I had an unfortunate incident that damaged under-the-lens multi-grade filter. That is, I accidentally hit the top of film cleaner spray and spritzed some of the stuff on filter. That resulted in partial damage to the surface. Now I have a replacement. THAT allows me to do some testing on the effects of under-the-lens MG contrast filters! I always wondered how much, if any, degradation there is to have under-the-lens filters. I hear there is none. Then next question is, how much damage is too much. These filters are so easy to damage and hard to clean.... There has to be a limit where impact is negligible and tolerable. My idea is this.... Have some kind of reference negative and print set the enlarger head high to simulate high magnification printing. I'll use 5x7 paper to cut down on a cost. (will be printing just a part of the image) Then... 1) print with no filter - reference #1 2) print with over the film filter (undamaged) - reference #2 3) print with under the lens filter (undamaged) - reference #3 4) print with under the lens filter (already damaged by spray) 5) print with under the lens filter (scratch some with sand paper) 6) print with under the lens filter (severely scratch with sand paper) Would this test procedure sound reasonable? What kind of subject will make good test negative? I'm thinking something high contrast with sharp lines.