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  1. #1
    André P.'s Avatar
    André P. Guest

    Default Eyepiece exit pupil question



    Hi there !

    For fun, hi checked the exit pupil of some of my eyepiece. I check this in
    looking the eye-lens with holding the eyepiece at the end of my arm.

    For some eyepiece the exit pupil is about 6 to 12 mm, (Speers Waler 7mm and
    18mm, Nagler 12mm type 4) but for other eyepiece the exit pupil seems to be as
    large as the eye-lens (Speer Walers 30mm, Omcom Erfle 52mm, Omcon Plossl 40mm).

    What is that ?

    Thanks and clear sky !



  2. #2
    Jon Isaacs's Avatar
    Jon Isaacs Guest

    Default Eyepiece exit pupil question

    >Hi there !

    The exit pupil is a function of the focal ratio of the scope being used and the
    focal length of the eyepiece. Need to use a scope.

    I think what you are looking at is the field stop which sets the Apparent Field
    of View of the scope. The AFOV is approximately the field stop diameter
    divided by the focal length of the eyepiece converted then from radians to
    degrees. AFOV=(Field stop/focal length)*57.3 degrees

    Thus the short focal length eyepieces have smaller diameter field stops and
    when used without a scope an apparently smaller "exit pupil."

    jon



  3. #3
    Michael A. Covington's Avatar
    Michael A. Covington Guest

    Default Eyepiece exit pupil question


    "André P." <gritch@netcourrier.com> wrote in message
    news:r0yvb.18399$iT4.2180723@news20.bellglobal.com ...
    in
    and
    be as
    40mm).

    You are not viewing the exit pupil. The exit pupil exists only when the
    eyepiece is in the telescope.




  4. #4
    André P.'s Avatar
    André P. Guest

    Default Eyepiece exit pupil question

    Jon Isaacs wrote:

    Thanks to you Jon !


  5. #5
    André P.'s Avatar
    André P. Guest

    Default Eyepiece exit pupil question

    Michael A. Covington wrote:


    Thanks Michael !


 

 

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