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    Re: Lunar Distances with Alex's SNO-T
    From: Frank Reed CT
    Date: 2006 Dec 03, 15:52 -0800

    Bill, you wrote:
    "as well as producing a circle to mount on the eye end of the scope
    with a tiny hole to be sure I am shooting down the center of the
    scope."
    
    Do you need that? I never did anything like that in my tests.
    
    And you wrote:
    "When matching the predetermined mirror distance, the sextant reading
    was just a hair below 0.8' on the arc."
    
    Sounds good. Try this:
    Set the sextant micrometer to 0.0'. Fire up the laser, and carefully
    measure the distance between the dots (lines) at 20 feet distance with
    an ordinary pair of drafting dividers. Record by pressing the divider
    points into an index card. Now set the micrometer to 1.0' and do it
    again. Record the second measurement the same way, but use the same
    indentation in the index card for one point of the dividers. Then
    repeat both measurements at 40 feet. If you do this right, on your card
    you should have one small indentation on the left as the starting point
    for each measurement and then two indentations closely spaced three or
    four inches to the right (from the 20 foot observations). Just below
    those, you'll have another pair of indentations (from the 40 foot
    observations). The spacing between those marks should be almost exactly
    twice the spacing between the upper indentations. That much is obvious,
    but there's more. If the index error is exactly 1.0 minutes, the two
    indentations furthest to the right will be exactly above each other
    (the same distance from the far left indentation on the card), while
    the other pair of indentations will be skewed (a line drawn them would
    not be perpendicular to a line drawn to the far left mark). Note that
    this is simply a paper method of recording the exact distances between
    the laser beams at 20 feet and 40 feet. The whole point is that the
    distances between the beams will be exactly the same when the sextant
    is set to the correct index error because the beams are then exactly
    parallel.
    
    By the way, if you can't find a larger indoor area, and if the Ice Age
    has arrived and pleasant weather never returns, there is another
    option. Find an optically flat mirror (or two) that's large enough to
    intercept both of the dots from the laser. You can bounce the beams
    back across your room doubling the available space. Optical flats are
    expensive, but sometimes they turn up cheap as surplus telescope
    components. The secondary mirrors of Newtonian reflecting telecopes are
    usually high-quality optically flat mirrors. Or you can just tough it
    out and enjoy this fine Siberian weather we're having.
    
    -FER
    
    
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