NavList:

Dear Red,

> > I described the story in  detail on this list about a year ago.
> Sorry, I must have missed that.

Not surprising. This was before you joined the list:-)

> Huh, so the companies are measuring the arc--
> and presumably certifying their own
> instruments based on that certification
> --without acutally measuring the *system*
> error which would include the teeth?

I am not sure that I understand what you wanted to say here.
In a modern sextant "measuring the arc" is the same as
"measuring the teeth.
A testing device (which I've seen in Freiberg factory)
sends to rays in a sextant under known angle.
Then this angle is measured with the sextant
and is compared with the sextant
reading.

> Have you corresponded with them to enquire?
> I would expect them to at least be
> open regarding what/how they measured and what avenues
> for error that leaves.

No, I have not. They can always say that their test is more
precise than my test. Besides that, the instrumental error can
change with time. (Russian manuals recommend certification every
2 years). My test consists in measurement of star-to-star distances.
There is always a possibility that I make some mistakes, or my sight
is not good, etc. I would be very interested in someone with experience
testing my sextant by measuring star-to-star or Lunar distances,
or Sun altitudes with artificial horizon. But this is a time consuming
work.

> > I cannot coat the eyepiece. The filter has to be detacheable.

> The tinting film adheres with a water-based adhesive,
> if you apply it dry, you
> can simply remove it again, like putting a bit of cellophane
> in the eyepiece for
> a minute.

You propose that I go around with my sextant and a bottle of
some chemical. Cover the eyepiece with the chemical to measure
my index correction, then remove the coating to measure a Sun altitude,
then cover again etc.?

> Or, for that matter
> matter, you could use a bit of black and white
> photographic film, partly exposed and developed.

How to attach the film to the eyepiece?

> to let you try sun sights you mentioned you weren't able to try yet.

The Sun sights with artificial horizon can be done by
blackening one of the artificial horizon glasses.
This is a solution which I will try when I come back
to the US (to my artificial horizon).
The glass of the art horizon can be blackened with a candle.

Sun at low altitudes over real horizon is another matter.
One really needs some sort of filter which can be attached to the sextant.
But this is not urgent for me. At the place where I live now, no horizon
is visible anyway, so I have fun with Lunars instead:-)

> I suppose a dedicated user could instead obtain
> one dark contact lens, and
> correct the *eye* instead of the instrument.<G>

I am not "dedicated" to THAT extent. I would rather try to make
an eyepiece filter, that I can attach to my telescope,
or live without it
as I do now:-)

Alex.


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