Help identifying a lens with a numeric aperture scale

[martin howard]

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...


Kind regards,

Martin

[Richard Rankin]

Look at this, towards the bottom and it might help explain the apertures.
Richard

http://throughavintagelens.com/category/working-with-vintage-cameras/

[Jim Jones]

Look at this, towards the bottom and it might help explain the apertures.
Richard

http://throughavintagelens.com/category/working-with-vintage-cameras/

Long ago I started photography with a lens much like that. The numbering system is arbitrary, and has nothing to do with the old US system. The maximum aperture on that lens is probably about f/14.

To determine the aperture, first check the approximate focal length with a distant subject. Then measure the aperture as seen through the front element for each of the numbers on the scale. The f/number is that diameter divided into the focal length. Having your eye some distance from the lens when measuring that diameter improves accuracy.

[martin howard]

Thanks you for your replies.

[Steven Tribe]

I have no real argument to back this up, but I have the impression that lenses marked with the linear 1,2,3... etc. scale were used specifically in early enlargement.
The exposure of papers in the darkroom is very much a trial and error activity where a linear scale would be just as good as a scale which represented "theoretical" 1/2 times. Especialy if the paper behaves in a non-linear manner.
I have one of these lenses, too.