Aperture scale on shutter Pi-ALPHAX

[originalphoto]

I have a Wollesak 61/4'' (159mm) f/12.5 lens with Pi-ALPHAX shutter. Aperture scale shows 16, 11, 8, 5.6, 4, 2.8, 1.9. My question is if this is an original shutter for this lens? if yes, how to convert this scale to current standard F-stop?

[Dan Fromm]

(1) No. f/1.9 doesn't mean f/12.5.

(2) Open the shutter by setting it to "T" and firing it. Open the diaphragm as wide as it will go. Look into the front of the lens, slowly close the diaphragm until the iris is just visible through the front of the lens. The number (or space between numbers) that the aperture indicator points to corresponds to f/12.5. And there you are. Remember, the marked apertures are one stop apart.

[Steve Goldstein]

It is certainly not the original shutter. It probably came from an old oscilloscope camera. But Dan is correct, it's easy enough to recalibrate the aperture markings as he outlined.