topic RF 24-105 f/4 L - Dust inside rear element? in EF & RF Lenses

RF 24-105 f/4 L - Dust inside rear element?

gnartS — Sun, 22 Mar 2026 07:06:19 GMT

Will canon actually clean dust/"things" inside the rear lens element that is absolutely affective image quality.

Looking inside my lens i can see a white blob (almost like fibre) towards the outside and a further smear of maybe dust towards the centre.

It shows clearly on blue skies as a large instinct dark circle at f/10 on my R6 and a very very obvious blob(s) at f/16 and narrower.

Im certain its not sensor dust:-

- The blob changes size as the lens is zoomed

- The blobs still exist but in a slightly different position when used on my crop R7. Its gone on my R6 zoomed in past about 40mm (its on the top middle edge).

- My 100-400 is clean taking the same test shots.

Lens is about 5 years old, bought new. Its been there at least a year.

My RF 16/2.8 has similar but nowhere near as bad issue.

What are the options here ? The lens is far too expensive to dump but its also only about half usable now unless i zoom in or make sure theres no sky in a shot. Yes i could edit every image but video its even harder.

R6, 24mm f/22. Right hand, top and centre blobR7, 24mm (so 40ish). Centre visible, right visible. Top cropped off with APS-C

Re: RF 24-105 f/4 L - Dust inside rear element?

shadowsports — Sun, 22 Mar 2026 09:02:08 GMT

Greeting,

Yes, Canon will clean your lens. Start by registering the lens in your MyCanon account. Then initiate the cleaning/maintenance service in the portal. It includes a multi-point inspection for your product.

You may want to take a look at your sensor too, to make sure that it's not dirty before sending in your lens.

https://myprofile.americas.canon.com/us/signin

Re: RF 24-105 f/4 L - Dust inside rear element?

gnartS — Sun, 22 Mar 2026 09:12:51 GMT

Lens is registered (and repaired by them previously about 3 years ago with a front element scratch that was visible).

Sensor is fine- i check and wet clean it myself when needed. Lens is showing the blobs on 2 bodies (one of which is 3 days old only) and is causing issues.

Re: RF 24-105 f/4 L - Dust inside rear element?

ebiggs1 — Sun, 22 Mar 2026 14:33:54 GMT

"Will canon actually clean dust/"things" inside the rear lens element that is absolutely affective image quality."

You need to ask for a C&C. But be warned if that "blob" is fungus Canon will most likely not clean it or even touch it.

Good lord you have a lot of mess inside your lens. I would strongly suggest you change your shooting habits or storage habits completely. 😲

Re: RF 24-105 f/4 L - Dust inside rear element?

gnartS — Sun, 22 Mar 2026 14:37:43 GMT

Not a lot i can change when its used for shooting in temperature and tropical climates on a daily basis. First lens ive ever seen with this issue in 25 or so years of using Canon lenses.

Expected L to be more resistant (my 100-400 is fine though, as are various non Ls)

Re: RF 24-105 f/4 L - Dust inside rear element?

Stephen — Sun, 22 Mar 2026 18:08:27 GMT

A clean and check does *not* include taking apart the lens to clean the individual elements. You can find everything that is included in the different types of maintenance service options at https://canon.us/CMS

When you request the cleaning, be sure to document in the repair request that you have dust *inside* the lens so that they understand the request completely. Once they receive your gear, they will evaluate it, and if it falls outside of a normal maintenance repair, they'll email you to let you know what they found, and they'll include an estimate to see if you want to move forward with the repair. You can get started at https://canon.us/repair

Re: RF 24-105 f/4 L - Dust inside rear element?

jrhoffman75 — Sun, 22 Mar 2026 20:09:52 GMT

@gnartS wrote:

Will canon actually clean dust/"things" inside the rear lens element that is absolutely affective image quality.

Looking inside my lens i can see a white blob (almost like fibre) towards the outside and a further smear of maybe dust towards the centre.

It shows clearly on blue skies as a large instinct dark circle at f/10 on my R6 and a very very obvious blob(s) at f/16 and narrower.

Im certain its not sensor dust:-

- The blob changes size as the lens is zoomed

- The blobs still exist but in a slightly different position when used on my crop R7. Its gone on my R6 zoomed in past about 40mm (its on the top middle edge).

- My 100-400 is clean taking the same test shots.

Lens is about 5 years old, bought new. Its been there at least a year.

My RF 16/2.8 has similar but nowhere near as bad issue.

What are the options here ? The lens is far too expensive to dump but its also only about half usable now unless i zoom in or make sure theres no sky in a shot. Yes i could edit every image but video its even harder.

R6, 24mm f/22. Right hand, top and centre blobR7, 24mm (so 40ish). Centre visible, right visible. Top cropped off with APS-C

That looks like fungus. Isolate it from your other camera gear because it can spread. Besides being on the elements it could also attack the coating.

Re: RF 24-105 f/4 L - Dust inside rear element?

JeffXB — Mon, 23 Mar 2026 13:45:44 GMT

I moved to the Philippines last year and one of the first things I did was invest in a dry cabinet (90 liter). If you don’t have one, you might consider getting one. Will help again fungi and other issues relegated to living in tropical and sub tropical environments.

Re: RF 24-105 f/4 L - Dust inside rear element?

gnartS — Mon, 23 Mar 2026 14:21:39 GMT

Have seen those but not really travel portable when spending 2-3 months in a place typically. Nor would be that useful when i lived in the Philippines with the power cuts but thats very regional.

Thinking about it the lens has been in the UK for 95% of the time since i had it (post covid) which really shouldnt get growth. Canon did open it and replace the front element 2-3 years ago for a crack.

Im going to have to find a 3rd party to clean or replace that element if Canon wont touch it.

Re: RF 24-105 f/4 L - Dust inside rear element?

ebiggs1 — Mon, 23 Mar 2026 15:43:29 GMT

"Im going to have to find a 3rd party to clean or replace that element if Canon wont touch it."

No shop is going to touch it, if it is fungus and I agree with JRH it looks like it. Two reasons, one "because it can spread", so they can't take the risk. And two, if it damaged the lens coating it not repairable period. Replace is the only option, either the element assembly or the entire lens.

Re: RF 24-105 f/4 L - Dust inside rear element?

ebiggs1 — Mon, 23 Mar 2026 15:48:18 GMT

"A clean and check does *not* include taking apart the lens to clean the individual elements."

Correct but it will evaluate the lens and Canon will let the owner know if there is a deeper problem. It is a multi-point maintenance service that makes sure optical performance and mechanical performance is where it should be. When I was full time I had a C&C done several times by CPS. The lenses or camera always came back looking brand new. I am not a person that ever 'babied' my gear. It either did what I wanted it to or it didn't. No in between as it has to if it's your job. However, I never remember having or had a lens with that much foreign junk inside my lens.

Re: RF 24-105 f/4 L - Dust inside rear element?

gnartS — Mon, 30 Mar 2026 04:05:55 GMT

Rear assembly and yes if they want to replace the rear element fine.

But not binning a 6 year old supposed L series lens (that was opened by Canon to replace a front element 2 years ago) and having to fork out thousands for this.
First time in several decades ive ever seen this on any lens