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I made some further testing
of this SNO-T sextant, following an advise of
Frank (who tried it for several weeks).
His advise was to slacken the
pressure of
the misterious adjusting screw on the drum
(this tiny SNO-T screw was discussed several times
on the old list). As a result, the worm can be rotated now
with very light effort. The results seem to be satisfactory.
(Previously, more than a year ago,
I actually tightened this screw myself,
thinking
that I couldprevent or remove backlash this way).

Nov 21 IC from Sun -0.4, 4SD exact

Nov 22 IC from Sun -0.5, 4SD exact
Using IC=-0.5:
Deneb-Vega at 24d 3 observations, errors: 0.0, 0.2, 0.1
Altair-Deneb at 38d 4 observations, errors: 0.3, 0.0, 0.0, 0.3

Nov. 23 IC=-0.5 from Altair, 6 obs, sigma=0.2
Using IC=-0.5:
Deneb-Vega at 24d, 3 observations, errors: 0.1, 0.1, 0.0
Altair-Deneb at 38d, 4 obs 0.0, 0.2, -0.2, 0.2

Nov. 24 lunars:
Sun-Moon at 46 degrees, errors: 0.3, 0.2, 0.2, -0.1, 0.2,
Average error 0.16, sigma=0.15
Sun-Moon at 47 degrees, errors: 0.1, 0.1, 0.2, 0.3, 0.1,
Average error 0.16, sigma=0.09.

Dec. 2 IC=-0.45 from Sun 4SD exact, 5 obs, sigma=0.15
Using IC=-0.45
Dec. 2 lunars:
Moon-Altair at 99 degrees, errors: -0.1, 0.0, 0.4, -0.2, -0.1,
average error 0.0, sigma=0.23.

Alex.

On Sat, 2 Dec 2006, Bill wrote:

>
>
> Bill, you wrote:
> > "Point being, I seriously doubt the lasers you refer to meet the standards  of
> > both monochromatic and collimated light. "
>
> Frank replied:
> > They're real lasers. They produce monochromatic, coherent light --no
> > cheating on the terminology. All lasers have some beam spread, and you can
> > counteract it, up to the diffraction limit, using a telescope...
>
> Ok. I'm buying into that.  Been shopping.  Found a straight-line laser for
> $5 after rebate at Ace.  It's nice as the height in relation to the eyepiece
> doesn't matter much, and very easy to center on eye-side scope lens, but it
> does not produce the fine spike that a point source produces.
>
> Borrowed a friend's "Taiwan Tom" level laser complete with tripod and all
> the niceties, but the off/on knob is on the front so one cannot center the
> beam up with the scope.
>
> Finally, after realizing batteries for my aging Compaq pen/pointer gimme
> would be $12 and considering that a poor investment as the dot is more of an
> ellipse than a circle, I ferreted out a laser pointer/led light/pen at Wal
> Mart for the princely sum of $2.88!  It works very well, with a fine
> vertical diffraction line.
>
> Refining rigs to mount it now, 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.  Centering the spot on the glass/mirror section of the
> horizon mirror is simple trial and error and can be done satisfactorily by
> eye.
>
> Using George's suggesting on how to determine the distance between the
> horizon mirror and index mirror working points, I set up the rigs for trial
> runs. The distance was only 40 ft, but the results were right on (probably
> beginner�s luck.)
>
> Last sun IE check was 0.788' on the arc.  When matching the predetermined
> mirror distance, the sextant reading was just a hair below 0.8' on the arc.
>
> I'm looking forward to more stringent tests as greater distances.
>
> Thanks for the idea Frank.
>
> Alex
>
> You ready to grab some sextants, a pair of FRS radios and go play?
>
> Bill
>
>
> >
>


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