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2868Re: Evaluating my "new" Megrez

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  • spacephotographer
    Oct 1, 2004
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      Is your star test similar to what I posted in the photo section?

      Look in Ignacio Alberto folder ( There is another Ignacio )

      I still don´t know how bad is my problem but I think you should
      perform some real tests like observing the moon or saturn. If the
      views are fine then you dont have a problem. You have to compare the
      view with a similar telescope. ( 70 to 90mm ) Don´t try to compare to
      a larger telescope because the performance would not be better even
      with perfect optics.

      Having diffraction rings in only one side of focus is a clear symptom
      of spherical aberration, however all refractors have this problem to
      some extent. If the error is really bad ( 1 wave or more ) you won´t
      be able to focus on saturn or have 100X-120X on the moon.

      If it is 0.2 to 0.3 wave error you also have the bad star test but
      the optics are still in the acceptable region and is very difficult
      to see any difference.


      --- In William-Optics@yahoogroups.com, "gordogower2000" <ggower@t...>
      > I spent some time doing some casual star gazing tonight with
      my "new"
      > Megrez with its brand new WO diagonal.
      > I find that star images inside of focus have a decent set of rings,
      > but outside of focus, star images are just blobs of light. Can
      > someone tell me what that means?
      > I should add that a former owner has placed a tinfoil spacer
      > the lens elements apparently to relieve some astigmatism (so I was
      > told by the prev. owner,and I can see the tinfoil).
      > I am not a star test expert. Can someone advise?
      > Thanks,
      > Gordon Gower
      > Tucson
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