"US" Fstops

[Erik Ryberg]

Hello,

I just got a 7" Goerz dagor, a really ancient thing, and it uses "US Stops" whic h are on the barrel 2.8, 4, 8, 16, 32, 64, 128, 256. As you can see, the number s more or less double each stop. Since this is an f6.8 lens can I assume that t he 2.8 = f6.8, the 4 = f8, the 8 = f11, the 16 = f16, the 32 = f22, the 64 = f32 , the 128 = f45, and the 256 = f64?

Or is it something more mysterious? I suspect it may be, because, the 128 falls equidistant between the 256 and 64, but the 32 is not at all equidistant betwee n the 64 and 16 (it's real close to the 16). . ..

Thanks for any help that saves me a whole lot of tests.

[Rob Rothman]

I wonder if somebody fitted a shutter/diaphragm to the lens without bothering to calibrate the aperture ring. With the exception of the first stop (marked from 2.8 to 4), each marked stop on your barrel actually represents two stops, not one. I'm not sure how to calibrate this lens properly, but you might try going under the darkcloth (to exclude extraneous light) and taking readings off the center of your groundglass with a spotmeter as you stop down the lens; this should at least give you a ballpark idea of whether you're stopping down two stops or one each time.

[Ellis Vener]

Actually Rob, the "US Stops" system is one of the old ways apertures were design ated. I was recently reading that one of the original names proposed for the "f/ 64" group of west coast photographers (Ansel Adams, Imogene Cunnigham, Edward We ston, etc.) was "US 256". But Adams, fearing that they would be mistaken for a highway suggested using th e new system of nomenclature for the same f/stop, hence f/64. This from the Mary Street Alinder biography of Ansel Adams. Why f/64/ to clearly draw the line bet ween the pictorialists

[Ellis Vener]

Actually Rob, the "US Stops" system is one of the old ways apertures were design ated. I was recently reading that one of the original names proposed for the "f/ 64" group of west coast photographers (Ansel Adams, Imogene Cunnigham, Edward We ston, etc.) was "US 256". But Adams, fearing that they would be mistaken for a highway suggested using th e new system of nomenclature for the same f/stop, hence f/64. This from the Mary Street Alinder biography of Ansel Adams. Why f/64/ to clearly draw the line bet ween the pictorialists and their school of "straight," sharp photography.

[Ron Shaw]

If you have another lens available, you can calibrate it easily (the same way you would calibrate a new shutter/diaphram assembly). Mount the known lens on your camera, and aim the camera at a brightly lit wall. The brighter the better. Set the aperture at a value both lenses cover (such as F8). Using you light meter (in reflective mode), take a reading at the center of your ground glass, and record the value. Next, mount the new unknown lens. Measuring the light as before, adjust your aperture until you get the same reading as the known lens. This is now the (F8) position. Once you have this, then you can calibrate the rest of the aperture scale by reading the light value as you stop down (or open up), for 1 stop differences (or whatever resolution you desire).

[Michael S. Briggs]

An old manual (copyright 1940 & 1943), "Kodak Reference Handbook, Materials, Process, Technique" answers this question.

One surprise: "U.S." stands for "Uniform System", not United States. The table gives the following correspondences: f8 = U.S. 4, f11 = U.S. 8, f16 = U.S. 16, f22 = U.S. 32, etc. The U.S. number doubles/halves for each 1 stop change. This agrees with what you guessed.

[Michael A.Smith]

US stops convert to F-stops like this: F 16 is the same as US 16.

Then double or halve for each US number. US256=f64; 128=f45; 64=f32; 32=f22; 16=f16; 8=f11; 4=f8; 2.8=f6.8

Hope that helps.

[seawolf66]

based on the fact the US number system is old you say 256=64[Then double or halve for each US number. US256=f64; 128=f45; 64=f32; 32=f22; 16=f16; 8=f11; 4=f8; 2.8=f6.8] now I have a scale that starts at 4 \\ 6 \\ 12 \\ 24 \\ 48 \\ 96\\
Now is this a US number scale or something else: thanks all:

[Glenn Thoreson]

There used to be at the very least, a half dozen different aperture systems in use. I have cross reference on a lot of them I'll try to find something for you, but I may or may not have any luck even finding the stuff. U.S. system is easy. as mentioned, f/16 is f/16 and you just count up or down from there for modern stops. The other one may not be so simple. At least it's better than the old Zeiss system where wide open was 1024.

[seawolf66]

Glenn Thoreson: Thanks a lot , I hope you have success: