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Re: [woodandbrass] William H. Walker posting

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  • Richard Knoppow
    ... From: John Rushton To: Sent: Monday, July 30, 2012 2:59 PM Subject: RE: [woodandbrass]
    Message 1 of 4 , Jul 30, 2012
      ----- Original Message -----
      From: "John Rushton" <jcr_cameras@...>
      To: <woodandbrass@yahoogroups.com>
      Sent: Monday, July 30, 2012 2:59 PM
      Subject: RE: [woodandbrass] William H. Walker posting

      > Hi Dan,
      > Thank you for your excellent article on Heliar lenses.
      > Was it the Heliar lens or the Universal Heliar lens that
      > the Japanese
      > emperor insisted upon? Your article indicates the Heliar
      > but I had always
      > understood it to be the Universal Heliar.
      > Best Wishes,
      > John

      Kingslake's article on the Heliar is quite interesting
      although short. He says that Hans Harting tried four design
      variations of the original Heliar. The first was
      symmetrical but the patent data indicates it suffered from
      astigmatism and severe coma. He next tried making the lens
      asymmetrical which improved its Petzval sum and astigmatism
      but the coma remained and the distortion was worse. It was
      no better than a triplet. Hartings next variation was to
      reverse the order of powers of the front and rear cemented
      elements so that the convex lenses faced outward. This is
      the lens originally called the Dynar but the name was
      changed to Heliar. It was superior to the second Heliar
      design although with greater astigmatism. The final
      variation was to have the front element with the concave
      element facing outward and the rear with the convex element
      facing outward. This lens was sold as the Oxyn for process
      work. Evidently Voigtlander continued to adjust the design
      of the Heliar. While some of these lenses have a reputation
      for being somewhat soft focus when wide open they seem to be
      quite sharp when stopped down a bit. The series of lenses
      designed by Fred Altman of Kodak are similar to the Heliar
      but Altman states in his patent that the additional elements
      are to correct the rim rays and increase speed rather than
      to improve chromatic aberration. This suggests that he
      thought that the purpose in the Voigtlander designs.
      Altman's lenses have very high performance and excellent
      chromatic correction. Kodak used the Ektar name for lenses
      which were suitable for color photography and made such in
      order to promote the use of color film. The Commercial
      Ektar series, and its predecessor the Eastman Ektar are
      nearly apochromatic having excellent correction for lateral
      color which is somewhat unusual for a Tessar type lens. The
      difference between the Eastman Ektar and Kodak Commercial
      Ektar is the coating. In the earlier Eastman Ektar a soft
      coating is applied to inner surfaces which are protected,
      the Commercial Ektar has hard coatings on all surfaces.
      The Voigtlander Color Skopar, a Tessar type lens, is
      also supposed to be nearly apochromatic and I suspect the
      Color Heliar is also but have no definite information. Its
      very likely that the post-1945 versions of these lenses were
      designed to make use of rare-earth glasses, very certainly
      the Kodak Ektars were since the glass types were developed
      commercially at Kodak from the original National Bureau of
      Standards research.
      Its interesting that this basic form of lens seems to
      have been little explored by designers. Other than the
      Kodak series only the Dallmeyer Pentac is of a similar type.
      I think perhaps other basic designs offered more potential.
      Certainly, air spaced lenses of all sorts obsoleted many
      cemented types once effective and durable lens coatings
      became available.

      (1) _A History of the Photographic Lens_ Rudolf Kingslake
      1989, The Academic Press
      (2) _Handbook of Photography_ Keith Henny and Beverly Dudley
      1939, Whittlesey House-- McGraw-Hill Book Co. Chapter III,
      "The Development of the Photographic Objective" by Rudolf
      A note: Kingslake was a prolific writer; anything he
      wrote is worth reading.

      Richard Knoppow
      Los Angeles
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