How wide angle with Cokin P holder???

How wide of a lens can I go with before I'm going to start having a problem with using a non-wide angle Cokin P adaptor?? I'll be shopping for a wide lens once my bank account recovers from my camera package purchase but I intend to use my GND set extensively with this lens and don't want the holder to become visible when backed right out. I'm sure that 17mm is safe but wouldn't mind getting a little closer to 12 or 10mm if possible.

Thanks

You can shoot 12mm but no lower. I used to use P filters with the Sigma 10-20mm(on a 20D) and after 12mm it was fine but below it you could see the filter.

I now use the Ps with my 17-40mm(on a 1D2n) and there are no problems

Neil

I often use the Cokin P filter system combined with a Hoya slim circular polarizer (with front threads). This way I have the CP filter that can easily be used on any lens even with lens shades, and then the P filter holder that can also be attached on top of the CP or by itself, depending on what I need. To minimize vignetting I have cut the P holder so that there is now only one slot into which a GND filter will slide (or any other filter). With this combo I get these results:

5D with a 16-35 (mkI)
No CP (or UV) filter, just modified P holder: No vignetting at any focal length.
With Hoya CP filter and modified P holder: Vignetting begins around 20.5mm.

5D with a 24-70
No CP (or UV) filter, just modified P holder: No vignetting at any focal length.
With Hoya CP filter and modified P holder: Vignetting begins around 27mm.

Super, thanks guys

Canon EOS 30D + Cokin P wide angle holder and EF-S 10-22: slight vignetting in top corners at 10mm but gone around 11mm. My 350D/XT didn't have issues even at 10mm.

My xti starts to vignette at 15mm w/ the cokin wide holder and a CPL. I have not noticed any problems w/o the CPL.

Do you use the middle slot or the slot closest to the lens?