Re: the CPL discussion on ultrawide, here are some shots I made with the Sigma 10-20 f4.5 with CPL. I was very much a "noob", had my K200D for less than 30 days at the time, and was shooting JPEG only. No PP.
I still love these shots today. It may not be to everyone's liking. But I know I would much rather have the CPL than not for these shots. When I went inside the castle, I did take the polarizer off. It loses about 2 stops of light, and the K200D only maxed at 1600 ISO, and you really didn't want to use that ISO on that camera, ever. Even 800 was pushing it. These are SOOC JPEGs. All taken at 10mm.
First one. The horizon has a lighter sky color. But there is no big dark patch as in the fstoppers example. The sky gradient color looks very nice to me. And I know without it, the picture would be much worse.
In the following, I think the CPL did its job nicely, except for the vignetting. Would not have wanted to be without the CPL.
In this one the sky is quite dark, but not too uneven. This is the result of wrong exposure. The K200D had a tendency to seriously underexpose, compared to current bodies. This can be compensated in post, even on a JPEG, but this is SOOC.
I actually like the gradient of the sky from top to bottom (horizon). There is no big dark patch in the sky. The worst thing I can say here is the vignetting from the filter.
In the following shot, I will admit sky looks somewhat patchy. It hadn't bothered me until this thread. Not quite sure how/if this can be helped in post or not on a JPEG. I only use Lightroom classic for PP, but none here.