Rapid Rectilinear Spacing

[Chauncey Walden]

I happened to run across the unmarked front and rear mounted cells of a large old lens and, what the heck, for $12.50 including the brass shade, I didn't even argue over the asking price. A cursory examination makes me guess that it was about an 18 inch f/8ish RR. Does anyone have one mounted (Jim? Ole?) who could tell me the spacing? Or, would anyone have a formula or even a guess as to the proper spacing range before I go into barrel making mode?

[Wimpler]

just from experience with similar lenses I'd say about 70mm. You would have to measure the exact same lens to make sure.

[Ernest Purdum]

Since they are unmarked, how about sticking the cells in some sort of plastic plumbing tube temporarily and see what results? Not very scientific, but it could vbe interesting.

[Uli Mayer]

The formula is here (equation 1.16 or 1.17):
http://www.mellesgriot.com/pdf/001.8-1.10.pdf

[Chauncey Walden]

Uli, I ran the numbers and, Wimpler, 70mm is as good as anything. Minor variances just change the combined focal length a little. I made a barrel out of a cardboard mailing tube and mounted it in an extra board I had. I just tested it on the camera and it is now a 19 ½ inch f/8 lens. Looks pretty good on the ground glass with just a little "glow". I'll give it a try wide open then decide if I want to work out some stops for it. Thanks for the input.

[Chauncey Walden]

Oh, and Ernest, I checked out the plastic plumbing tubes and, as the lens threads are a bit larger than 3 inches, I thought it would be easier to rough out a 3 inch mailing tube than the heavy plastic.