Originally Posted by
devb
I'm curious about this too. I have the same shutter with the same markings, with matching 210/6.8 lens cells. BUT, I sometimes stick my orphaned Symmar 150/5.6 cells in the shutter.
I had been under the impression that I could derive the actual iris diameter from the focal length / f-number and use that to calculate the f-number for the other lens (in this case, f/11 on the 210 scale is 19.09 mm, which would be f/7.8 for the 150 scale) but it didn't quite work. I have to stop the lens down 1 2/3 stops further than my numbers say to. I wish I understood why. Maybe it's because the cells are different? It might work for you though.
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