DK Thompson , Mar 10, 2008; 09:41 p.m.
try 15...10M is about a grade 2, or the equivalent of no filtration. 20 is just shy of 2 1/2. the difference between the two, imho, is not enough to blow out a background. best way to judge it is to use the filtration cheat sheet that would come with the paper--kodak, agfa, ilford etc have (had) them. the corresponding CC numbers for the filer pack--grade numbers. follow that as you would if using PC/VC filters. Start there, and if you can get the concept of the VC filters--dialing in filter packs will be pretty easy. If that doesn't help-- start by looking at how contrast works in the first place--back to basics. skip the yellow/ magenta filters and use VC filters. hope this helps.