Fish-eye shader: distortion in only x or y direction?

[ArcadeHall]

I have a question about the fish-eye shader: is it possible to add a barrel distortion which only works in x or y direction of the image? I have looked at the formulas in the fish-eye shader, but that's over my head. I have a webcam which has a fish-eye distortion which can be corrected by a negative power in the fish-eye shader. But still the image looks a bit like this: )==(. I only need some correction in the x direction, but not y, since the lines are straight vertically. Can you give me a formula for this perhaps?

[exeldro]

can you test if 4582bad works for your use case?

[ArcadeHall]

Yes, now I can correct the X and Y distortion seperately, thank you very much!
Unfortunately now another distortion is visible: not a barrel distortion, but a cylindrical distortion. It looks a like reading a letter through a long drink glass laid down (horizontal, I hope it makes sense). Do you have a formula for cylindrical distortion (x and y separate if possible)?