Just moving in to the 4X5 world and I'm as bit confused on the use of filters su ch as polarizers, ND's, ect. - in the 35mm world your screw these babies on the front for circular polarizers, add an attachment to the front on ND's - welll, y ou understand. In the 4X5 world do all filters go BEHIND the lens like a gel? o r..how???? Can anyone direct me to a tutorial or site? Thanks.