I have a Sigma 10-20, cokin do a special wide angle holder which i've had no problems with it showing at the widest settings, the only downfall is it only holds 1 filter as opposed to the standard which holds three. The cokin pro series does hold three filters and is designed with ultra wide in mind but costs somewhere in the region of £100 or so for the holder :O
I heard there was still some show with the wide cokin P holders at lengths under 14 so I had ruled it out... but what you say might require more investigation thanks
Also iGi the Lee's are up there on my list of possibles...... just a bit more pricey.
77mm Hoya R72 Infrared filter
POTN Archives said:Good
Canon EF-S 10-22mm f/3.5-4.5
Canon EF 17-40mm f/4 L
Canon EF-S 17-85 f/4-5.6 IS
Canon EF 24-70mm f/2.8 L
Canon EF 24-105mm f/4 L IS
Canon EF 28-135mm/3.5-5.6 IS
Canon EF 28mm f/2.8
Canon EF 50mm f/1.8 MKI
Canon EF 50mm f/1.8 MKII
Canon EF 70-200mm f/4 L
Canon EF 75-300mm f/4-5.6 IS
Canon EF 135mm f/2 L
Canon EF 100-400mm f/4-5.6 L IS
Canon EF 100mm f/2.8 Macro
Canon TS-E 24mm f/3.5 L
MTO 500mm f/8
Sigma 400mm f/5.6
Tamron 28-300mm XR
Bad
Canon EF-S 18-55mm f/3.5-5.6
Canon EF 16-35mm f/2.8 L
Canon EF 20mm f/2.8
Canon EF 35mm f/2
Canon EF 24-85mm f/3.5-4.5
Canon EF 28-70mm f/2.8 L
Canon EF 28-105mm f/3.5-4.5
Canon EF 35-80mm f/4-5.6
Canon EF 50mm f/1.4
Canon EF 50mm f/2.5 Macro
Canon EF 70-200mm f/2.8 L IS
Canon EF 70-300mm f/4.5-5.6 DO
Canon EF 85mm f/1.8
Tamron 17-35mm
Tamron 19-35mm
Tamron 70-300mm Macro
Tokina 12-24mm