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    Re: How does the AstraIIIb split mirror work?
    From: Jim Thompson
    Date: 2004 Apr 24, 09:04 -0300

    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.
    For what it's worth, I again blocked the clear window from behind and
    studied the slightly dimmer index mirror's image that showed past the center
    line in the left half of the field of view.  I could only perceive a single
    image reflecting from the clear window, but I don't know how precise that
    would be.  I don't know whether I could pick up two images (one from the
    front of the horizon glass and one from the back) with the resolution of my
    biophysical optics, if in fact there are two images spaced very slightly
    apart vertically in the left field of view.  I was looking at a series of
    horizontal black electric lines against blue sky about 200 yards away, using
    the 6x30 telescope.
    Jim Thompson
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