I recently purchased a Goerz Series III, No 3 210 mm lens in barrell. Serial # 65213. The numbers that are engraved on the side of the barrel seem a little different from any that I have seen. They are: 4.6, 6, 12, 24, 48, 96, 192, 384. Are these actual f stops or a different system? If so, how do I convert? Thanks.

-- Dave Hammaker (dhammaker@aol.com), March 04, 2001

Answers

The first standardized series of F-numbers listed by Kingslake was: 1.1 1.6 2.2 3.3 4.5 6.3 9 12.5 18 25 36 50 71 100. Your numbers are similar but not exact. There were also two systems of F-numbers based on the relative image illumination--the Uniform System (US) and a set of numbers devised by a Zeiss lens designer (Paul Rudolph). I'm at a loss as to whether these apply! The US system is based on the square of today's f-number divided by 16. (ex: f/4 equals 4x4/16 or US1.) According to Kingslake, Rudolph's numbers are derived from "the appromimate value of 10,000/N-squared. Thus, f/9 became 128 in this system." Sounds like fuzzy math!

Where does this leave you? You could measure your lens openings and divide by the focal length to see if your numbers correspond. Wide open, your aperture should be about 45mm wide (210/4.6=45.6). You might also try some tests assuming that your apertures are close to modern, standard scales. Your f12 looks alot like f11 and f22 is pretty close to f24--again assuming your scale measures the aperture vs immage illumination.

If the iris does not "click-stop" you might be able to approximate modern f-stops. Rotating the iris between 6 and 12 will most likely give you about f8. If your really bothered by the old scale, SK Grimes or another shop might be able to recalibrate the apertures and add a new plate showing standard settings.

Hope this helps. By the way, do you know how old your dagor is? The list of serial numbers I have begins in 1902 with #70,

-- Dave Willison (dwillisart@aol.com), March 05, 2001.

I have a photocopy of a 1951 Goerz American catalog. It includes a conversion chart from f-stops to Uniform System (US) stops and also to "Stolze System as used on German-made Lenses". I suspect this is the system used on your Dagor. Is your lens marked "Berlin" on the front? Also, is it actually labeled "Dagor" or is it "Doppel-Anastigmat" or "Double-Anastigmat? The f-stop/Stolze System equivalents are:

f6.8 = 4.6, f8 = 6, f11.3 = 12, f16 = 24, f22.6 =48, f32 = 96,

f45 = 192, f64 = 348

There is a serial number list in circulation for American Goerz lenses. It is my understanding these numbers do not apply to Berlin lenses.

-- Leonard Robertson (leonard@harrington-wa.com), March 05, 2001.

My guess would be the 4.6= f6.8, and from there the progression is as normal, 6=f8, 12=f11, 24=f16, 48=f22, 96=f32, 192=f45, 384=f64. It's some variation of the Uniform System I expect. The Uniform System doubles its value as this does.

-- Erik Ryberg (ryberg@seanet.com), March 06, 2001.

I think its German. It actually says "Doppel Anistigmatic". Thanks for the answers.

dave

-- Dave Hammaker (dhammaker@aol.com), March 09, 2001.