topic Re: Help with R8 Focusing Issues in EOS DSLR & Mirrorless Cameras

Help with R8 Focusing Issues

SumanV — Tue, 09 Sep 2025 15:30:34 GMT

Hi, I recently bought an R8 from a photographer and I need help in understanding the camera and any user/device issues. I come from an RP and still have it. My main problems are in using the R8 with EF 400mm f5.6L and that is the only lens I have used with the camera

I focused on the moon during the lunar eclipse and got the blue confirmation. After some time, the box became red and the lens refused to focus (box was on the moon all the time). Also, it did not make any attempt to focus. I restarted the camera, but the issue persisted until magically it started to focus again. I had issues like this before where the AF completely stops for some time and becomes active again. At that time, I didn't think much of it but my latest experience prompted me to ask for help. (I'll be visiting the Canon service center later this week)

At the time I was having focus issues, I also tried to manually focus by setting the switch on the lens to MF. I moved the focus ring, but the lens simply did not respond. The distance scale did not change. It was as though the lens died on me. After some time, the distance scale moved! I also noticed that the lens was behaving erratically with the distance scale not showing any movement for a few times.

When the lens was in MF mode, the focus aid box appeared. The confirmation from the aid was also erratic. It showed confirmation a few times and a gray box at other times. All this time, the subject was in focus, and I did not move the focus ring!

I got the camera sensor cleaned and the lens also cleaned at the service center a few weeks before.

Is there a problem with my R8 and/or lens? I'd appreciate any tips/advice from experienced members regarding these issues. I have other issues with getting sharp pictures for birds in flight, image quality and understanding the AF system but I'll ask these after this issue gets resolved.

Thanks,

Suman

Re: Help with R8 Focusing Issues

wq9nsc — Tue, 09 Sep 2025 15:53:15 GMT

If you can get the lens to NOT respond again to its manual focusing ring, turn the camera off and remove the lens from the camera body carefully (so as not to shake it) and see if the manual focus ring on the lens now works. If not, the problem is definitely in the lens because the focus ring will drive the lens focusing assembly even when no power is applied since it isn't a "focus by wire" model.

There is a note in the manual for this family of lenses that if you autofocus outside of the range set by the focus range limit switch then the lens may stop focusing at the start of the focus range. But if this is what happened, releasing and then doing another half press of the shutter button should cause it to focus.

I really like this lens and shot a lot of daytime sports with it for years. It focuses rapidly and produces high quality images and is a pretty simple and reliable lens. But if it has quit responding to input from the manual focus ring when no power is applied then there has been a mechanical failure inside. It seems to have some sort of slip clutch mechanism if movement is attempted beyond the end of the range and intermittent failure of this could be the issue.

Rodger

Re: Help with R8 Focusing Issues

deebatman316 — Tue, 09 Sep 2025 16:10:30 GMT

Hi Rodger, I was also thinking the setting “Lens Drive when AF is Impossible” was set to disable. If it is the camera will refuse to refocus. I would like to confirm that the lens name that the OP stated was correct. Canon did make other 400mm lenses that are focus-by-wire. I’m also wondering did the OP turn the focus ring to the end of the focus throw. If they do the scale doesn’t move. But did they turn it the other way though. You can feel the clutch as you turn. I would also check the setting called “Preview AF/ Continuous AF” that will cause the lens to focus constantly.

Re: Help with R8 Focusing Issues

SumanV — Tue, 09 Sep 2025 16:39:53 GMT

@wq9nsc wrote:
If you can get the lens to NOT respond again to its manual focusing ring, turn the camera off and remove the lens from the camera body carefully (so as not to shake it) and see if the manual focus ring on the lens now works. If not, the problem is definitely in the lens because the focus ring will drive the lens focusing assembly even when no power is applied since it isn't a "focus by wire" model.
There is a note in the manual for this family of lenses that if you autofocus outside of the range set by the focus range limit switch then the lens may stop focusing at the start of the focus range. But if this is what happened, releasing and then doing another half press of the shutter button should cause it to focus.

I really like this lens and shot a lot of daytime sports with it for years. It focuses rapidly and produces high quality images and is a pretty simple and reliable lens. But if it has quit responding to input from the manual focus ring when no power is applied then there has been a mechanical failure inside. It seems to have some sort of slip clutch mechanism if movement is attempted beyond the end of the range and intermittent failure of this could be the issue.
Rodger

Hi Rodger! Thanks for the reply. A lot of the information that you gave is new to me and I am grateful for that. I do not remember if I switched off the camera before turning the focusing ring manually, but I certainly did not remove the lens from the body. I'm curious to know why the lens should be unmounted.

Strangely enough, like voodoo magic, the lens started to autofocus and after some time responded to manual focusing! However, I noticed that the distance indicator got stuck on some occasions. I think it must be a lens issue.

I too bought the lens as its sharp, but I did not have enough success with the R8. I tried BIF but only a few shots were acceptably sharp. It could be due to a user error as my hands usually get wobbly holding this lens and the R8 after some time.

"There is a note in the manual for this family of lenses that if you autofocus outside of the range set by the focus range limit switch then the lens may stop focusing at the start of the focus range." I'm curious to know in what situations this happens. I was focusing on the moon which is typically at infinity. So, this should definitely be within the limit.

Re: Help with R8 Focusing Issues

SumanV — Tue, 09 Sep 2025 16:35:25 GMT

Hi, Demetrius. That's an interesting point. I'd need to check and confirm. I moved the focus ring either way but did not get a response.

Re: Help with R8 Focusing Issues

SumanV — Tue, 09 Sep 2025 16:37:42 GMT

I do not know if this is relevant or important, but the issue started when I moved the focus box to one edge of the screen.

Suman

Re: Help with R8 Focusing Issues

ClimbingBolted — Tue, 09 Sep 2025 18:48:47 GMT

@SumanV wrote:

Hi, I recently bought an R8 from a photographer and I need help in understanding the camera and any user/device issues. I come from an RP and still have it. My main problems are in using the R8 with EF 400mm f5.6L and that is the only lens I have used with the camera

I focused on the moon during the lunar eclipse and got the blue confirmation. After some time, the box became red and the lens refused to focus (box was on the moon all the time). Also, it did not make any attempt to focus. I restarted the camera, but the issue persisted until magically it started to focus again. I had issues like this before where the AF completely stops for some time and becomes active again. At that time, I didn't think much of it but my latest experience prompted me to ask for help. (I'll be visiting the Canon service center later this week)

At the time I was having focus issues, I also tried to manually focus by setting the switch on the lens to MF. I moved the focus ring, but the lens simply did not respond. The distance scale did not change. It was as though the lens died on me. After some time, the distance scale moved! I also noticed that the lens was behaving erratically with the distance scale not showing any movement for a few times.

When the lens was in MF mode, the focus aid box appeared. The confirmation from the aid was also erratic. It showed confirmation a few times and a gray box at other times. All this time, the subject was in focus, and I did not move the focus ring!

I got the camera sensor cleaned and the lens also cleaned at the service center a few weeks before.

Is there a problem with my R8 and/or lens? I'd appreciate any tips/advice from experienced members regarding these issues. I have other issues with getting sharp pictures for birds in flight, image quality and understanding the AF system but I'll ask these after this issue gets resolved.

Thanks,

Suman

Glad to hear it started working again, even if it felt like pure voodoo magic 😅. From what you describe, it definitely sounds more like a lens quirk than a body issue, especially with the distance indicator sticking sometimes. The note in the manual about the focus range limit can be confusing — basically, if the AF is trying to lock outside of the range you’ve set, it can ‘stall’ at the start until you bring it back into range. In practice, it happens more when switching quickly between close and far subjects. For the moon (at infinity), you should’ve been well within range, so I’d lean toward the lens itself acting up. And yeah, handholding that lens with the R8 can get tough after a while — even a slight wobble shows up when you’re shooting BIF or the moon. A monopod or just extra stabilization might help a lot.

Re: Help with R8 Focusing Issues

wq9nsc — Tue, 09 Sep 2025 18:45:06 GMT

Hi Suman,
I suggested unmounting the lens because I have never tested to see what happens when the camera is trying to drive the focusing system at the same time you are trying to use the manual focus ring. IF there was a camera malfunction that caused this, then you could run into the situation where the camera is trying to control the focus system even with the power switch turned off because on modern camera bodies the switch doesn't actually interrupt the power but instead tells the controller to power down the camera. Thus a controller issue would result in potential issues even with the power switch turned off.

So I wanted to ensure that the problem is still present when the lens is removed from any source of power/control.

With the lens focusing but the distance indicator getting out of sync/sticking then it definitely sounds like an issue in the lens. Probably the distance indicator is getting hung up at times and preventing the rest of the focus mechanism from traveling freely. I doubt if Canon services this lens anymore but I am sure you could find a third party shop to look at it. It could have a bit of "wear material" has come loose and is jamming the mechanism at times so it is possible a good internal cleaning would clear the fault but it would require a shop to disassemble the lens for cleaning.

The EF 400 f5.6 is a very utilitarian lens, nothing fancy like IS or a very wide aperture, but it does it job very well. The integrated lens hood is a nice feature and it is the only Canon lens I own built that way. Mine went hiking a lot with my original Canon 1D Mark II body because it provides a nice combination of sharp optics, fast focusing, and reasonable size/weight. I hope that you can have your lens repaired and put back into service.

I have never run into the behavior described in that note in the manual and I used the focus limiter quite often shooting soccer because I wasn't using the lens for players who were close. The wording in that note in the manual is a bit awkward and my best guess is that behavior might occur when the lens is set to focus on something close and then the limit switch is set so that close focus setting is no longer within the valid range. So it fails on the first half shutter push since it is out of the limited range and then the second half push causes it to go into action. Canon states it isn't a fault but it certainly sounds like a design/firmware glitch to me.

I own several lenses including the EF 200-400 f4 with built in 1.4X switchable extender and there is a huge list of exceptions/precautions in the manual about when the extender switch can be operated based upon the camera model and it sounds like many operations will result in an error. I have used this lens a lot for sports and often switch back and forth rapidly during a sequence and I am sure that it happened more than once while I had the AF system tracking the play. I have never gotten an error and that is probably because I have only used it with 1DX II and III bodies but there is a confusing list of prohibited/problematic operations. So the documentation isn't always clear.

Rodger

Re: Help with R8 Focusing Issues

jrhoffman75 — Wed, 10 Sep 2025 12:06:47 GMT

@SumanV wrote:

Hi, I recently bought an R8 from a photographer and I need help in understanding the camera and any user/device issues. I come from an RP and still have it. My main problems are in using the R8 with EF 400mm f5.6L and that is the only lens I have used with the camera

I focused on the moon during the lunar eclipse and got the blue confirmation. After some time, the box became red and the lens refused to focus (box was on the moon all the time). Also, it did not make any attempt to focus. I restarted the camera, but the issue persisted until magically it started to focus again. I had issues like this before where the AF completely stops for some time and becomes active again. At that time, I didn't think much of it but my latest experience prompted me to ask for help. (I'll be visiting the Canon service center later this week)

At the time I was having focus issues, I also tried to manually focus by setting the switch on the lens to MF. I moved the focus ring, but the lens simply did not respond. The distance scale did not change. It was as though the lens died on me. After some time, the distance scale moved! I also noticed that the lens was behaving erratically with the distance scale not showing any movement for a few times.

When the lens was in MF mode, the focus aid box appeared. The confirmation from the aid was also erratic. It showed confirmation a few times and a gray box at other times. All this time, the subject was in focus, and I did not move the focus ring!

I got the camera sensor cleaned and the lens also cleaned at the service center a few weeks before.

Is there a problem with my R8 and/or lens? I'd appreciate any tips/advice from experienced members regarding these issues. I have other issues with getting sharp pictures for birds in flight, image quality and understanding the AF system but I'll ask these after this issue gets resolved.

Thanks,

Suman

If I'm not mistaken blue focus box is Servo mode and green would be One Shot. Not sure Servo would be the correct mode for a moon shot since Servo doesn't lock focus.

Re: Help with R8 Focusing Issues

SumanV — Wed, 10 Sep 2025 18:23:06 GMT

Hi John. Yes, I agree with you. However, I was talking about the focus guide in MF mode. The box turning green is a sing of focus confirmation, if I understand its operation correctly. I was able to autofocus on the moon in servo mode and I have done it with my RP as well. I am not sure why you say that servo would not be the correct mode. Doesn't the blue box imply that focus is achieved?

Regards

Suman

Re: Help with R8 Focusing Issues

SumanV — Wed, 10 Sep 2025 18:32:54 GMT

Thanks again, Rodger. You have made a lot of interesting points which are new to me. In my case, when the AF issue was happening, I turned the switch on the lens to MF mode. Would the camera still control the lens at this point? I think it should not, but I do not know.

The canon execs warned me that they would stop supporting the lens in the near future when I visited them a month back. I hope that they would check the lens and repair it if needed. Going to a third party service provider would be my last option.

Regards

Suman

Re: Help with R8 Focusing Issues

SumanV — Wed, 10 Sep 2025 18:36:52 GMT

Thanks for the tip about the monopod. I'm still new to the R8 and there are some quirks I need to understand to efficiently use the camera. My major worry is that I should not have a defective R8 especially because I bought it second hand!

Regards

Suman

Re: Help with R8 Focusing Issues

SumanV — Sat, 13 Sep 2025 17:25:44 GMT

A small update regarding the issue.

1) Preview AF was turned off

2) Lens drive when AF impossible was set to enable i.e. it will still try to achieve focus

I visited the service center and told them of the issues I had. The exec suspected it to be a lens issue and stated that the older lens may not be optimized for the newer mirrorless bodies. He suggested to use RF lens, and he was confident that it will perform much better. I decided to hold off on the inspection and repair for now.

I am still not happy with the sharpness. I might be expecting too much. I will post some images for feedback.

Re: Help with R8 Focusing Issues

Waddizzle — Sat, 13 Sep 2025 19:19:26 GMT

“ I do not know if this is relevant or important, but the issue started when I moved the focus box to one edge of the screen. “

This is very important. The AF system will try to focus where the zag point is located.