Apologies if this question has already been addressed, but by what I could tell actual mathematical calculations haven't been brought up.
Right now I have an Alan Gordon Mark V director's viewfinder. I'm trying to figure out what the exact focal lengths (Give or take 2-3 millimeter) would be for commonly used sensor sizes such as full frame, Canon aps-c, and the Red Scarlet.
After calling Alan Gordon this is what I know for sure. The 35mm window is based off of super 35 3-perf film, 24.9 x 13.9. My baseline that would remain consistent on the viewfinder for these calculations would be