EX Aperture Scale

[Diane Maher]

I have a Beach Multi-Focal Series A lens in an old Wollensak Studio shutter and the aperture scale is shown in units of EX (11.7 is wide open and 5 is the smallest diameter of the aperture). Does anyone know about that scale and how it compares to today's f-stop system?

Diane

[Jim Galli]

Diane, I've yet to find any original literature that explains that weird scale....but....if you force 11.7 to equal f4.5 and 11 = f5.6 and count up in increments from there you'll find it is based on a Wollensak f4.5 Velostigmat and acts accordingly.

[Diane Maher]

Thanks Jim!