After going thru the other thread it made me thinking once again. What I often do is to make 4x5 prints from 35mm using the 80mm lens and when I switch to 8x10 I use the 50mm lens. Assuming that the f/stop marking on the lens is accurate and the magnification for the 4x5 prints is 4x and 8x10 prints is 8x. Also assuming that the same aperture is to be used (I actually use 1 stop larger when go to 8x10). I always use a color analyzer to determine printing time which is simple. However, I wonder how do one calculate? I think I would find the answer in the next few days but I wonder what you're all thinking?