This is sort of tangentially related to the RA4 reversal processing thread, but not so much that I'd get away with mentioning it there ... Anyway, I want to shoot RA4 in-camera as a paper negative. Probably Kodak Supra Endura. Having read around and talked to a couple of people who have done this, there's a bunch of difference approaches. The idea I guess is to get the colour balance on the negative as accurate as possible (I actually want to reversal process them eventually aswell, hence the tangential connection with the above). So in order to do this we need to ... Filter for the magenta mask on the negative base. Filter for the fact that RA4 paper is tungsten sensitive Add filtration corresponding to the starter filter pack recommended for the paper we're using. And typically then mess around some more with some small filtering adjustments to get the colour balance spot on. I've seen this done seperately ... ie 85B for the daylight/tungsten conversion if shooting in daylight, then some unexposed but developed sheet film to filter for the negative mask, and then some CC or CP filters to make up the starter filter pack. I've also seen it done just using filter packs , ie that photo.net thread, where for example in one shot he uses 155Y + 75M (and some UV + IR filters). So, the question is, is there some way of finding out the equivalence here between various named or un-named filters and their CMY equivalents. Is there a table somewhere that gives, for example, all the Wratten filter numbers and the filtration in CMY form that you could use instead ? IE an 85B corresponds to 20Y + 10M or whatever. Is there some way of working out what the CMY equivalent of the magenta mask on C-41 film is ? (or at least some reasonable average of mask colour, I know most C-41 films have differently coloured masks).