Vingetting with CPF in one corner

I have a Canon EFS 15-85 on my 60D. When I use a circular polariser on low end of the zoom (15 - 20 mm) then I get this very strong vingetting in the upper right corner (see example below).
It is always the upper right corner. Why is that? Anything wrong with the CPF or the lens?

I am not sure why it is in the top right corner mostly but my 40D with Sigma 10-20 has the same problem. You need to get one of the slimline cpl's.

There shouldn't be any optical reason why you're getting that, so I'd have to guess that the filter itself is physically intruding into the image. If you're stacking the CPL with a UV or something, take the redundant stuff off to save 'depth', or invest in a slimline filter as mentioned above.
Sometimes if you're shooting really, really wide the CPL can give uneven results on skies and things, but this phenomenon presents more as 'sectors' or shading rather than only one corner!

BTW, you should NEVER stack filters!

Not only do you run the risk of creating dark corners, but you run the risk of getting your filters stuck together.

That may be because the sun is to your right as opposed to being low on the horizon. You can tell this by observing the shadow on the bicycle rider. FYI, a polarizier is least effective at noon and your profile doesn't indicate where you are. I would first of all as others have said, get rid of all filters except the CPL, and then shoot a subject where the sun is to your left, instead of the right. Ge t something where the sun is low, like at 10 AM or 4 PM and then rejudge.

drmaxx wrote in post #14459945
It is always the upper right corner. Why is that?

Most lenses aren't exactly centered, so when you using a filter that creates mechanical vignetting then you'll sometimes see it slightly worse in one corner than another. I see a bit in the upper left too. It doesn't mean the lens is going to be softer on one side than another or anything like that though.

"Most lenses aren't exactly centered"

Care to elaborate? The Canon EF-S 15-85mm is a pretty decent lens and I'd doubt it far enough off center to explain vignetting.

John from PA wrote in post #14463987
"Most lenses aren't exactly centered"

Care to elaborate? The Canon EF-S 15-85mm is a pretty decent lens and I'd doubt it far enough off center to explain vignetting.

Far enough that one side will mechanically vignette slightly more than another when the filter is in the way. With no filter you obviously would not see that amount of vignetting at all anyway.

Just explaining why one corner vignettes a bit more than another corner, not why the vignetting is occurring (although i think it is pretty obviously the filter is physically blocking the light).

If you stack enough filters together you'll see this with any lens and certainly my kit 18-55 (when I had it) and 10-22 showed slightly more of the filter in one corner than another. Can't remember if my 17-40 does or not, but certainly the 10-22 is just as sharp in all corners, so I never saw it as a problem.

I think it seems slightly worse in wide-angle lenses.

I can't subscribe to the argument that "most lenses aren't exactly centered" without some testing. I do feel as stated before that the corner to corner difference may be because the sun is to the right in the images posted by the OP. To me this would naturally cause more vignetting in the corner nearest the path of light. It isn't unlike flare; an experienced photographer can readily tell by looking at flare where the light source was positioned. I have three lenses that include a Sigma 17-50, a Canon 28-105 and a Canon 75-300. The Sigma and Canon 28-105mm will vignette at selective apertures with a polarizer mounted, sometimes quite markedly if the sun is low in the sky. However, if I shoot a white 4 x 6 foot test target indoors, with on camera flash and forcing the same aperture, then the vignetting is equal, at least to my eye and with DPP at 200%.

John from PA wrote in post #14465591
The Sigma and Canon 28-105mm will vignette at selective apertures with a polarizer mounted, sometimes quite markedly if the sun is low in the sky.

Maybe your correct then about the OP's issue, I've never noticed this. Only time I've ever seen as much vignette as in the OP's shot is when the filter is getting in the way and it will occur at pretty much any aperture and any subject. And in these cases the 'pattern' is always the same, even if I rotate the camera and is not perfectly aligned in all corners.

Maybe 'most' should be 'many' or 'some' some other non-zero number, just my admittedly limited experience.

alex.hondsmerk wrote in post #14460309
There shouldn't be any optical reason why you're getting that, so I'd have to guess that the filter itself is physically intruding into the image. If you're stacking the CPL with a UV or something, take the redundant stuff off to save 'depth', or invest in a slimline filter as mentioned above.

So this strong vingetting is somewhat 'new' for this lens-filter combo. Last time, I thought that I am just an idiot holding my pinky somewhat strange into the lens. Just barely, so that I couldn't see that in the 95% viewfinder range. But this time, I was sure that my fingers were nowhere near the lens.

So, last night I had a closer look at the lens and YEP: The CPF was stacked with the UV. I usually don't do that - and just forgot/ignored that I had it there. So it might very well be that the filter stack is intruding into the picture. This filter combo is 'new' for me and this is also the first two times that I got this uneven vingetting effect.

I'll test that as soon as I get some time (and some sun...).

Thank you all for your help and suggestions. As always, I am very impressed about all to great responses.

Lesson learnt: Stacking filters is baaaad!
Below two (almost) identical pics -- one with and the other without UV filter behind the CPF.
Thanks again everybody.