So I'm delving into the mysteries of historical lenses and bought an unknown lens.
I'm going to try it out and I've noticed an embossed numerical aperture scale reading 1,2,3,4,5?
I haven't been able to find anything about this specific system and would appreciate anything to enlighten me.
I'm not too sure of it's age or design but there is only one element front and one rear. It measures 4''/10cms in length and 2.5''/6cms diameter. Everything looks, feels and works correctly and seems authentic but I just don't know. If all else fails, I thought about doing some tests exposing wide open to try and calculate the number 1 aperture and work the rest out from there...