failed.

Try cycling the switch a few times to possible clean contacts.

Also remove and replace the lens a few times as well.

If that doesn't resolve the problem it will probably need service.

Re: EF 100-400 Auto Focus does not work.

ebiggs1 — Tue, 27 Jul 2021 14:45:42 GMT

"... it will ~~probably~~ need service." Sorry.

Re: EF 100-400 Auto Focus does not work.

ccobb66 — Tue, 27 Jul 2021 15:10:36 GMT

Thank you. That is what I thought also.

Re: EF 100-400 Auto Focus does not work.

ebiggs1 — Tue, 27 Jul 2021 15:25:45 GMT

"When I turn the camera on the letters MF flashes in the window on the back."

This tells you it isn't any contact(s). It is making connection for that to happen. Hopefully is it just the AF/MF switch. That will be an easy and fairly inexpensive fix. Plus your lens will come back looking brand new. Canon will also check out the rest of the lens to new specs.

Re: EF 100-400 Auto Focus does not work.

Waddizzle — Tue, 27 Jul 2021 16:48:56 GMT

@ccobb66 wrote:
I have an EF 100-400mm f/4.5-5.6L IS USM. The Auto Focus does not work. When I turn the camera on the letters MF flashes in the window on the back. The lens is set to AutoFocus and when I change it to ONE SHOOT or AL SERVO it flashes a message that says "Set the focus mode switch on the lens to AF" which it is already there. If I switch the lens to MF - it does not flash.

Are you using a Canon body? Those are some unusual messages. Sounds like you have a non-Canon body and a bad or wrong type of mount adapter, to me.

Re: EF 100-400 Auto Focus does not work.

ccobb66 — Fri, 30 Jul 2021 05:33:46 GMT

Thank you. Sent it off yesterday and I already miss it.

Re: EF 100-400 Auto Focus does not work.

Tonytech88 — Fri, 06 Dec 2024 02:54:44 GMT

I have a canon ef100-400 and it has an af that does not work. The af switch don’t work. So, I open the back where the ribbon cable from the af switch go and found out that ribbon that is supposed to stick on the side of the barrel delaminate and I stick it back using a very tiny amount of glue and everything works.