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    How does the AstraIIIb split mirror work?
    From: Jim Thompson
    Date: 2004 Apr 22, 10:25 -0300

    I understand the basic principle of a split mirror, but so far I have only
    used a whole horizon mirror.  I just got a split mirror from Celestaire, and
    I've been busy getting used to it.
    In the 3.5 x 40 telescope I can see the mirror on the right, and the horizon
    on the left.  But why does the body's image swing all the way across the
    circular view?  That's great, but somehow I expected it to stop when it
    reached the left edge of the mirror.  The body's image is brighter on the
    right side than the left, obviously because the mirror is on the right.
    In the 6 x 30 telescope I cannot see the mirror on the right.  The view
    looks even more like the whole horizon mirror, except that the mirror
    appears in the far right of the image as a smudge, which I can eliminate by
    carefully holding the sextant in a certain angle.  The Body's image appears
    in the whole circular field of view, even more like the whole horizon
    How does the body appear across the entire circular view of the telescopes
    when using a split mirror?
    Jim Thompson
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