Recently was able to trade my Sinar P for a nice arca-swiss f-metric with a compendium bellows. Long story short I found http://www.ebay.com/itm/13056738582...NX:IT&_trksid=p3984.m1439.l2649#ht_950wt_1231 and snapped it up seeing as how it goes for $400+ on bhphoto/etc. I also bought a 4" Schneider linear polarizer for $140 and everything arrived yesterday. Unfortunately the glass filter is a smidgen too large for the filter holder. The Schneider filter is not returnable, otherwise I'd just find an appropriately sized 100mm polarizer, additionally I'd really prefer to keep my filter system on the compendium hood to save time in the field when swapping lenses out. I know 4" is 101.6mm but from everything I'd read 4" filters and 100mm filters were interchangeable in practice? Is that mistaken? I see a few ways to proceed: 1. Grind down the 4" polarizer to fit in the arca holder. Anyone have any experience with this? 2. Buy a 4" filter holder and all the appropriate step up adapters for all my lenses - not tempting. Thoughts?