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    Re: Metal versus plastic or better telescope?
    From: Alexandre Eremenko
    Date: 2012 Mar 28, 00:36 -0400

    Thanks!
    Looks reasonable. It did not occur to me that there is no need
    to attach the scope:-)
    If you have a horizon or a roof far enough.
    
    
    Alex.
    
    On Tue, 27 Mar 2012, Frank Reed wrote:
    
    >
    > Alex, you wrote:
    > "Could you give more detail? What 30x scope, and how do you attach it to a
    > sextant?"
    >
    > It's amazingly simple (considering all the energy we devoted to this topic 
    over the years). You just place your sextant on its side on a table. Shim it 
    up so that you can see centered in the field of view some distant sharp line 
    like a tower five miles or more away from you. Then remove the sextant 
    telescope. Get an ordinary spotting scope with magnification generally in the 
    range of 30x to 40x. Place the spotting scope on a tripod (or on some support 
    on the table) and place it in line with the usual location of the sextant's 
    telescope. There's no need to attach it. Then you look through and because of 
    the magnification the slightest motion of the micrometer yields a visible 
    shift between the direct and reflected image of your distant target. You can 
    now easily experiment with the various factors that affect index correction. 
    For example, you can measure IC for clockwise and counter-clockwise motions 
    of the micrometer drum. Again, with a decent sextant, the repeatability is 
    excellent. Any brand of spotting scope with reasonable optical quality will 
    serve. I bought one on eBay for around $50. You could even use a backyard 
    astronomical telescope, but there are some issues that arise. Besides a 
    spotting scope is a nice tool to have around.
    >
    > -FER
    >
    >
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