UWA with CPL, good or bad?

[stylgeo]

Have had my 10-20 for 3 years now, and have always avoided buying a CPL for it, because of all the reports I've read about uneven polarisation, especially in the sky.
Anyone uses a CPL on an UWA? can someone post an example just to show this effect. I'm seriously thinking of buying one because I think I might be missing out, I always enjoyed the effect on my old kit lens. I could just buy a cheap one just to see the effect on my own but I am going on a trip soon and I would like some opinions, because If I do buy one, I'll opt for an extra slim expensive one, to keep the lens' sharpness and avoid vignetting.
Thanks!

 

[HoppyUK]

Get a polariser, and enjoy! I use one a lot, and to be honest this 'uneven sky' thing has never bothered me. In fact, I've hardly ever noticed it with my Canon 10-22mm lens. Get a multi-coated one, to minimise flare.

Uneven polarising of the sky happens with ultra-wides because the polarising effect varies according to the angle of the sun, and as ultra-wides take in such a wide field of view, the polarising effect varies across the sky. Sometimes this is noticeable and sometimes it is not. If you don't like it, zoom out to a longer focal length, or just take the filter off.

Some examples and a tutorial here:
http://www.luminous-landscape.com/tutorials/polarizers.shtml

Hoya have a new polariser out in their HD range. It only cuts the light by just over one stop, as opposed to the usual two stops. But it's frighteningly expensive.

 

[stylgeo]

Thanks hoppy, this is what I needed! Appreciate you taking the time!

Will probably get myself a polariser now, but I won't spend more than £60 on it, so will have to do some shopping around

 

[HoppyUK]

No worries bud

Before you buy a cheapy, check this thread about filters and flare. There are some scary example pics. http://www.talkphotography.co.uk/forums/showthread.php?t=130960

But you'll be lucky at that price. You need 77mm for the 10-20 Sigma, and also a slimline mount to prevent vignetting with that very wide angle.

Check that at least the rear surface of the filter is coated - a single coating will reflect bright lights with a light blue colour. Green is almost certainly multi-coating, which is as good as it gets. Even most of the expensive polarisers are not coated on the front surface due to manufacturing difficulties so don't worry about that too much. But I think you will hit problems unless the rear surface is at least single coated. It's hard not to get the sun in the frame at 10mm, or certainly very close to it, so difficulties are almost unavoidable.

Check out the For Sale forums here. It's a really good marketplace but I guess you know that Post a Wanted ad.