I want a strong filter that will darken a brilliant red object on B & W film. I think a Wratten 44A is a "minus red" filter. My searches tell me it's a cyan or blue-green flter. I'd like to get a 67mm glass filter. Is there another filter I should be looking for; it does not have to be truly "minus red" Any suggestions on a good primer (book or site) on filter use in 1) b & w film and 2) color film? I guess the best are A. Adams for b&w and Horenstein books on color. Any good discussions of filter fundamentals elsewhere? Thanks.