Lens: Rectilinear or newer?

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Charles Twist
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Lens: Rectilinear or newer?

Post by Charles Twist » Wed Jan 18, 2012 2:19 pm Etc/GMT-1+01:00

I am the happy owner of a Rodenstock Anastignar, about which there seems to be precious little information online or in the Vade-me-cum. I am trying to work out if it's a rapid rectilinear or something more sophisticated designed in the 1890's. It's a brass tube with a lens group at each end. So it's not a triplet or any of its derivatives or a Tessar. I am trying to work out if the two lens groups are composed of two or more elements. I have vague recollections that you can look for the number of apparent images of a spot bulb in the lens group and there'll be one per refractive index change. So 3 for a rectilinear and 4 for Goerz-style anastigmat. Is that right?

Anybody any knowledge about the lens?


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Susie Frith
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Joined: Tue Jul 26, 2011 5:28 pm Etc/GMT-1+01:00

Re: Lens: Rectilinear or newer?

Post by Susie Frith » Mon Feb 13, 2012 7:10 pm Etc/GMT-1+01:00

Hi Charles,

I would assume that as the name has the root Anastig- then the lens will be an anastigmat and therefore not in the Rapid Rectilinear family, and would date from after 1890.

The Tessar has a un-cemented pair in front of the iris and a cemented pair behind. If it is pre-1920 then it could be a modified Tessar (the patents didn't run out until then) the usual one being to use a cemented triplet instead of the doublet.

An uncoated air-glass surface will yeild a bright reflection, but a cemented surface gives a dull one. If there is an air space and the reflections move the same way, then the two surfaces are both either convex or concave. If they go opposite directions, then one surface is convex and the other concave. If the lens will unscrew from the barrel then inspect each half individually.

The Goerz Dagor is a symetrical lens with three elements each, so both halves will show two dull reflections: both surfaces of the inner element are concave in the Goerz, or convex if a reversed Dagor....(By the way, in the first three years of production Goerz sold over 30,000 Dagors - or Double Anastigmat GOeRz as it was before 1904.

Anyway, the upshot is that I would be pretty sure that it is an astigmat, given its name!


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