It's pretty well known that with their 1867 Patent Portrait lenses, Dallmeyer refined and reversed the Petzval's rear air-spaced group. I've heard some other manufacturers later did the same. The Vitax may be one; Wollensak called it "an improved Petzval formula" and "a modification of the Petzval formula", but they may have been referring to the diffusion dial or some other refinement.
Does anyone know of other Petzval's that were designed to have their rear group reversed, as Dallmeyer did?
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