What polariser filter for sigma 10-20mm

i am currently using a cokin filter system, but the balck frame appeared at 13mm upward. Any advice? thanks

My first question would be do you really need a polariser with such a wide lens?

The first problem is vignetting - dark corners where the lens is so wide the filter cuts off the edges.

The second is that polarisation varies across the sky, so with very wide lenses polarisers cause banding effects.

The third thought is that with such wide lenses the sky light is arriving at the lens quite obliquely. This makes the corners darken naturally and, coupled with the lens's own vignetting we get a nice effect without polarisation.

If you really want a polariser then an immense and expensibe screw in design is really what you would need. Look at Hoya, B+W, Heliopan, etc.

Have you got the wide filter holder? There is a Cokin filter holder specifically for wide angle lenses, which only takes one filter. I have used it in the past with no problems at 10mm on this lens. The standard filter holder is not suitable for this lens. However, I never used a Cokin polariser, I used a screw-in Hoya one that worked ok except you can get uneven polarisation across the picture. But the wide adaptor certainly works fine with ND filters.

I would concur with John on this. I used a slimmer (single)filter holder on my 10-20 and there was noticeable vignetting from 10-13/14mm.

I reckoned my only option when it came to putting filters in front of this particular lens was to invest in a more expensive filter system. In the end I sold the 10-20 because I found my 17-70 was perfectly suitable foor the wide angle shots I was taking.

Certainly with a polariser the vignetting was worse but didnt want to spend a chunk of money on a screw-on filter for the 10-20mm.

thanks for the replies, particularly to John. i did come across the banding on the sky and could not figure out what has caused it or just thought an issue on comprssion. i found the cokin wide angle holder on ebay, and maybe try it, but i do not want to invest any more on another CP filer, but i prefer to leave it off if it causes too much loss in image quality. Has anyone tried Kood P series filter? no good at all?