EF 100-400 IS II dust gasket detached

[dqosja]

CleanShot 2026-08-22 at [email protected]IMG_7242.jpeg

Hi everyone, I’d like to ask for some advice about my Canon EF 100-400mm f/4.5-5.6L IS II USM.

A colleague of mine was using the lens recently, and I suspect that he may have tried to operate the zoom several times while the zoom tension ring was set very tight or possibly close to the “TIGHT” position.

Afterwards, I noticed that a thin strip of grey rubber/foam-like material had come out from the gap around the extending barrel and was being dragged along the outside of the lens.

I found a teardown video of the 100-400 II where what appears to be a similar grey sealing material can clearly be seen inside the lens, so I’ve attached:

• a photo of my lens showing the material that has come out;
• a screenshot from the teardown showing what looks like the same material in its original position.

Does anyone know exactly what this material is?

Could using the zoom while the tension ring is too tight cause this seal/material to come out or become damaged?

Most importantly, how significant is this issue? Is it mainly related to dust/weather sealing, or could it affect the zoom mechanism or other internal components as well?

Would you recommend sending the lens to Canon for repair, or is this something that can safely be left as it is if the zoom, autofocus and image stabilization are still working normally?

Thanks in advance for any advice.

[ebiggs1]

"Would you recommend sending the lens to Canon for repair,..."

Yes. 1 (800) 652-2666

[shadowsports]

Greetings, 

I agree with @ebiggs1. This is not an endeavor you want to attempt on your own.  Send it to Canon.  Yes it's going to cost some money. 

They will perform a full inspection, cleaning and repair the gasket.  Without this seal, the lens is more susceptible to dust and moisture.  We all know these types of environmental factors find a way in.  Without it, it becomes a lens that you won't use when it's dusty, or when moisture is present.  This is not practical.  

The tension ring uses a mechanical clamping force on the lens barrel and doesn't have any effect on the seal.  The seal on your lens failed because it's 12 years old.  These things have a usable life.  It's had many years of reliable use and has finally seen its end.  

[pzphotomama]

Definitely reach out to Canon to see if can be repaired!