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    Re: Index checks with laser and without
    From: Bill B
    Date: 2007 Jan 04, 17:49 -0500

    Alex wrote
    
    > But it does not help me much with stars index checks.
    > The stars I see are not exactly points, and brighter
    > ones look bigger. This could be a telescope problem
    > but more likely my vision problem.
    
    Another one of those shower moments....  What I believe we established is
    that the strong defraction spikes we use for measurement using Franks
    IE-check method are caused by the laser beam being split at the horizon
    glass and mirror junction.
    
    I do note, depending on which eye I use, I can get pretty near to a point
    source on the glass or mirror side. Better yet with eyeglasses. It is when I
    move the image to the center to split it that I get the tails and
    distortion.
    
    Is it possible the same effect as the laser spike are at work with a point
    source entering the system? The argument counter to this is that the
    defraction spikes produced by the laser run at right angles to the
    glass/mirror junction.  Therefore a point source should have horizontal
    spikes with the sextant held in its normal position, which would aid in
    aligning the two star images.  Also, my  tails run at 45 degrees down from
    horizontal.
    
    Bill
    
    
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