hi ! (excuse me for this question, but i'm a beginner) i have a Durst F60 enlarger. Naturally, there is the filter drawer, where i know i can put the contrast filters for multigrade papers, but there's also a red filter, which is integrated in the enlarger head, that can be used or not. when i use it, turning a little red knob, the projected image becomes red. i can't understand what's its task : maybe it is useful to project the image onto the paper without exposing it ? thanks for your answers, and excuse me for my english.......