Yesterday I tried to test my Durst M 600 with a 35mm negative to enlarge of size 20x25cm. Enlarging lens: Schneider Kreuznach @f/8 50mm. Paper: MCP 312 Without filter: Paper speed is ISO 400 require 20.2 sec(f-stop printing). With Grade 3 filter: Paper speed is ISO 160 require 64 sec(approximately). Paper: Adox Vario Classic With Grade 3 filter: Paper speed is ISO 40 require 256 sec(approximately). Filter was placed under the lens. Paper Developer: ECO 4812 Moersch. Question: Is it normal to have such a long exposure times for paper.