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  1. #1
    Edward's Avatar
    Edward Guest

    Default Interferograms for Four High Quality Telescopes and Two Commercial Telescopes



    Some of you might be might be interested in photos and a brief analysis
    added to Roland Christen's essays:
    http://voltaire.csun.edu/roland/interfer.html

    Ed T.



  2. #2
    George Normandin's Avatar
    George Normandin Guest

    Default Interferograms for Four High Quality Telescopes and Two Commercial Telescopes


    "Edward" <> wrote


    Ed,

    Interesting stuff!

    I recently purchased a used Obsession 20-inch Newt. The Torus mirror had
    been re-figured at the request of the owner, even though the specs show it
    to be "OK", but not "spectacular". Torus now posts on their website
    interferograms of each mirror and re-figured mirror that they do. On the
    mirror I have, the re-figured mirror is not as good peak-to-valley, but it
    has a better RMS and Strehl ratio. In fact it is better than the figures on
    my 10-inch RC Cass, and a 20-inch RC Cass that I use a lot. Torus also
    provides figures that are the average of 20 interferogram tests, plus a
    Ronchi grating image. They average results of many tests because they claim
    that there is too much variation between test runs. They were having
    problems with producing a few turned-down edges and missing them with just
    an interferogram test, so they concluded that they also had to do the Ronchi
    test as the best way to detect a turned edge.

    George Normandin



 

 

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