control elements: paper sensitivity, time, f-stop, light output, head height.
Light Output: One thing that you did not consider is the light bulb itself. My Durst M600 is a very bright enlarger, I went down from the original 150w bulb to a 75w bulb, and sometimes I want a 40w or lower bulb, for less light, to get a longer exposure time.
- You may want to change bulbs for different papers, higher wattage for a slow paper, lower wattage for a fast paper. But because bulb changing is a PIA, do this as the last option.
Head Height: Another is the height of the head of the enlarger above the baseboard. The closer it is, the higher the intensity of the light on the paper. The farther, less intensity on the paper. This applies to paper calibration and contact printing.
What I do not know, because I have not tried it is, with the same magnification, but with 2 different lenses 50mm and 80mm with the head at different heights to maintain the same image magnification, will the exposure be the same?