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    Re: Mirror problem
    From: Alexandre Eremenko
    Date: 2006 May 5, 14:09 -0400

    Dear George,
    Thank you very much for your most interesting message.
    (Someone already complained on the list that your
    messages are hard to read because they do not contain
    line breaks. With my mail program I read then easily,
    but to REPLY a long message from you is a real
    pain, exactly for the same reason: there are no line breaks,
    your paragraphs consist of single line of text each).
    Back to your message:
    Your explanation of the index mirror bending
    is very clear. I checked my sextant: it has ONE
    adjusting skrew and three springs. One of the springs
    is opposite to the adjusting screw. The whole configuration
    looks like this:      :+
    where the dots and the plus sign mean the springs, and the
    adjusting screw is behind the + sign.
    I assume that the sextant is hold with its frame plane vertical.
    So the design seems sound to me.
    > The complaint that Alex makes, about a doubled star image,
    > with a weaker displaced image or tail as seen in the mirrors,
    I would not call it "double". I would rather say it is
    somewhat "blurred", and of irregular shape. It LOOKS
    like an image in a low quality scope.
    But the OTHER image, through the horizon glass looks
    like an image in a good quality scope.
    I can certainly test the spare mirror that I have.
    And your idea of putting a diaphragm on the mirror,
    decreasing its effective size is great.
    If the reason is the mirror deformation, then the diaphragm
    should evidently decrease it.
    It is probably also possible to design an experiment that
    will show which mirror is really responsible
    for my problem: I am just
    thinking of fixing the sextant somehow and looking
    into the index mirror through the detached telescope
    (which I can hold in my hand) under different angles.
    (My main technical problem with all such experiments
    is the shaking of the wooden balcony floor as I move; this
    also almost prevents me from using the art horizon.
    But I will invent something to overcome this:-)
    BTW, do you think it safe for the eye to use a laser pointer
    in the experiments? Together with Sun filters, of course:-)
    It looks much less bright than the Sun.

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