Autofocus defect 4 times - Sigma art lenses on Canon R8

[Leanne16]

Hi,

I'm new here, I registrated so I could ask a question about my Canon R8 and my Sigma lenses. English is not my native language, but I hope you can still follow it.

I've been shooting with the R8 for a few years now. Initially, I used a simple kit lens and the Canon EF 50mm 1.8, both  I still had from my previous Canon (a basic SLR). To use the old lenses, I got a Canon EF-RF mount adapter. This worked fine, but I was lacking some sharpness, so I decided to buy some other lenses. These became the Sigma 50mm 1.4 ART and the Sigma 105mm 1.4 ART. I was very pleased with both, especially the 105mm.

Unfortunately, the 105mm's autofocus suddenly stopped working. I was shooting (indoors, no unusual conditions), but the lens couldn't find focus. It made chattering noises and kept searching for focus. Manual focus worked fine. I tried the lens on other bodies, but the autofocus didn't work there either. It was still under warranty, so I received a different 105mm. After a few months, the same problem reappeared, again "suddenly." The lens couldn't focus again and was making a tremendous amount of noise. Then I had the lens repaired at Sigma (that was in July 2025), and it's been working fine ever since. Sigma told me it was a "coincidence" that I had the exact same problem twice with two lenses.

But it got even weirder. One day, the 50mm lens also started making that noise, searching for focus for a long time. The autofocus continued to work a little, but I sent it in for repair anyway because the noises sounded very strange. I've had the lens back from repair for a month now, and last week the autofocus stopped working completely. It seems the motor is broken now; the autofocus doesn't do anything and doesn't make any noise. Manual focus is still working.

I find it very strange that I've already had this problem with the autofocus on a Sigma lens four times. Could there be a problem with my body, that it's essentially destroying the lenses? Unfortunately, I'm not technically savvy at all. I really enjoy taking great pictures and like it when everything just works, but I know very little about the internals of lenses and cameras.

Does anyone recognize this problem? And what would you recommend? Should I switch to Canon L lenses (I went for Sigma mainly for price reasons and because the sharpness is amazing). Or should I get a different body so I can keep using Sigma? I'm not sure. I do find it very daunting to photograph special moments; I really need more gear to keep on hand, in case the lenses fail.

Thanks for reading!

Sincerely,

Leanne

[Leanne16]

@march411,
What a kind offer, thank you very much! I live in the Netherlands, so I think it would be easier if I purchase a dock myself. (I only realized this was a USA forum after I had already posted my message; I thought it was a general Canon forum).

I received a message today that the lens from the camera shop has been sended to Sigma. They suspect a software problem. I expect they will update the lens there as well, but I am definitely going to purchase a dock myself. Thanks for your advice @shadowsports a.o.

@ LeeP

A chatterer; you mean that the lens made a lot of noise? Did the lens also have trouble finding focus?

@ ebiggs1
Glad that Sigma works well for you. Could the problem then lie in the operation of Sigma in combination with a Canon Ef-Rf mount adapter? Because LeeP also had a problem with Sigma and he used an adapter too? And I agree with you that there could be a lens in between that was old or dropped once by the previous owner. But with all three, that doesn't seem possible to me...

Anyway, I really want to purchase an extra lens anyway because the 50mm isn't back anytime soon. Do you have experience with the Canon RF 28-70mm F2.0 L? It has a very different price tag than Sigma; is it worth it, or do you recommend a different Sigma lens?

[LeeP]

"A chatterer; you mean that the lens made a lot of noise? Did the lens also have trouble finding focus?"

Yes.

Once the camera was turned on the Sigma lens would incessantly try to find focus and made a lot of noise as it hunted for the focus point. Some of it was exacerbated by light i.e. the dimmer it was the more "chatter" to find focus. 

My 28-135 IS Canon EF zoom on the same EF-to-RF converter didn't have that chatter response nor did the EF Tamron zoom I had. 

The Sigma lens also chattered on my Canon EF mount DSLRs and much as it did on my RF mount bodies with the adaptor.

I just chalked it up to a Sigma issue, but it always found focus.

As for "(I only realized this was a USA forum after I had already posted my message; I thought it was a general Canon forum)...", you will find that you a 100% welcome here and you will find people to be generally helpful.

[ebiggs1]

"Do you have experience with the Canon RF 28-70mm F2.0 L?"

A hundred time over, I recommend RF lenses for R series cameras. No matter how you spin it, no matter how little effect, you are still trying to convert or adapt a lens to do something it was not designed to do to do something else.

Although the Sigma dock isn't expensive, if you sent the lens to Sigma they will update it for you. You may never need the dock again. I have the Sigma dock and I have a dozen Sigma lenses. I bet I haven't used the dock more than six times; not a lot considering the dock has been out for around 15 years.  However, when you need it, you need it so there's that.

"...you mean that the lens made a lot of noise? Did the lens also have trouble finding focus?"

Causation and correlation my friend. You can't draw a definitive conclusion from what happened to a lens that another person has/had. You would need way more detailed infor. His lens was bad so my lens is bad is not a fact and is just not a rational thing to conclude.

[ebiggs1]

"...I thought it was a general Canon forum."

Well kido it really is a 'general' forum. We don't care where you are from if we can help. Ask any questions you want. 😊

It is owned and maintained by Canon but by far and away the members are just Canon consumers just like you. It's just some of us have been in the photography world and Canon users for, in my case many, decades. And in my case, personally, more than half a century!

[Waddizzle]

“ @ebbigs1, Most of the time I'm shooting with kids, outside. The shutter speed varies a lot but is actually always above 1/250, aperture between 1.8 and 5.6. ISO as low as possible, usually between 100 and 800. I always hold the camera with both hands outstretched, the strap around my neck. I don't know what might affect the operation of the lens? “

I had the same questions about your camera settings and shooting conditions. Except, you are having focus issues and provided details about your exposure settings. Questions remain about your shooting mode, drive mode, and your AF settings.

The advice to reset the camera was a good idea.  But did you test the camera before you began changing the camera settings?  

I suggest testing the camera in Intelligent Auto shooting mode.  That’s the green [A+] setting on the shooting mode dial. This puts most of AF settings and other settings into a known state.  It also takes any custom settings that you might be using off the table.