ULF Lens

I just picked up A 25" rapid rectilinear. The aperture scale is one I've not seen before. Wide open it is 7.5 then 10...15....25....50....100. This will take a little getting use to. Has anyone used or seen this type of aperture scale before? Thanks, Robert

Robert,

I am no lens expert, but I dug up a comparative table of Diaphragm numbers that I someone posted a couple of years ago - I believe on the Large Format Photographers Forum. It shows several diaphram numbering systems and how they relate to the traditional F stops that we are used to working with. The chart lists a heading called "Dallmeyer" that appears to closely relate to what you have listed. Here are your numbers and their apparent "normal" f stop equals:

7.5 = F4.5, 10 = 6.8, 15 = f11, 25 = F16, 50 = F32, and 100 = F64.

These numbers are close comparisons (not exactly equal but close enough) but appear to relate to what you have. I would caution that you also get confirmation from the experts here that what I have told you is correct.

I too have a lens that has baffling F stop numbers on it - it is a 135 mm Liesegang Parastigmat series II 1:4.5. I believe that it might be an enlarging lens although it doesn't really look like it is. However, the stop numbers on mine don't relate to any of the system comparisons in the chart that I have.

RobertP said:

I just picked up A 25" rapid rectilinear. The aperture scale is one I've not seen before. Wide open it is 7.5 then 10...15....25....50....100. This will take a little getting use to. Has anyone used or seen this type of aperture scale before? Thanks, Robert

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The original classic Rapid Rectilinear has a maximum aperture of about f/8. Your aperture system might be in the old U. S. system where 8 = f/11, 16 = f/16. 32 = f/22, 64 = f/32, and 128 = f/45. Photography with your lens might be simpler if you tape over the aperture scale and recalibrate it in familiar f/ stops.

Jim Jones makes an excellent suggestion. I calibrated an old Imagon with no aperture scale. First I placed my camera over a light table with a light meter probe at the center of the ground glass, and mounted a proven 300mm lens. As I closed the aperture, I recorded the light meter readings at specific f-stops. Next I mounted the Imagon, and marked the position where the light meter readings were the same as known f-stops. Exposing some test film, the results were within 1/3 stop.

I used lenses of the same focal length, but I don’t think it would make much difference, as long as the light meter probe was in the center of the gg.

It's not likely to be US, it's not likely to be any of the many German systems, and it's not likely to be "relative illumination".

It's likely to be one of the many proprietary scales, although it could actually be real f-stops. F:7.5 is a quite likely maximum aperture for a RR! 10 and 15 fit in well, one and two stos down. Then the jump to 25, 50 and 100 don't really make sense - but lots of old lenses have scales that don't really make sense now. Try measuring the opening at the different markings, that might give a clue.

Thank you all for your input. Ole, It is indeed a Dallmeyer Rapid Rectilinilear 18x16. I may just have to have Grimes make a new aperture scale. I've never heard of an f4.5 Rapid Rectilinear so these could, like you say, be the actual f stops. The lens is in such nice condition I'm thinking of front mounting a Packard to it.This just means I'll have more money in a new aperture scale and shutter than I will have in the lens. But that is not uncommon. I'll let you know what Adam says about it at Grimes. Thanks again.

Robert, that lens sounded familiar.

But my 18x16 RR is a Ross, and has Waterhouse stops.

However I also have a Lancaster 12x10" Patent Rectigraph, with similar aperture markings: 10, 20, 30, 40 and 50. But there's a second scale on that one, marked "Time". 1 is at "10", 2 is midway between "10" and "20", 4 at "20", 8 at "30", 16 at "40" and 25 at "50". In this case I've determined that the markings really are F-stops, and the lens really is a 13" f:10 Rapid Rectilinear!

Another lens which starts at "4" is a Petzval, so it really is f:3.5 (there's a little distance between wide open and the first marking. Size and weight are unmistakable!