Rapid Rectilinear & Anastigmat lens testing

A long story with questions at the end...

The weather was very poor for most of this past long holiday weekend here in Houston, so I took advantage of the storms' keeping me indoors to do some lens testing. I have 3 lens components from Kodak 3A folding cameras:

• a B&L Rapid Rectilinear lens set
• a Kodak Anastigmet 170mm f6.3 lens set,
• a Kodamatic shutter, with speeds 1/2 through 1/150 and marked f/6.3 through f/45.

The Anastigmat lens came mounted in the Kodamatic shutter.

I have used both lens sets with this shutter and in general the negatives were overexposed, by several stops, compared with other exposures I made at the same time with other lenses - - nothing scientific.

My first thought was that the shutter speeds were probably slow, which would cause the overexposure problem. I have a shutter tester and I tested each speed (5 firings each speed, after exercising the shutter well) and found that none of the speeds was off by more than 1/2 stop except for 1/150. So that did not explain the over-exposure I observed.

I decided to take a further step and attempted to calibrate the f-stops against a known source. I mounted each lens set in the shutter on a lensboard, set the shutter to f/6.3, and metered the ground glass with a spot meter, with the camera aimed at a blank wall and the front standard set for infinity focus. I then used an equivalent-length "modern" lens and adjusted the f-stop until I got an equivalent exposure from the ground glass. From the modern lens I could read the f/stop giving the same reading.

Based on this method (which I am certain some of you will be able to identify flaws in), the B&L RR lens actually has a maximum f/ in this shutter of 6.3, which is how the shutter is marked, and the Kodak Anastigmat has an f/ of 4.7. And these results are what concerns me.

I have seen the B&L RR lenses mounted in ball bearing shutters with the US f/ markings of f/4 as the max and I know that that system is about 2-3 stops different from the modern f/stop scale. So, the RR result is not surprising. The Kodak Anastigmat lens is marked f/6.3, and since it was mounted in this shutter originally, that would make sense - - both the lens and the shutter were marked f/6.3. But then how is it possible to get a GG reading equivalent to f/4.7 from an equivalent focal length lens focused at the same point? When I got this result, I repeated my set-up and measurement several times to be sure.

Of course, I am going to confirm what I measured by taking test shots, but I only can get out to shoot once every few weeks and I like to make the best of that time, by working out things here at home when I can.

Does anyone have any ideas? Is my testing strategy all wrong? I appreciate any insight from those of you who stuck it out reading all the way to the end. Thanks.

Interesthing: I have a RR lens off a No2-c autographic- kodak Jr" which is with a ball bearing shutter,So you state the following:[You can use one element from the Rapid Rectilinear as a fine 8x10/4x5 ~300mm lens. (Did you know that?)] ok interesting statement but which lens do you remove to make it a 300mm lens???
I also have a kodak anastigmat F7.7 lens which I got with the other lens to be used on my Pony Premo #6 just to play around with: thanks for your time:

I am attaching a photo taken by me with a B&L Rapid Rectilinear removed from a trashed Kodak folding roll film camera, and mounted for my Super Graphic. An old bridge in Mayes County, Oklahoma. F32, 1/25 sec. Forte 200 b/w film, HC-110b.

I've found that some older lenses have the f-stops marked as if the physical aperture was used instead of the virtual aperture. Checking the real (projected) virtual aperture is often a good idea!

Remember that when these lenses were made photographic materials were inconsistent enough that even a full stop difference would go unnoticed.

US apertures have been mentioned before, but it seems it's time for another list:

US 64 = f:32
US 32 = f:22
US 16 = f:16
US 8 = f:11
US 4 = f:8

Note that the US aperture value doubles for each stop. There were several other systems in use, so the assumption that any lens with these numbers on it must be marked in US is not valid. It could also be Stolze, or Rudolph, or "French system", or "Arbitrary units", or ...