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Re: TEC/TMB/AP eyepieces

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  • tommack7882 <tommack@pcisys.net>
    ... ratio ... image ... ratio, ... and ... Orthos will add a little undercorrection to a fast null corrected lens. The amount of undercorrection is very small
    Message 1 of 21 , Feb 1, 2003
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      --- In tec-scopes@yahoogroups.com, "vahe352 <vahe@f...>" <vahe@f...>
      wrote:
      > > Actually Vahe, the Zeiss Abbe orthos which Yuri preferred for
      > > contrast were optimally designed for f/10 systems, but do not
      > > suffer terribly with moderate departures from this system
      > > requirement.
      >
      > The question is what is moderate departure. It is my understanding
      > that the 1.25" Abbe's were initially intended for the Zeiss APQ
      > series refractors, ranging from 4 to 6" in aperture and with F
      ratio
      > of f/6, f/8 and f/10. To me moderate departure is somewhere around
      > f/8, below that you should see problems near the edge of the field.
      > Of course since these babies are primarily intended for planetary
      > work, and considering the planet's size as it appears in the
      > eyepiece, once the planet is centered you should get acceptable
      image
      > from f/6 on up.
      > My fastest scope is f/9 and Abbe's work just fine with that F
      ratio,
      > in my f/20 scope if the planet is moved midway between the center
      and
      > the edge the image remains crisp and sharp, with the f/9 Abbe's do
      > not behave that well , does that tell you something?
      >
      > Thanks,
      > Vahe

      Orthos will add a little undercorrection to a fast null corrected
      lens. The amount of undercorrection is very small but there none the
      less.

      Cheers,
      Tom Mack
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