Help with vintage Schulze & Billerbeck lens

[jodys]

<p>Help! I just bought a selection of old lens elements and gear, and to my surprise I found 2 beautiful matching elements marked: Euryplan-Anastigmat Series I f4.5 6", Sold by A.E. Staley & Co, London. From the Vademecum, I find the lens is made by Schulze & Billerbeck, and is actually an important 6-element design that was a precursor to most modern lenses. The specs (from elsewhere): 80 degree field, 6 elements in 4 groups (external crown, others in the series were wider and had an internal crown element).</p>

<p>My problem: I wish to manufacture a brass tube with Waterhouse stops to mount these. I have the machining skills to do this, what I don't have is the overall dimensions of the lens, or if you will the distance separating the 2 elements I have. All I have to date is a photo of the 8-1/4" from the VM, shown below. I do have basic math skills, I can blow this up, print it out, and apply some basic trigonometry to come up with a figure. But I don't know if the 8-1/4 has the same proportions as the 6", and I won't be able to get a measurement within the tolerances I should be using to build this.</p>

<p>Does anyone have such a lens they could measure for me, or access to better data and specs on these?</p>

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[john_shriver]

<p>One approach would be to setup some sort of simple optical bench, and find that spacing that makes the focal length correct. Presuming the lens is symmetric, you know where the focal point is. Then you just need a collimated (or distant) light source, and a screen to put at the focal length from the focal point.</p>

[jodys]

<blockquote>

<p>One approach would be to setup some sort of simple optical bench, and find that spacing that makes the focal length correct...</p>

</blockquote>

<p>I was wondering if there was some optical test I could use to do this. But with vintage lenses, how often is a '6-inch' focal length exactly 6 inches? I have a number of process lenses off printing cameras that are much more recent, even, that all have hand-scratched notes in the sides with focal lengths and apertures. A 210mm process lens would test at 217mm, and f9.3 instead of f8 (just one example I happen to own, a Staeble-Ultragon). So I was thinking of using the point light source I use to focus at night, which is basically a cheapo LED flashlight, which I use by pointing at the camera and focusing until I can distinguish the individual LEDS on the ground glass. I thought I might be able to determine spacing for these elements by experimenting with 2 of these, one in the center and one at the edge of the image circle, and adjust spacing until I get the best edge with an in-focus center.</p>

[john_shriver]

<p>That's an interesting approach, trying to adjust for minimum curvature of field. Of course, that's different at each aperture, which is why it drives people mad.<br>

Maybe S. K. Grimes already has the right dimensions on file?</p>