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    Re: Dioptric correction
    From: Frank Reed
    Date: 2013 Jan 21, 12:36 -0800

    Norm, use either eye. You can focus the sextant scope for normal correction just as you would with an astronomical telescope. And also like an astronomical telescope, if one is astigmatic, re-focusing can help only along one axis. Though it can be inconvenient, you can wear eyeglasses while using a sextant, too.

    You wrote:
    "My collection of telescope tubes, lenses, etc. is in quite a state of disarray to the extent that I really can't seem to bring any combination into focus without extending eyepiece or objective beyond it's threads. I did notice that I have one tube that seems to telescope into the other tubes, but can't get the right combo, as two of the tubes have reticles in them."

    First, take your time. Don't break anything! If the reticles still have the threads, that adds value. Second, start breaking things. :-) I acquired a vernier sextant from the 1890s some years ago, and it took me quite a while to get a working scope from the parts available. I strongly suspect that the bits of the various scopes had been put back together by someone decades earlier who did not see them as optical instruments and instead saw them as attractive artifacts. So you should disassemble the scopes as best you can down to the components that are supposed to be separated and then figure out their optical properties. You can then put them back together properly. If you have two telescopes that can't be focused, they probably have their oculars swapped. Also note that some of the old parts that are supposed to be movable can be frozen in place by a little corrosion. Sometimes separate tubes appear to be one thanks to a patina that shades smoothly across the junction between them. Get out a magnifier and see if you can figure out what's supposed to move and what isn't. And bear in mind that old sextants were built with the principle that everything could be adjusted by the end user. If it looks like it was meant to move, it probably can move. You may need to apply some serious torque to get two stuck tubes to unscrew. That's my two cents. Bill Morris, as always, is the real expert on this sort of refurbishment.

    -FER


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