Hello, Acording to Voigtlander data, Heliar 120/4.5 lens covers 8 1/2 x 10cm wide open. I wonder if it could be used with 9x12, if so, which f/stop has to be put to start covering 9x12 format? Has someone checked it? I am not sure if I should make a bayonet flange for it to use it with Bergheil 9x12. regards.