I have a 6 1/2" Voightlander Dynar lens in shutter that I'm attempting to use on 4x5(my first journey into quirky lens land). The shutter is broken but I'm using it with a speed graphic. The aperture scale has fallen off the shutter.

I was wondering how I could figure out an aperture scale? I believe the lens is f5.6 wide open. Is there a formula for figuring out different apertures?

Thanks!