Six element dialyte? Why?

This is a dialyte with doublets at each end, or you could call it a "Heliar" with the middle lens split in two. What could the purpose of this design be? Better definition when using it as a convertible, with only the front or rear part? And as a full lens, would it perform like a Heliar on steroids?

Symmetrical design, process lens for conjugates around 1:1

Symmetrical, yes, but the lens is a normal taking lens for plate cameras. It's the 4,5 version of the Polyxentar by Laack, Rathenow.

That seems more of a modification of the tessar, not dialyte, design, but who knows? Another early attempt to control residual aberrations. I looked it up in Kingslake, and the above diagram does not represent what he identifies as one of the Heliar options. Consult Kingslake yourself for the details.

One possibility is that it was an attempt to work around a patent.

Steve Goldstein said:

One possibility is that it was an attempt to work around a patent.

Click to expand...

Heh.. like Gundlach did with their Radar (one of my favorite lenses).

As already mentioned, adding two elements gives the designer more degrees of freedom in the design which, theoretically allows the design to be better corrected than the related four element design and can be a way to avoid infringing upon a prior patent. Given that this design looks very much like a dialyte, I'd guess it performs an awful lot like a dialyte (not a heliar) but with fewer aberrations or less distortion, etc. Of course, it would also likely be more expensive to produce.

BradS said:

As already mentioned, adding two elements gives the designer more degrees of freedom in the design which, theoretically allows the design to be better corrected than the related four element design and can be a way to avoid infringing upon a prior patent. Given that this design looks very much like a dialyte, I'd guess it performs an awful lot like a dialyte (not a heliar) but with fewer aberrations or less distortion, etc. Of course, it would also likely be more expensive to produce.

Click to expand...

Member and lens designer Nodda Duma doesn't think it would perform better than a normal dialyte, not even when used as a convertible. He is probably right since this design didn't catch on. I guess 100 plus years ago it was both calculations and trial and error that gave us the famous lens designs.

Intriguing thing lies in the name. Polyxentar recalls Xenon, Xenar, and Tessar with me. We know that Schneider and TTH have cooperated, see the Opic-Xenon story. Polyxentar designates precisely what it is, many (poly) Tessar to form something near a double-Gauss six-glass design. Symmetry does not harm LF photography, so the lens has at least the potential of wider relative aperture. The Opic was more or less limited to f/2.0 max.

The Polyxentar bears the Goerz Celor within, to some extent. From that most important design the f/1.9 Velostigmat was deducted and the Kodak Ciné Anastigmat of equal speed, the two with glasses in contact in each group but not cemented. One can understand the Celor enhanced by achromats here, a specialty are the two plane surfaces.