NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Observations with pocket sextant in the Baltic CROSS POST
From: Alexandre Eremenko
Date: 2006 Jul 4, 02:06 -0500
Dear Red,
> If both F. and C&P checked it out your SNO-T, what exactly did they
> check? How?
I described the story in detail on this list about a year ago.
They both issued certificates. Freiberger used a precise device to check
the arc errors in my presence, C+P did not allow me to see the procedure.
In freiberger's certificate, the arc errors are written for every
10 degrees of the arc, and they are mostly negligeable, 4" or so,
13" in one place. C+P certificate says what their all certificates say:
"Free of error for practical purposes".
On the other hand, my repeated tests with star distances show arc non-
uniformity as large as 0.6'=36" (at the same places on the arc where
Freiberger
certificate shows 4"). The fault is apparently in the teeth on
the arc: they are not cut very uniformly.
It is not surprising at all that the Soviets,
in the last year of their existence, made a poor quality sextant.
Surprising (and disturbing) is the fact that two makers
of highest reputation certified it as good one.
Factory spec says that instrumental error cannot exceed 12".
And the original factory ceretificate, which I also have,
shows pure nonsense: it shows that the person who filled it
simply did not understand what s/he was doing.
(BTW I've seen some certificates on e-bay, written by people
who did not understand what a certificate is supposed to contain:-)
Of course, there is always a possibility that my observation
skills are so poor that my star-to-star tests are all faulty
and the certificates by Freiberger and C+P are correct.
But this seems very unlkikely.
> "tobacco" colored inserts in screw-in rings for the eyepieces.
Yes, many old sextants and binoculars have the same type of
filters.
> contact Tiffen or another photographic filter maker.
> If you can give them the
> pitch and diameter for the threads (either measured or researched
I doubt that they have filters of so small diameter.
This is the smallest telescope I've ever seen.
> suggest a trip to an auto parts store and $5 spent on a foo
> t of cheap "window
> tinting" material. I know, it won't be optical
> quality <G> but you should be
> able to put a tiny spot of it in the eyepiece
I cannot coat the eyepiece. The filter has to be detacheable.
But I agree that in any machine shop I should be able
to make the necessary ring with thread, the problem is only
in finding and attaching a proper tinted glass to it.
I agree that this problem is solvable.
As I said the sextant performs well to its specifications
anyway, and the filter is only needed in certain conditions
(very low Sun, or art horizon observations).
Alex.
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
From: Alexandre Eremenko
Date: 2006 Jul 4, 02:06 -0500
Dear Red,
> If both F. and C&P checked it out your SNO-T, what exactly did they
> check? How?
I described the story in detail on this list about a year ago.
They both issued certificates. Freiberger used a precise device to check
the arc errors in my presence, C+P did not allow me to see the procedure.
In freiberger's certificate, the arc errors are written for every
10 degrees of the arc, and they are mostly negligeable, 4" or so,
13" in one place. C+P certificate says what their all certificates say:
"Free of error for practical purposes".
On the other hand, my repeated tests with star distances show arc non-
uniformity as large as 0.6'=36" (at the same places on the arc where
Freiberger
certificate shows 4"). The fault is apparently in the teeth on
the arc: they are not cut very uniformly.
It is not surprising at all that the Soviets,
in the last year of their existence, made a poor quality sextant.
Surprising (and disturbing) is the fact that two makers
of highest reputation certified it as good one.
Factory spec says that instrumental error cannot exceed 12".
And the original factory ceretificate, which I also have,
shows pure nonsense: it shows that the person who filled it
simply did not understand what s/he was doing.
(BTW I've seen some certificates on e-bay, written by people
who did not understand what a certificate is supposed to contain:-)
Of course, there is always a possibility that my observation
skills are so poor that my star-to-star tests are all faulty
and the certificates by Freiberger and C+P are correct.
But this seems very unlkikely.
> "tobacco" colored inserts in screw-in rings for the eyepieces.
Yes, many old sextants and binoculars have the same type of
filters.
> contact Tiffen or another photographic filter maker.
> If you can give them the
> pitch and diameter for the threads (either measured or researched
I doubt that they have filters of so small diameter.
This is the smallest telescope I've ever seen.
> suggest a trip to an auto parts store and $5 spent on a foo
> t of cheap "window
> tinting" material. I know, it won't be optical
> quality <G> but you should be
> able to put a tiny spot of it in the eyepiece
I cannot coat the eyepiece. The filter has to be detacheable.
But I agree that in any machine shop I should be able
to make the necessary ring with thread, the problem is only
in finding and attaching a proper tinted glass to it.
I agree that this problem is solvable.
As I said the sextant performs well to its specifications
anyway, and the filter is only needed in certain conditions
(very low Sun, or art horizon observations).
Alex.
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
