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Thread: coronograph

  1. #1
    Valerio Cammelli's Avatar
    Valerio Cammelli Guest

    Default coronograph




    I am making a prominence viewer (lyot coronograph)
    but i esitate betwin two project :
    1) to insert the baffles betwin the objective lens and the
    first focus (cone) to break up the internal reflection.
    2) no baffles but internal black paint .

    Does the baffles can cause fresnel's diffraction ?

    thanks ,Valerio

  2. #2
    Bob May's Avatar
    Bob May Guest

    Default coronograph

    There is only one aperture stop in a telescope design and it will always
    produce the diffraction. Put that stop anywhere you feel the need - the
    objective is usually where it is. Baffles are normally out of the light
    path and won't produce any effects on the light other than to baffle
    off-axis light from the viewing of the image.

    --
    Yeppie, Bush is such an idiot that He usually outwits
    everybody else. How dumb!



  3. #3
    Dan Mckenna's Avatar
    Dan Mckenna Guest

    Default coronograph

    Valerio Cammelli wrote:

    Valerio,

    Be very careful with your development of a chronograph !

    One bump of the telescope mount and you are looking at the unfiltered sun.

    Also be aware that chronograph sites usually are in clean air at as high
    an altitude as practical to reduce atmospheric scattering.

    Safe viewing
    dan

  4. #4
    Ashbury's Avatar
    Ashbury Guest

    Default coronograph


    "Bob May" <bobmay@nethere.com> wrote in message
    news:ioKdnd_jaPKLVbfYnZ2dnUVZ_sqdnZ2d@nethere.com. ..


    How is the C-graph made?



  5. #5
    Bob May's Avatar
    Bob May Guest

    Default coronograph

    C-graphs are made by putting an obstruction into the light path at the focal
    plane and viewing that focal plane with the sun obstructed out of the way.

    --
    Yeppie, Bush is such an idiot that He usually outwits
    everybody else. How dumb!



  6. #6
    Martin Brown's Avatar
    Martin Brown Guest

    Default coronograph


    Dan Mckenna wrote:

    Provided the baffles are just outside the light cone they only stop
    internally scattered light from reaching the focal plane. You still
    want everything internally as matt black as possible.

    Unclear whether he means a true white light coronograph, or a
    prominence coronograph like the Baader one using an occulting disk to
    hide the photosphere with H-alpha filter & ERF. Either way you cannot
    afford to make any mistakes with optics pointed at the sun.

    It is a lot easier to make a prominence viewer using a modern narrow
    band H-alpha filter and an ERF (although they are not components to
    make at home). I have a drain pipe H-alpha prominence scope using a
    Chinese airspaced achromat and an early Coronado 2A filter.

    And to get anything like a white light coronograph working needs
    extremely careful design and exceptionally well crafted high quality
    ultra transparent glass glass optics. All narrow angle scattered light
    otherwise ends up spoiling the view (as does any dust in the air).


    ISTR there is a minimum altitude below which the atmospheric dust and
    humidity spoils the view for a true white light coronagraph for most of
    the time.

    Regards,
    Martin Brown


  7. #7
    Valerio Cammelli's Avatar
    Valerio Cammelli Guest

    Default coronograph

    On Mon, 09 Oct 2006 17:40:51 -0700, Dan Mckenna
    <dmckenna@as.arizona.edu> wrote:


    Thanks, but my instrument is a prominence viewer with a
    interference filter FWHM 1 nm , i think this is safe.
    Valerio

 

 

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