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    Inverting scope. Was: Perpendicularity check
    From: Alexandre Eremenko
    Date: 2004 Sep 22, 23:16 -0500

    On Wed, 22 Sep 2004, Fred Hebard wrote:
    > From my experience with microscopes, the reticule is usually,
    > a glass disk with the cross hairs or parallel lines inscribed on
    > it.  Frequently, there are two threaded rings
    No, this one is much less sophisticated.
    The cross hairs are just ordinary real wires rigidly attached
    to the tube. The whole scope has only one adjustment parameter:
    you can make the tube shorter or longer. That's it.
    More precisely, the scope consists of two tubes which fit
    tightly one inside another. The thiner tube has the objective lens
    rigidly attached in front, and the crossbar hair (wires)
    attached to the other (back) end. The thicker tube has the eyepiece
    rigidly attached to its back end and the front end is open.
    The back of the objective tube is inserted in the front end
    of the eyepiece tube. That's all.
    To focus you hold this assembly with two hands and move
    one tube with respect to another.
    So this is the most primitive "Kepler telescope" you can imagine.
    (As a child, I made such telescope myself, but never used it
    because it was inferior to my binocular, despite the higher
    magnification power and larger lens diameter).
    The stars look surrounded by round spots of light, like hairs
    of light sticking from the star;
    these spots are excentric unless the star and your eye are
    exactly on the optical axis, in which case they are perfectly
    round with the star in the center.
    (I thought this is called "spherical
    aberration, is not it?)
    > Bruce Stark discusses centering the contact
    His book is on my shopping list, right after the Almanach:-)

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