Just noticed a fairly large piece of dust on one of the rear internal lens elements on the Canon Zoom Lens EF 24-105mm L IS USM after reviewing some video footage. It was noticeable when shooting the sky. Ran some tests and it presents a issue when shooting at F 8 and above. Not visible when shooting under F 8.

Has anyone had issues with this lens with dust getting inside the lens?

I am wondering if the zoom extension of the front tube is pulling in any dust that may collect on it when using the zoom, when it extends out and in?

Regards
Steve

Have Canon fix it, assuming you are under warranty. If you are not, I would still get it fixed, that isn't a cheapo lens.

Dan

Hi Steve,

You need to double check maybe dust in sensor. Change another the lens and if you still see a issue, for sure your camera have dust in sensor.

Cuong Dinh

Yeah, I would definitely double check to make sure it's really the lens and not the sensor; I don't think it's common for dust in the lens to show up. If you haven't already done this, use the same body with a different lens or two at small f stops, to make sure it's not sensor dust you're seeing.

I can see a spec of something in the internal lens.

I can see a spec of something in the internal lens.

I'm sure that's true, but it doesn't rule out sensor dust. In fact, sensor dust is still a far more likely cause of your issue.

Take a test shot with a different lens.

Dear Steve,

You may be able to get the speck of dust, in the lens, if it is actually there, to move.

Sometimes you can get it to move to the side, out of the way.

I'm sure that's true, but it doesn't rule out sensor dust. In fact, sensor dust is still a far more likely cause of your issue.

Take a test shot with a different lens.

Right. I can see dust in most of my lenses, but it never shows in my photos. If you want to know for sure where the problem is, try different lenses, since sensor dust is a problem far more often than lens dust (in my experience anyway).

If it goes away at lower f-stop settings, it is likely not sensor dust.

If it goes away at lower f-stop settings, it is likely not sensor dust.

That is not correct. It is normal for sensor dust to go away at lower (wider) f-stop settings.

How would sensor dust go out of focus when the iris changes?

How would sensor dust go out of focus when the iris changes?

Same reason that you have a shadow in sunlight and no shadow in overcast. The filters on top of the sensor can be as thick as 2.5mm. At wide f-numbers, the light is "soft", coming from many angles, causing the dust particle to cast a large, diffuse shadow, resulting in a very tiny reduction in contrast over many pixels. At narrow f-numbers, the light is "hard", coming from just one direction, and therefore casting a dark shadow on one small spot.

"The filters on top of the sensor can be as thick as 2.5mm."

That is something I didn't know. There is a lot to learn when shifting from a video camera with integrated lens to a still camera with interchangeable lenses.