Old Aperture scape on a Hermagis lens

[Hugo Zhang]

I need to have a modern translation of the old aperture scale on my Hermagis Apl No.5 f=310mm Serie II lens. It starts at 3/4, then 1, 2, 4, 8, 16 and 32. I poped the lens on my 10x20, it almost covers it like my 12" Dagor. Truly amazing. Thanks.

[Mark Sawyer]

That would be the old U.S. System, aka Uniform System.

U.S. 1 = f/4
U.S. 2 = f/5.6
U.S. 4 = f/8
U.S. 8 = f/11
U.S. 16 = f/16
U.S. 32 = f/22
etc.

The U.S. System doubled/halved every stop, as that's what the volume of light did.

The f/stop System doubled/halved every other stop, as that's how the math came out when the focal length was divided by the aperture.

[Ole Tjugen]

Hermagis would use the French system, not US.

French 1 = f/10.

Doubling or halving for each step, so f/5 is French 1/2; f/20 is French 2.

So 3/4 is about f:7.2 - a very common maximum aperture for an aplanat!

[Mark Sawyer]

Ole, I'm not familiar with the French system. Is the translation done by just multiplying the French System number by ten to get the f/stop value?

French 0.5 = f/5
French 1 = f/10
French 2 = f/20

Would that imply the Hermagis' French 32 would be f/320?

(Always trying to learn; a little knowledge is a dangerous thing!)

[Ole Tjugen]

No, it's not simply multiplying by 10.

I was tired and half drunk when I wrote the above, or I would have provided a better explanation:

The most common "non-fstop" aperture scales on old lenses are:

US - US 1=F/4
Stolze - Stolze 1 = F/3.16
"French" - Fr 1 = F/10

These three double the value for each f-stop.

French system vs. F-stops:

1/8 = F/3.4
1/4 = F/5
1/2 = F/6.8
1 = F/10
2 = F/14
4 = F/20
8 = F/28

and so on. The US was mostly used in USA; Stolze was fairly common in Germany, "the French system" in France and early Steinheil lenses. Finding out whether a lens is marked in US or Stolze can be tricky, since the're fairly close. But the French system is so different that it's generally obvious.

Then there's
Rudolph - Rudolph 1 = f/50, doubling for each step too, but in the other direction so that Rudolph 2 = F/36, 3 = F/25 and so on. Just about only used by Zeiss.

[Hugo Zhang]

Thanks, Ole! This is very helpful!

[Ernest Purdum]

As Ole says, the US system was common in the USA, particularly on Kodaks. So many 3A Folding Pocket Kodaks show up carrying "F4" Rapid Rectilinear lenses.

The origin of the system is, however, British. "US" stands for "Uniform System" not, as often presumed, United States. The Royal Photographic Society proposed this method of stop markings.

[Ole Tjugen]

... The origin of the system is, however, British. "US" stands for "Uniform System" not, as often presumed, United States. The Royal Photographic Society proposed this method of stop markings.

With the predictable result that most British lens makers chose not to use it. In my experience the majority of British lenses are marked in AU - or "Arbitrary Units".

[john wilton]

Ole, I imagine it is safe to assume that 3/5 is 7.7 for this old pre-Dagor Serie III?

Unrelated question...The aperture control is a bit too stiff for easy use. Is it reasonably safe to flood clean the diaphragm with Ronsonol (after removing the lens cells of course)?

French system vs. F-stops:

1/8 = F/3.4
1/4 = F/5
1/2 = F/6.8
1 = F/10
2 = F/14
4 = F/20
8 = F/28

[seawolf66]

May I jump in here ,and check something on F/-stops: I picked up a Dallmeyer Enlarging Anastigmat lens 8-1/2" F/4.5 # 320599 no series numbers or any thing else:

THe scale starts as 4.5 but the next f/-stop say [x2] then next doubles a=untils you get to x16 :

To use this lens I take it all I need to do is mulitply x2 by 4.5 or x16 by 4.5 ::
Any corrections on my thoughts : photo attached: