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 2 days ago Bill and I tried index checks using
Frank's idea with laser pointers. We used a 120 feet
corridor, 3 different laser pointers 2 sextants
(Astra and SNO) and 2 telescopes (Astra's native
and SNO inverting).
The general conclusion is that one can indeed check
the IE this way, probably to 0.1' if one uses a POWERFUL scope.
All our attempts to focus the laser beam using Astra's native
scope at 120 feet failed. The inverting one was OK.

The test gave IC=-0.4 for the SNO.
Here are the results of todays Sun checks.
20 observations with filters YY: IC=-0.6 4SD=65.2(perfect) sigma=0.2
21 observations with filters RY: IC=-0.3 4SD=65.2 sigma=0.1
4 observations with a home-made telescope filter
(a precious gift from a member of this list)
IC=-0.5, 4SD=65.2 sigma is less than 0.1
Conclusion: some filter prizmaticity is present, probably of the
R-filter,
maybe both.
(This confirms my earlier observations from Lunar-Sun
distances that this R-filter's prizmaticity
correction is about +0.2)

I also did horizontal checks.
All 14 vertical checks give IC=-0.4 4SD perfect, sigma=0.1
All 14 handle up checks      IC=-0.5 4SD perfect, sigma=0.1
All 13 handle down checks IC=-0.5 4SD within limits (65.5) sigma=0.2

All my star checks usually fail: the results I get are inconsistent and
vary between
0 and -1'. I attribute this to my night vision deterioration (I am 52),
just cannot
tell precisely when two star images coincide. It is better with star
distances
because I can rotate ("rock") my sextant. But with index rocking will
not help.

Alex.


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