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    Re: How does the AstraIIIb split mirror work?
    From: Trevor Kenchington
    Date: 2004 Apr 25, 14:05 +0000

    I would suggest that the combination of your eye and your sextant
    telescope are focused on infinity, whereas Jim's is focused on his
    horizon mirror. That would explain the difference between what each of
    you sees.
    It may be a matter of the focus control on your telescopes, the depths
    of field of your 'scopes, or one of Jim's eyes being better at focusing
    on close objects. Most likely, all three factors are in play.
    Trevor Kenchington
    You wrote:
    >>I repeated the experiment, this time blocking the horizon mirror's
    >>clear window from the front.  Not surprisingly I guess, for all 3
    >>sighting devices (sight tube, 4.5x30 and 6x40 telescopes) I only saw
    >>the index mirror's image in the right half of the field of view, and
    >>it stopped sharply at the center of the field of view where the
    >>vertical edge of the mirror ended.
    > This is surprising. When I block my horizon mirror's clear window from
    > the front (leaving the mirrored half unblocked), I see the index mirror's
    > image across the entire field of view with a 5x36 scope.
    Trevor J. Kenchington PhD                         Gadus@iStar.ca
    Gadus Associates,                                 Office(902) 889-9250
    R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
    Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555
                         Science Serving the Fisheries

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