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John,

With the Davis Mark 3, I was using an artificial horizon, mostly a
mirror, to shoot stars and planets.  I got so I was consistently
within about 8 miles.  I determined, mostly with the Davis, but
confirmed with the Husun, that inaccurate leveling of the mirror was
the main culprit for the errors, by comparison to water or oil.  I
was shooting at night from my deck and going inside between shots, so
thermal effects were minimal: the index error of the Davis was fairly
stable, and I got pretty good at checking and zeroing it out.  The
lack of a telescope on the Davis Mark 3 is a disadvantage, as is the
half mirror, half plain view, so that you never see overlapping
images coming smoothly together.  A micrometer is also a necessity
for precise movement of the index.

Recently, I have been using a blackened pie pan with vegetable oil,
which is less noxious than motor oil.  You don't want the oil so thin
that surface tension distorts the surface, but it needn't be too
thick, and needn't be colored dark.

I expect the errors in my early shots were due to poor technique.

Happy New Year!

Fred

--------------------------------------------------------------------------
Frederick V. Hebard, PhD                      Email: mailto:Fred@acf.org
Staff Pathologist, Meadowview Research Farms  Web: http://www.acf.org
American Chestnut Foundation                  Phone: (276) 944-4631
14005 Glenbrook Ave.                          Fax: (276) 944-0934
Meadowview, VA 24361

   

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