– The largest filterholder there is on the market, the Cokin X-pro.
– A spare lenscap so I could use its bayonet for easy attachment to the lens.
– thick black paper (backgroundpaper) to cover the open space between the holder and trfnal (The Ring Formely Known As Lenscap).
The Cokin X-pro filterholder has a large enough diameter to avoid vignetting (working on full-frame), even when shifting the 17mm to the maximum setting. But, strangely enough, the polariser has a smaller diameter than the holder itself. I’d say that’s a serious design flaw: it means the rim of the filter causes vignetting at maximum shifting… No vignetting problems when using Cokin rectangular filters but I could not find a manufacturer that makes them large enough (130x170mm). Cokin only produces round polarisers…