Focus Issue RF 100-300 f/2.8 USM

[rgl47]

I've had the captioned lens for about 14 months now and it has worked great until about 2 months ago when a focus issue started when the lens is zoomed all the way out to 300mm or 420mm with the 1.4 TC.

I purchased the lens brand new from a camera shop and it has never been dropped or hit in any manner. When I zoom the lens all the way out to 300mm, or with the 1.4 TC on, 420mm, the autofocus continues to hunt and it never achieves focus. If I move the zoom just a hair lower under 300 or 420, it then works fine…as it normally did for months. I mostly use this lens with the R1 but I have tried it with my R3 and my R5ii and the issue persists with those lenses as well. I have also taken the 1.4 TC off and tried it and the issue persists. I spoke to the shop where I bought it and they basically said tough luck, it’s out of warranty. They said they would check with the Canon rep for a possible solution but that was 2 months ago and I have not heard anything. I have reviewed all my settings and there isn’t anything I changed since buying this lens brand new. I’ve always used lens drive when autofocus impossible "on" and it worked fine. I turned that off and issue persists. I did do an update to my camera bodies a couple weeks before I started noticing the issue, coincidence? I also cleaned all the contacts on both the lens and the bodies. I saw this morning there are camera updates for the R1, R3, and R5ii so I am going to update those today. The last update to the lens was February 2025 and I did do that update back then but I am going to redo the update just to make sure. There was a post from February 2023 wherein a user mentioned the same exact issue but that was with a RF 100-400 lens. What helped him was turning off lens drive when autofocus impossible. I don't think, and some other members agreed and noted in that post, that that should matter. Any help would be appreciated before I send this lens into Canon.

Regards,

Rob

[rgl47]

rs-eos,

I came across this post while searching for focusing issues with the new RF 100-300 f/2.8 USM. I have had this lens for just a little over a year and it worked great until about 2 months ago. I read your points above, specifically, “If you adjust the zoom just a bit less than 400mm, does it work then.” I was wondering why you ask this as your answer may help in my situation.

Just recently, after an update (coincidence?), when I zoom the lens all the way out to 300mm, or with the 1.4 TC on, 420mm, the autofocus continues to hunt and it never achieves focus. If I move the zoom just a hair lower under 300 or 420, it then works fine…as it normally did for the first 14 or so months. I mostly use this lens with the R1 but I have tried it with the R3 and the R5ii and the issue persists with those lenses. I have also taken the 1.4 TC off and tried it and the issue persists. I spoke to the store where I bought it and they basically said tough luck, it’s out of warranty. They said they would check with the Canon rep for a possible solution but that was 2 months ago and I have not heard anything. I have reviewed all my settings and there isn’t anything I changed since buying this lens brand new. I’ve always used lens drive when autofocus impossible on and it worked fine. I turned that off and issue persists. Any thoughts?

[ebiggs1]

"I also cleaned all the contacts on both the lens and the bodies."

As you have seen cleaning the contacts rarely to never helps and can be damaging to the contacts if done incorrectly. Also, updating the FW is not likely to fix your problem either unless the FW specifically addresses the 100-400mm lens. You need to send the lens back to Canon for a C&C and when you do make sure you tell them it has this problem. Call Canon 1 (800) 652-2666 or you can do it on-line where you registered your lens with Canon USA.

[normadel]

Are you using the Canon RF 1.4x Extender/teleconverter? Anything else would be suspect.

Download the lens manual. Discusses Extenders.

https://gdlp01.c-wss.com/gds/8/0300047238/01/rf100-300f28-lisusm-im-eng.pdf

[Hazel_T]

Hi rgl47,

I'm sorry to hear you're having focus issues with your lens when it is zoomed all the way out. The Lens Drive when Autofocus Impossible would technical keep the lens from hunting for focus, but it could also prevent it from focusing. Disabling that is more useful when your subject is always at a set distance from the camera. When that is disabled if the subject isn't immediately detected the camera doesn't hunt for focus. If your subjects are at different distances it is best to leave Lens Drive when Autofocus Impossible On. With it on if the camera is unable to immediately detect your subject it will check through the full focal range to try and detect it.

Looking at your message you already tried some of the trouble shooting we would recommend. One thing to double check would be to attach the lens on your EOS R5 Mark II, take the camera out at mid day when the sun is at its brightest, put the camera into Auto mode, and check to see if the same thing is happening. That can help determine if this is related to something like settings or light conditions. In auto mode the camera should be trying to pick optimal settings for the conditions and at mid day there should be plenty of light for the camera to focus.

If the issue is happening in Automatic then the other thing to check is related to filters on the lens. Sometimes if filters are on the lens they can alter the focus enough that the camera is unable to confirm it. With the filter off try taking another photo. You should check this even if you just have a clear protective filter on it.

If the lens is the only lens with the issue we would recommend sending it in to the factory service center for repair. If the issue is with every lens on the camera body we would recommend sending the camera body in to the factory service center for repair.

The Canon U.S.A., Inc. online repair portal allows you to set up service in a few simple steps. The repair portal gives you the ability to set up service for multiple pieces of equipment at once, and to receive a repair estimate in the majority of cases, depending on your model and issue. The portal also allows you to upload images or videos that will assist us in repairing your product. You can also select how you wish to be notified of the progress of your repair. The portal's service history section allows you to view all services that have been performed on any of your camera or video products since January 7, 2020. 

Please follow the link below to access our online repair portal to arrange for service:

https://mycanon.usa.canon.com/signin

Instructions for Accessing and Using the Online Repair Portal

You will need to access or create your My Canon Account.

If you already have a My Canon Account and your product is already registered, simply click on the “Get Repair Services” link on the left menu and follow the onscreen instructions to arrange for service for your product.

If you have a My Canon Account and your product is not registered, you must register your product first. Click on the “Get Repair Services” link on the left menu, then click on the “Register Product” link on the right. After your product is registered, click on the “Get Repair Service” link on the left menu and follow the onscreen instructions to arrange for service for your product.

If you do not have a My Canon Account, you will need to create one. After you create your account, click on the “Add Product” link to register your first product. After your product is registered, click on the “Get Repair Service” link on the left menu and follow the onscreen instructions to arrange for service for your product. 

Once you have completed the repair request, you will have an opportunity to print a copy of the request for your records. This request form will also contain shipping instructions and an address label that you will attach to the outside of your shipping box when mailing your equipment for repair.

[rgl47]

Hi normadel,

Yes, I am using the a new/latest Canon RF 1.4x extender. The issue does happen with or without the extender on the lens. And, I do not use any filters on the lens.

[rgl47]

Hi Hazel_T

Thank you very much for your reply and info.

I'm going to try disabling lens drive when autofocus impossible and do some checking. In the past, when I had it disabled, it still did the same exact hunting as it was doing when on. And, the thing is that what it's doing never happened until about two months ago. The issue is also intermittent and it seems if I turn the camera off, take the battery out and then use it, it's good for a period of time before it starts doing it again. I've just been trying to exhaust every option before sending it to Canon.

I do not use any filters with the lens and the extender is a Canon RF 1.4x TC. With or without the TC, the issue happens.

I will try the lens on the R5ii in auto and in bright light and see what happens. I am out of town right now and do not have there R5ii with me so as soon as I can try your option, I will and report back.

I am finding it hard to believe that such a great quality lens for the first 12-14 months all of a sudden went bad but and I am hoping it's just a setting or ? but thanks for all the repair portal info...hoping I don't have to send it in but..

[ebiggs1]

Sorry for the typo above, "FW is not likely to fix your problem either unless the FW specifically addresses the 100-400mm 300mm lens."

But if I had the Canon RF 100-300mm f/2.8 L IS USM Lens, I would not mess with it for a second instead send it to Canon and let them check it out.

"The issue is also intermittent ..." and exactly why you doing any testing on a nice sunny day will only be for your enjoyment of a walk outside on a nice sunny day. It will confirm nothing. This is not your run of the mill kit lens, my friend.

[rgl47]

Thank you, ebiggs1. It's a phenomenal lens when it works right...and it should be when it's that much money. Offline, I have been told Canon CC will just say it's user error or that the lens is working normal on their end...and they will send it back. I'm just not too confident Canon CC will mend the issue. I remember the days when many of the camera/lens manufacturers gave a 3 year warranty because they knew they made quality. It's different these days and it's something this issue started just after a year. Does anyone know how much Canon CC would charge me diagnosis of the issue?