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    Re: Vernier sextant
    From: Alexandre Eremenko
    Date: 2007 Mar 10, 21:27 -0800

    I just re-read my message and found an error:
    of course 0.2=12", not 6" as I wrote several times.
    Below is corrected message:
    On Mar 11, 12:16 am, "alex"  wrote:
    > > I like seeing the raw numbers!
    > > Fred
    > Here are some preliminary tests of the old vernier
    > C. Plath. After collimation adjustment.
    > March 10. IC from Sun, average of 3:
    > IC=-50", 4SD=64'42" True value 64'.4=64'24"
    > March 11, IC from star (Rigel) -1'10".
    > GMT 2 a.m. Star distances (corrected for IC=-1'10")
    > Betelgeuse-Rigel: 18d35'50", error 14"
    > Betelgeuse-Sirius:27d05'30", error -6"
    > Betelgeuse-Sirius:27d05'30", error -6"
    > Betelgeuse-Sirius:27d05'40", error +4"
    > Aldebaran-Sirius: 46d01'50", error -2"
    > Aldebaran-Sirius: 46d01'55", error +3"
    > Aldebaran-Sirius: 46d01'50", error -2"
    > The scope used was 12x, inverting.
    > Here are the results with SNO-T, 6x inverting scope:
    > March 11, IC from star (Rigel) -0.5
    > GMT 3 a.m. Star distances corrected for IC=-0.5'
    > Betelgeuse-Rigel: 18d35'.5, error +0.2=12"
    > Betelgeuse-Rigel: 18d34'.8, error -0.5=-30"
    > Betelgeuse-Rigel: 18d35'.4, error +0.1=6"
    > Betelgeuse-Sirius:27d05'.6, error -0.1=-6"
    > Betelgeuse-Sirius:27d05'.8, error  0.2=12"
    > Betelgeuse-Sirius:27d05'.6, error -0.2=-12"
    > Aldebaran-Sirius: 46d01'.2, error +0.5=30"
    > Aldebaran-Sirius: 46d01'.6, error +0.4=24"
    > Aldebaran-Sirius: 46d01'.6, error +0.4=24"
    > So, as I expected, a vernier sextant seems more
    > accurate, but of course it is MUCH harder to use.
    > The mirrors (and filters!) are very small. It is hard to catch
    > the star, unless you preset the distance. The telescopes
    > have very tiny field of view, it is hard to keep the two
    > stars in the field. The picture is good only at the center
    > of the field, and only if your eye is at the center of the eyepiece.
    > I suppose that on a small boat I could use no telescopes, only the
    > zero-tube. Only the 12x inverting scope can be used for IC with
    > Sun. For all other scopes the shades are too small and let the
    > Sun shine straight to your eye.
    > In SNO inverting scope you see the sky like in a wide screen cinema:-)
    > No need to preset the distance, you can just scan the sky.
    > The scale of the C. Plath is very hard to read, especially at night.
    > With SNO, reading a scale to 0.1' takes few seconds,
    > even without light, while on the
    > vernier sextant, more than a minute. You have to look VERY carefully
    > to read the scale to 10" (approx 0.2'). And it takes time.
    > Roughly speaking, a series of 5 observations of the same distance
    > takes 3 minutes with SNO and 10-15 minutes with the vernier C. Plath,
    > mainly because of the slow reading of the vernier scale.
    > Finally SNO is light, while the old sextant is heavy, and my hand
    > shakes,
    > especially with a 12 x scope.
    > Shortly speaking, it is a very different experience with these two
    > different types of sextant.
    > Alex.
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