# Thread: What kind of lens has aperture scale in mm?

1. ## What kind of lens has aperture scale in mm?

I discovered a sample where aperture scale is marked in mm instead of stops. The scale starts from 6.8 and ends with 98. It is a fairly big lens. Only identifiable information is XVI1 (1 is in subscript) on the barrel.

Could this be a process lens or where this kind of scale might be useful?

2. ## Re: What kind of lens has aperture scale in mm?

For a time -- some time in the 1890s to early 1900s -- Carl Zeiss Jena scaled apertures in mm. See, e.g., the 1901 CZ London catalog, which has an extensive discussion. There's a link to it in the list.

XVIsub1 is very Zeissish. See the 1910 CZJ catalog p. 14, there's a link to it in the list too.

Other manufacturers have done this occasionally, for example I have some Reichert Neupolars made well after WW II with apertures scaled in mm. 50/3.5 and 100/6.3, both high performance macro lenses for use at magnifications above 1:1.

3. ## Re: What kind of lens has aperture scale in mm?

Lenses primarily meant for technical applications often were marked in this manner. Actually it is very practical,but requires good mathematical skills capable of mental calculations.

4. ## Re: What kind of lens has aperture scale in mm?

Originally Posted by Jim Noel
Lenses primarily meant for technical applications often were marked in this manner. Actually it is very practical,but requires good mathematical skills capable of mental calculations.
The only math skill required would be simple division, and you'd only need to be in the ballpark for practical purposes.

I've run across a few old lenses that had little marks on the aperture scale at 1 cm and 0.5 cm, or 1 inch and 0.5 inch aperture. That makes the calculations VERY simple.

5. ## Re: What kind of lens has aperture scale in mm?

Scales marked in mm are very useful with convertible sets, where different combinations would give different f stops wide open. I have a Zeiss Protar VII casket set with a barrel marked in mm, double Protars and Amatars often have a mm scale on the shutter alongside f stops, very useful. It's handy for bypassing bellows extension calculations too - maybe that's where it'd be useful with process lenses.

6. ## Re: What kind of lens has aperture scale in mm?

Originally Posted by Jim Noel
Actually it is very practical
I guess it should be very useful to calculate the effective aperture when we give bellows draw for a close focus...

I'd ask if the aperture in mm is the real hole or if it is the effective hole size, seen from the front, to give the value that's used in the f/ calculation...

7. ## Re: What kind of lens has aperture scale in mm?

Originally Posted by Pere Casals
...I'd ask if the aperture in mm is the real hole or if it is the effective hole size, seen from the front, to give the value that's used in the f/ calculation...
That would be the trick when using it with the casket set as mentioned by pjd. Different front cells would render slightly different sized effective apertures from the same raw aperture.

8. ## Re: What kind of lens has aperture scale in mm?

Originally Posted by Mark Sawyer
That would be the trick when using it with the casket set as mentioned by pjd.
OK, now I understand it, thanks for explaining it.

9. ## Re: What kind of lens has aperture scale in mm?

I figured you'd know it already, Pere, but some here may not. Your comment was just the perfect lead-in to my point.

10. ## Re: What kind of lens has aperture scale in mm?

Originally Posted by Mark Sawyer
That would be the trick when using it with the casket set as mentioned by pjd. Different front cells would render slightly different sized effective apertures from the same raw aperture.
The Tri Tran Signature Pictorialist Lens is a casket system with meniscus lens elements available in focal lengths from 9" to 30". To address this issue, the aperture scale is marked in Roman numerals from I to VI.