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EF100-400mm L IS II USM suddenly stopped focussing


I replaced my EF100-400mm first series lens with 2nd series a couple of years ago. I noticed over the last few weeks that focussing had become problematic with the lens failing to focus on the occasional subject (mostly birds among thickets of tangled branches). This seemed intermittent and I was hoping it was the branches that were causing the issue. But, suddenly, overnight the lens stopped focussing altogether, and that's when pointing at clearly defined, uncluttered subjects. I am an experienced photographer and know this isn't down to wrong settings etc. But what can be the cause? Are the motors on these lenses likely to fail after 2 years? The motor still drives the focussing but not every time, and it never achieves focus. After a couple of whirrs it gives up. If it's the motor, is it worth replacing? Anyone know the cost? (I'm in France, so a € price would help.)



Welcome to the forums!  Sorry you are experiencing issues with your gear.

I would like to ask a few basic questions to get a better understanding of your issue so that I can form a baseline on how to troubleshoot your issue.  Seeing how you are a highly experienced photographer, please do not be offended by the simplistic nature of some of the questions that myself or others might ask.  Thank-you, for your understanding and cooperation.

What camera body are you using with the lens?  Did you purchase a new lens from Canon or a Factory Authorized Dealer?  Was it used?

Do you have any filters installed?  If so, remove them.  This lens and UV,CPL filters do not seem to agree with one another.  I think it has something to do with the internal lens coatings.

"The right mouse button is your friend."

Hi Waddizzle. 

The lens was purchased new, more than 2 years ago so out of warranty. It is well looked after and has suffered no bumps or falls that I know of.

I have 5D MkII and 7D MkII bodies and the 100-400 no longer works with either body. It is usually left mounted on the 7D.

I tried removing the UV filter but this has made no difference. 

I can achieve perfect focusing on the manual setting, so everything internally appears to be still aligned.

Hope this helps.


Not applicable

Have you tried removing and reinstalling the lens to wipe the lens and camera contacts? Do you have another camera to try the lens on? Do other lenses work ok with your camera? Trying these suggestions will help narrow down the cause of your focusing issue.

Thanks Bob. Yes, I have tried all the obvious solutions. Other lenses work on my 7D body but the 100-400 lens does not work on my 5D body or 7D. I have carefully wiped the connections on lens and body. They look pristine so I assume this isn't the problem.

Not applicable

There is a firmware update for that lens, v1.07. It was to solve IS problems, but no mention of focusing problems. Just one other question, is the lens mount loose on the lens? As Waddizzle mentioned, some have reported issues with that lens and some filters. Do you have a filter on the lens?

Other than that, it would seem it needs to be sent to Canon for repair.

The lens attaches to the body very firmly. Removing the UV filter makes no difference.

Any idea as to the range of possible problems that Canon would be looking for? Does recalibration resolve issues like this or am I probably looking at a new motor? Any idea of costs? My 2x bodies are old and will need to be replaced at some point and I had considered mirrorless, so I'm reluctant to spend a fortune repairing a lens that may become obsolete, although at just over 2 years old it should have a long life ahead of it! My Series 1 100-400mm was still going strong when I changed it after nearly 20 years (and now my son-in-law uses it).

Not applicable

I just thought of something else to check, is the focus limiting switch in the correct position? I would try moving that switch and the AF/MF switch back and forth a few times to make sure that they are making contact. If that fails, I would suggest contacting Canon repair and getting an estimate. If you get it repaired and later get a mirrorless R series camera, you can use a Canon adaptor and continue to use the lens. I use that lens on DSLRs and I would get it repaired if it were mine. It is a fantastic lens.

Canon Repair Web Site 

Thanks again. I have moved the lens button back and forth from AF to MF, and the other from full to 3m-infinity with no effect.

When I take up the camera and depress the shutter button, it makes a one-off effort to focus  but quickly gives up, always stopping at one end or other of the focussing range (0.98 or infinity). It won't try to focus again until it has been left to rest for a few minutes or turned off and on again when it repeats this cycle. I don't know if that might be a further clue as to where the problem lies. 


Not applicable

In the camera's AF menu, look for setting of Lens drive when AF impossible and make sure it is set to ON.

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