NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Greg Rudzinski
Date: 2012 May 1, 08:39 -0700
Alex, You stated:
"I don't see a reason to substitute a normal sextant with a bubble octant
if the real horizon is available, except that a bubble octant is usually
cheaper. But the performance of your bubble octant seems to be quite
exceptional."
Bubble octants are quite a bit cheaper but buyer beware for these old instruments have seen combat. I got mine four years ago with everything working except for the averager. Getting the averager working was no easy task. Fixing a bubble octant is probably an order of magnitude harder than fixing a traditional sextant. Keep this in mind before tearing into one. If things do go terribly wrong we have Bill Morris to back us up :)
"(But these are excellent results for a bubble octant!
I have never heard of the 0.1' accuracy obtained with a bubble octant,
even if this is an average of 30)"
Getting good results is more of a matter of having the correct index correction known and applied. The index correction on the bubble octant used for these natural horizon trials is +6' moa and was first determined by lining up the horizon (as normally done with a marine sextant) then double checked by lining up a twilight star. The Sun can't be used to check index error because there are no filter sets for the horizon prism.
Greg Rudzinski
[NavList] Re: Navy MK 5 Octant Using Natural Horizon
From: Alexandre Eremenko
Date: 1 May 2012 02:15
Greg,
Thanks for your explanation.
I did not realize that this was the bubble octant:-)
(But these are excellent results for a bubble octant!
I have never heard of the 0.1' accuracy obtained with a bubble octant,
even if this is an average of 30)
> There is no way to get results like I did with a
> bubble horizon even on my luckiest day ;-)
I thought tat there is no way to obtain the results you are talking
about with a bubble octant at all:-)
But I have never tried my bubble octant with the real
horizon.
> I was happy to get near marine sextant performance
> which means that this particular octant with horizon
> prism is good enough to substitute for a marine sextant
> aboard ship or small craft.
I don't see a reason to substitute a normal sextant with a bubble octant
if the real horizon is available, except that a bubble octant is usually
cheaper. But the performance of your bubble octant seems to be quite
exceptional.
Alex.
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