Hello,

I just got a 7" Goerz dagor, a really ancient thing, and it uses "US Stops" which are on the barrel 2.8, 4, 8, 16, 32, 64, 128, 256. As you can see, the numbers more or less double each stop. Since this is an f6.8 lens can I assume that the 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 between the 64 and 16 (it's real close to the 16). . ..

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

-- Erik Ryberg (ryberg@seanet.com), January 19, 1999

Answers

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.

-- Rob Rothman (robrothman@worldnet.att.net), January 19, 1999.

Actually Rob, the "US Stops" system is one of the old ways apertures were designated. 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 Weston, etc.) was "US 256". But Adams, fearing that they would be mistaken for a highway suggested using the 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 between the pictorialists

-- Ellis Vener (evphoto@insync.net), January 20, 1999.

Actually Rob, the "US Stops" system is one of the old ways apertures were designated. 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 Weston, etc.) was "US 256". But Adams, fearing that they would be mistaken for a highway suggested using the 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 between the pictorialists and their school of "straight," sharp photography.

-- Ellis Vener (evphoto@insync.net), January 20, 1999.

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).

-- Ron Shaw (shaw9@llnl.gov), January 21, 1999.

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 Briggs (ms.briggs@cwix.com), January 23, 1999.

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.

-- Michael A. Smith (smitcham@epix.net), January 27, 1999.