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:

[Brian Bullen]

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)?
John, I have a Heliar that came with a frozen aperture ring. I had to unscrew a tiny set screw on the ring, remove the ring from the threads,(There was a huge amount of junk in there. ) clean the threads with alcohol and toothbrush. I applied a small amount of lithium grease to the threads, put everything back together. Searched a while for the hole for the set screw, which I found with a bright light shining in there. Put it all back together and it works super smoothly now. I don't know if this helps for your case but it made everything work perfectly for me.

[Paul Fitzgerald]

Lauren,

"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:"

its an enlarging lens so that is probably an exposure scale in full stops down from 4.5, 6.8, 9, 13, 18, 26

John,

"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)?"

NO, the iris blades may be a type of plastic / vulanized rubber, Ronsonol would ruin those.

[john wilton]

Paul,
"NO, the iris blades may be a type of plastic / vulanized rubber, Ronsonol would ruin those."

Thanks for the heads up. They don't look very metallic. Is there a way to loosen it up a bit short of major disassembly? Can't find much in the archives. Is there a safe solvent? In one post CP Goerz mentions a drop of gun oil on the ring, but where? Outside the barrel or inside?:
"PS:For a stiff iris just use some light gun oil or 3 in 1, wipe any excess from the blades with a piece of absorbent paper but as mentioned the main sticking point is the dial itself so a drop or two top and bottom will work wonders there too. Don't force anything, let the oil do its work and you'll be fine." But he was talking about a much more recent Artar and perhaps doesn't apply to 19th century iris.

[john wilton]

Brian,

In searching for a set screw I figured out how to remove the lens barrel from the focus mount; this removed about 75% of the resistance. Tomorrow I'll try some more to see how to get the aperture control sleeve/tube off. The only screw I can see (in the pic) is transferring rotation to the iris mechanism inside, and is not holding the tube on.

[seawolf66]

Nine times out of ten the problem with the Iris control ring is that dirty over the years has come to rest there, gun oil ,three in one oil ,or CRC spray, WD-40 : all these can be used on the outside of the barrel or brass lenses for between the body of the control ring and the body:

[Paul Fitzgerald]

John,

"Thanks for the heads up. They don't look very metallic. Is there a way to loosen it up a bit short of major disassembly?"

Never worked on a focusing mount version but Goerz used 2 versions of their patented PITA aperture assemblies, both are a bloody nightmare to re-assemble. Anything you can do to NOT dis-assemble it would be a good thing.

Version 1 is a joggler's trick, worse than a Compur 00.

Version 2 is, in all likelihood, the actual reason for the start of WWI. Re-assembly was a trade secret that few techs remember today. This is why you find too many Goerz lenses with broken or missing blades or the whole assembly ripped out and thrown away.

[john wilton]

Oh, the simple things are best. A micro-bead of 3in1 oil around the seam between the brass base of the barrel and the aperture control and working it back a few (dozen) times...it is now as smooth as silk. Perhaps inanimate objects can have feelings: I sense this one is happy to be brought back to life. Anyway, I'm happy, thanks guys. Now to see if it covers 5x7. Apologies to Hermagis for hijacking this thread.

[Brian Bullen]

John glad you got things moving again. Judging from the second photo and what Paul said I'm glad you didn't have to dis-assemble the entire lens. Good luck with the "new"lens!