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24161Re: [tmboptical] Re: TMB 80mm "super" apo

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  • APM-Telescopes Markus Ludes
    Apr 2, 2005
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      Hi Tom,

      I know that what you write below, but in todays world it is to strict term, since if we follow strict terms, there shouldbe no one who call his apo, really apo , from design poinht maybe yes, but from making point no.

      I mean if Zeiss take for themself the right to call here Binoculars super achromat, then LOMO shall have the same permission to call here 80 mm babys, Super - Apo , right ?

      Takahashi, Vixen and others call here douplets Apo , doesnt matter if they say ED or Fluorite, this only indicates what type of glas they using, but this scopes should then not be called apos, right ?

      so we have to allow Lomo the same flexibility to use terms as others have too

      right or wrong ?

      best wishes

      Markus
      ----- Original Message -----
      From: tmboptical
      To: tmboptical@yahoogroups.com
      Sent: Friday, April 01, 2005 7:53 PM
      Subject: [tmboptical] Re: TMB 80mm "super" apo



      --- In tmboptical@yahoogroups.com, "APM-Telescopes Markus Ludes"
      <apm_telescopes@w...> wrote:
      > Tom
      >
      > from where you have the technical specs you use for the Term super
      apo ? To my knowledge a superapo must have 4 crossings ( a normal apo 3
      crossings) , and nothing additional then other apos
      >
      > the 80 mm design exceed the APQ design and have 4 crossings and
      therefore LOMO called them with all rights super apo
      >
      > best wishes
      > Markus

      Markus,

      >From none other than the greatest optical scientist in the 20th century,
      and also the man that came up with the term "Super Apochromat," James
      G. Baker. In his groundbreaking article in Applied Optics, back in
      1963, called "Planetary Telescopes," he outlined why refractors are
      the very best telescopes of any type, for planetary observing, and
      in fact, showed back in the 1940's, that he was the inventor of the
      modern triplet apochromat, where the power element made out of CaF-2
      is in the center, and two crown elements were matched on the outside
      and inside of the triplet, just like TMB, AP, Zeiss, TAK, and TEC
      use today. His design would hold up to the best of today's designs,
      even know it was designed over 65 years ago. It was BK-7/CaF-2/K-10,
      a darn good true triplet apochromat.

      He also used the term Super Apochromat to describe an apochromat,
      that in his own words: "A Superapochromat is superachromatically
      corrected over the full aperture for aplanation."

      This means that for a lens to be a true Superapochromat, it must
      not only have four color crossings, but it must be aplanatic over
      the entire aperture (coma and spherical), which means no sphero-
      chromatism or coma. The reason no lens reaches this level of
      performance, and James Baker talks about this, is because you
      need to put two higher order aspherics on two surfaces of the
      lens, and this would no longer be a lens that could be sold
      in any real numbers, in fact, very few master opticians can
      do this type of figuring, and the costs would be extremely
      high per lens. So much so, no one would buy it.

      I recommend anyone that wants to learn more about the history of
      apo refractors, why apo refractors are as good as they are, the
      many different design types of apo refractors (for planetary use),
      what the requirements are for different levels of refractor
      correction, and what they mean, should either find a copy of his
      article at a University library, or download it off the Internet
      for about $15.00. It is the ultimate statement on why apo refractors
      are the best telescopes, inch for inch.

      Thomas Back






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