Hello, I am trying remount a Super Angulon 65/8 lens that I have acquired on Sinar DB mount in a shutter. It fits in a Copal 0 that I have but the the aperture marks on the shutter are for different lens (135mm). There should be a formula for the diameter of the aperture opening for given focal length and stops but I could not find it. Please help if you know how to calculate it! Thanks in advance luben P.S. The aperture in the Sinar mount is missing so I could not just measure it.