topic Re: EF lens autofocus stopped working with R7 but works with T3i in EOS DSLR & Mirrorless Cameras

EF lens autofocus stopped working with R7 but works with T3i

captinsane — Thu, 19 Mar 2026 17:36:21 GMT

I have an R7, maybe 1.5 years old, with the cheaper of the two Canon EF-RF adapters. I have a 300mm f4/L that stopped autofocusing on the R7. I was out birding; everything worked as expected for a while until it didn't. I never removed the lens, but kept the camera off while not using it to conserve battery. I carry the camera on a BlackRapid R strap with the tripod nut connected to the tripod foot on the lens. I bought the lens used around 2014 and while it's mostly worked fine, the manual focus hasn't worked in probably 3-4 years, if not longer.

So far, I've tried

300mm on my T3i: works as it should
EF nifty fifty with the adapter on the R7: works as it should
RF 18-150 on the R7: works as it should
Cleaned contacts with microfiber towel on all contacts for the adapter and 300mm (I also frequently use a mk1 1.4x teleconverter and have been testing without that, but cleaned the contacts as well)

Best I can tell, the camera firmware is up-to-date. I uploaded some photos after the lens stopped working using the EOS Utility, and it didn't mention the camera needing a firmware update. Also, I've seen on google people saying to clean the contacts with isopropyl alcohol, but in Canon's documentation that came up in a google search, it only mentioned a microfiber cloth, which is why I haven't tried the ISO yet

Re: EF lens autofocus stopped working with R7 but works with T3i

deebatman316 — Thu, 19 Mar 2026 18:06:54 GMT

Hi @captinsane Please confirm which EF 300mm lens you own. Canon has made 2 F/4 versions of that lens. One had IS and the other did not feature. A metal plate is affixed to the lens with the complete name on it. The focus ring on that lens should always work. The focus ring is mechanically connected to the focusing elements. This is NOT a focus-by-wire. There’s a clutch under the focus ring so you can safely turn the focus ring while the lens is set to AF Mode. Does the EOS R7 even recognize that lens? Does it report an aperture value? Have you checked the AF/ MF switch on the lens? That switch takes priority over the switch on the camera. That switch on the body only applies to RF/ RF-S lenses without their own AF/ MF switch on them. Does the camera report MF or does it report an AF mode like One Shot? Have you tried the lens on a different R Series cameras? Older lenses with failing components may work fine on an older DSLR. But once mounted to an R Series camera problems arise due to faster communication speeds. That weren’t possible with DSLR cameras especially older ones that were slower to begin with like a Digital Rebel. Is this the OEM Canon brand adapter. Or a 3rd Party adapter. 3rd Party Mount adapters are nothing but trouble.

Re: EF lens autofocus stopped working with R7 but works with T3i

captinsane — Thu, 19 Mar 2026 18:25:44 GMT

Hi, thanks for your quick reply. It's the 300mm with IS. The focus ring doesn't work anymore 99% of the time so I'm not sure what's up with that.

The R7 recognizes it, gives aperture values, and will even set the ISO (camera is on auto-ISO). I've tried turning on/off the AF/MF switch o the lens and futzed with the one on the body as well. I don't see whether it's telling me MF or AF, but when I half-press the shutter button, the focus box turns red from white. I tried a few different AF modes with the same result. I also tried things with the focus distance switch, same thing, and tried focusing on things close and far in both modes. I don't have another R camera or easy access to one, shorting of rending, to test it on. The adapter is the Canon OEM one, the more basic of the two.

Re: EF lens autofocus stopped working with R7 but works with T3i

deebatman316 — Thu, 19 Mar 2026 18:37:56 GMT

@captinsane Did you try turning the focus ring both ways? The focus distance scale should move. The focus ring doesn’t work if the camera is driving the AF motor. So I would unmount the lens and turn the focus ring both ways and see if the focus ring works. The focus ring will turn indefinitely without any hard stops this is normal. I would also check the setting called “Preview AF”. I would set this to DISABLE its a drain on the battery. The camera will show an AF operation when set to AF. The camera will show MF if the lens is set to MF. The camera sets the ISO the lens doesn’t set that. The only control over the lens is the Aperture from the camera. Will it AF on another camera though. Since it’s an older lens not every feature the EOS R7 has is compatible with it.

Re: EF lens autofocus stopped working with R7 but works with T3i

captinsane — Thu, 19 Mar 2026 21:30:18 GMT

I checked the focus ring with the lens off the camera. The focus distance scale does not move. I disabled Preview AF. I can change the aperture: I set the camera to Av and was able to change aperture using the wheel by the shutter button. I double checked the lens on my T3i: it autofocuses and lets me adjust the aperture

Re: EF lens autofocus stopped working with R7 but works with T3i

stevet1 — Thu, 19 Mar 2026 23:41:32 GMT

captinsane,

Based on the process of elimination that you outlined, it sounds to me like there is a "failure to communicate" between your adapter and the 300mm lens.

If the 50mm works with the adapter, the you know it's not the adapters fault.

And if your other lenses are working both with and without the adapter, you know it's not the camera's fault.

Steve Thomas

Re: EF lens autofocus stopped working with R7 but works with T3i

captinsane — Fri, 20 Mar 2026 01:41:04 GMT

Is that something Cabin or authorized repairer can fix or is it a lost cause? I've never needed camera gear fixed so I don't know how to go about it

Re: EF lens autofocus stopped working with R7 but works with T3i

stevet1 — Fri, 20 Mar 2026 02:39:17 GMT

captinsane,

That's a tough call. I myself don't have any experience with Canon repairs, but others in the Forum do.

My hunch is that if you bought the lens used in 2014, it's probably not going to be serviced by Canon.

You can buy used copies of this lens on ebay for between $300 and $500.

You would probably spend close to that on repairs, no matter where you go.

Newer versions of this lens with image stabilization run about $1,200.

I personally would just use it on my T3i, and save my money for a newer lens to use on my R7.

But, that's just me.

Steve Thomas

Re: EF lens autofocus stopped working with R7 but works with T3i

deebatman316 — Fri, 20 Mar 2026 02:56:10 GMT

@stevet1 that lens has IS. What I’ve noticed with older lenses with aging hardware, is that they work perfectly fine on an older camera. But once paired with a newer DSLR or adapted to the EOS R series. Communications error codes pop up. This is because Canon increased the communication speed between the lens and body.

Re: EF lens autofocus stopped working with R7 but works with T3i

stevet1 — Fri, 20 Mar 2026 05:20:20 GMT

Demetrius,

Thanks for letting me know. I have a lot to learn.

Steve Thomas

Re: EF lens autofocus stopped working with R7 but works with T3i

captinsane — Fri, 20 Mar 2026 12:03:22 GMT

It sounds like maybe it just stopped communicating with the camera. I guess I could find a Canon support email address to ask them

Re: EF lens autofocus stopped working with R7 but works with T3i

captinsane — Fri, 20 Mar 2026 12:52:20 GMT

Is there a way to get the attention of Canon for this post?

Re: EF lens autofocus stopped working with R7 but works with T3i

Danny — Fri, 20 Mar 2026 13:13:00 GMT

Hi, captinsane! If you'd like our own support technicians to weigh in on this, we recommend getting in touch with them directly. You can reach them Monday through Friday at 1-800-OK-CANON (1-800-652-2666). They can troubleshoot the issue with you and figure out a solution from there, and if that includes sending in your camera for repair, they'll walk you through that process, too.

We look forward to your call!

Re: EF lens autofocus stopped working with R7 but works with T3i

captinsane — Fri, 20 Mar 2026 13:11:54 GMT

Great, I will give them a call. Thanks! I was trying to figure out how to do it online, but I don't have my receipt anymore because I bought the lens 12 years ago

Re: EF lens autofocus stopped working with R7 but works with T3i

deebatman316 — Fri, 20 Mar 2026 13:32:58 GMT

Good morning @Danny thanks for stepping in while I was out.

Re: EF lens autofocus stopped working with R7 but works with T3i

ebiggs1 — Fri, 20 Mar 2026 14:30:58 GMT

"I bought the lens 12 years ago"

Don't be surprised it Canon no longer repairs that lens. If they do check to see how much a used copy of the lens in good working order is. It mat be cheaper to buy a different lens than to repair yours if possible.

Re: EF lens autofocus stopped working with R7 but works with T3i

captinsane — Fri, 20 Mar 2026 14:32:53 GMT

Thanks for the heads up. I called them and they said they do repair it, but quoted me between $230-700+ after I shipped it to them. I couldn't talk with someone who could narrow it down

Re: EF lens autofocus stopped working with R7 but works with T3i

Danny — Fri, 20 Mar 2026 14:37:14 GMT

Thanks for giving our support team a call! Until our Factory Service Center technicians can get your lens in their hands, a ballpark repair cost range will be the best we can provide at the moment. Once our techs have had a chance to look at it, they'll email you a free estimate and you can decide what you want to do from there.

Hope to get your gear working again real soon!

Re: EF lens autofocus stopped working with R7 but works with T3i

captinsane — Fri, 20 Mar 2026 15:18:42 GMT

Thanks. I understand it's hard to give a price without seeing it

Re: EF lens autofocus stopped working with R7 but works with T3i

ebiggs1 — Sat, 21 Mar 2026 14:19:28 GMT

"Good morning @Danny thanks for stepping in while I was out."

What an odd post was he expecting you to return?