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  1. #1
    Uncle Bob's Avatar
    Uncle Bob Guest

    Default OWL Telescope structure




    I'm looking at the BBC website, and they have a story about larger
    telescopes (mankind has aperture fever) coming on-line at various future
    dates.

    One telescope they mention, and provide an artist's rendition to
    illustrate, is the OverWhelmingly Large telescope. A link to the
    website is here:

    http://www.eso.org/projects/owl/index_3.html

    If you look at the structure, you can see there is a latticework
    secondary support extending from the edge of the mirror assembly to the
    secondary holder area.

    Isn't this kind of arrangement going to give the telescope very weird
    diffraction spikes, to say the least?

    Looks like an awful lot of stuff thrust into the light path. Is this
    the actual design they're considering?

    Uncle Bob

  2. #2
    Pat Wallace's Avatar
    Pat Wallace Guest

    Default OWL Telescope structure

    In article <42595776$0$6754$9a6e19ea@unlimited.newshosting.co m>,
    Uncle Bob <realonespam@bogusnet.net> wrote:

    There's a picture of the point-spread function on p4 (Fig. 2) of:

    http://www.obs-hp.fr/~arnold/publi_t...20710final.pdf

    The secondary supports look a lot more alarming seen from the side than
    when projected onto the pupil. But remember also that both the primary
    and the secondary are made of hexagonal segments, and the gaps mean more
    diffraction. There are also missing segments. For a picture of the
    pupil, see p7 (Fig 6) of:

    http://www.eso.org/projects/owl/File...imulations.pdf


    Patrick Wallace
    __________________________________________________ __________________________

  3. #3
    Mark Gingrich's Avatar
    Mark Gingrich Guest

    Default OWL Telescope structure

    Uncle Bob reported:



    The Kecks' diffraction pattern is similarly bizarre. In addition to the
    familiar spikes caused by the four-vane spider, there's added weirdness
    owing to the hexagonal primary mirror segments not sitting flush against
    one another. The effect can be duplicated by placing a "chicken wire"
    screen at the entrance aperture of your own 'scope.

    I've seen more than one technical paper in SPIE publications devoted
    solely to a description of the Keck diffraction pattern. 'Tis necessary
    to quantify this precisely so that image processing can remove the
    artifacts.

    --
    ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
    Mark Gingrich grinch@rahul.net San Leandro, California

  4. #4
    Uncle Bob's Avatar
    Uncle Bob Guest

    Default OWL Telescope structure

    Mark Gingrich wrote:



    Those SPIE pubs are a bit pricey for me, but thanks for sharing.

    I'm out looking for some chicken wire. I want "Keck-like Performance".
    Can I call it a Ritchey-Chretien, too?

    ;-P

    Uncle Bob

  5. #5
    Ralph Hertle's Avatar
    Ralph Hertle Guest

    Default OWL Telescope structure

    Uncle Bob wrote:


    ............................

    Uncle Bob.

    I have tears in my eyes from laughter.


    Turn off the phones. There are days when you may hope to be in Bali. A
    client of mine recently went to South America.



    Ralph Hertle



  6. #6
    Maurice Gavin's Avatar
    Maurice Gavin Guest

    Default OWL Telescope structure

    On Sun, 10 Apr 2005 09:42:28 -0700, Uncle Bob
    <realonespam@bogusnet.net> wrote:


    All mosaic mirror systems [even Keck] produce diffraction patterns
    from each mirror segment edge - typically three from a hexagonal
    mirror. The structure shadow may be in the gaps between mirrors.

 

 

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