Are you using the older color head with the power supply, or the solid state s version? I am using the s version, with 81M and 71Y of filtration for grade 2 on arista paper ( I might have those backwards). This gives me an exposure of 15 seconds when going from 35mm to 8 x 10. Lens is about f5.6. Also, I use the condensor for B&W. I assume you are using B&W. When I tried the condensor with RA-4, I had exposure times of 5 to 7 seconds, and too much contrast, so I use the diffuser with RA-4.