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    Re: Lunars on Sep 20th. (was Re: Perpendicularity check)
    From: Jan Kalivoda
    Date: 2004 Sep 26, 11:57 +0200

    Frank, is your telescope inverting? And please elaborate a bit on your 
    technique of holding the sextant while taking lunars. You take the distance 
    with both arms, then you lower the sextant and change the micrometer position 
    by guess, look using both arms through telescope, whether this was enough and 
    so on? Did I understand you rightly?
    
    Thanks, Jan Kalivoda
    
    
    
    ----- Original Message -----
    From: "Frank Reed" 
    To: 
    Sent: Sunday, September 26, 2004 5:40 AM
    Subject: Lunars on Sep 20th. (was Re: Perpendicularity check)
    I reduced your lunars, too, and I got the same large errors that you did. I
    agree with you that they don't make sense. When I shoot lunars I can
    consistently get results as above (about 0.2 minutes typical error in the distance). And
    you yourself consistently get altitudes off artificial horizons that seem to
    be equally good. I've been trying to think of what it could be about your
    sextant that could cause a problem. What power telescope do you use? I have a 7x35
    monocular on mine. A while back, I had the opportunity over a few weeks to
    try out over a dozen different sextants, all from major manufacturers and
    supposedly quality instruments. Nearly all had problems of adjustment that were
    inconsequential for standard position line navigation but deadly for lunars. By
    far the most important non-adjustable feature I found from my experiments was
    the presence of a nice telescope with good optics. It makes lunars so much
    easier. Incidentally, the sextant I'm presently using is a "Measure All Co." or
    "MAC", apparently a Tamaya knock-off and not expensive at all. It has a few
    design issues, and I had to re-do a calibration table for it (0,0,0,0,0,0,0,0 means
    "we didn't actually test this"), but with that monocular, it is excellent for
    lunars.
    
    A few more thoughts: the biggest physical difference when shooting lunars
    (like the sets above) is that you're holding the sextant sideways. Everything
    else should be exactly comparable to a Sun sight off an artificial horizon
    (except shade error in the horizon shades which you can test this week when the Moon
    is full). Is the index arm of your sextant tight against the frame. If it
    shifts a little when held horizontally, that might yield an error. And how do you
    feel about fatigue when you're holding the sextant horizontally? Do you sit
    when you shoot these? I have a little hand tremor, and I find it helps a great
    deal to sit and brace my hands when shooting lunars. Also, as I've mentioned
    before, I grab the frame of the sextant with both hands instead of keeping one
    hand on the micrometer. I find that the Moon moves slowly enough that I can do
    fine adjustments by lowering the sextant to a comfortable posture, nudging
    the micrometer, and then holding it up with both hands again to check. I would
    be curious to know if any of this helps.
    
    Frank R
    [ ] Mystic, Connecticut
    [X] Chicago, Illinois
    
    
    
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