NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: "Table top" index error measurement
From: Frank Reed CT
Date: 2006 Jul 12, 17:14 -0500
"BTW, I checked several level like this on the e-bay
and one advertisement says that "it creates a dot-spot of light
at 300 ft distance". You were talking of 500ft.
Are there levels of different quality?"
That advertised distance probably refers to the accuracy of the level of the
laser beam relative to the level's base. Some for example will claim "1 inch
in 300 feet" though I expect that these claims are somewhat exaggerated. For
the IC measurement test, the level range makes no difference. The actual
range of visibility of the laser dot is much greater than 500 feet especially
when you aim it through he sextant's telescope and focus it.
"Can you invent a good arc uniformity test using a laser beam?"
I have given it a fair amount of thought, as you might expect, and I don't
think there's any trick that would work, apart from building traditional
collimating projectors. For "home use" I consider Moon-Jupiter lunars using a
sextant mounted on some sort of tripod to be the best test of arc error.
And you wrote:
"I tried your other test, for the drum excentricity,
with lines of computer screen, but with no conclusive results: the testing
range in my appartment is too short, and I was lazy to make an arrangement
with fixing sextant and computer outdoors."
I believe your results simply indicated that your sextant does not have any
micrometer drum eccentricity. When we discussed this before, I recall you had
enough space for any significant error to become apparent. You measured a
zero because there was no error.
By the way, the sextant in which I found significant micrometer drum error
many moons ago is now my most reliable sextant. I tried the oldest trick in
the "home fix it" book: I took it apart, and put it back together, changing
nothing obvious. More often than not, this solves the problem, and it did in
this case. I think the parts of the micrometer were literally off-center. Now it
works great.
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
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From: Frank Reed CT
Date: 2006 Jul 12, 17:14 -0500
"BTW, I checked several level like this on the e-bay
and one advertisement says that "it creates a dot-spot of light
at 300 ft distance". You were talking of 500ft.
Are there levels of different quality?"
That advertised distance probably refers to the accuracy of the level of the
laser beam relative to the level's base. Some for example will claim "1 inch
in 300 feet" though I expect that these claims are somewhat exaggerated. For
the IC measurement test, the level range makes no difference. The actual
range of visibility of the laser dot is much greater than 500 feet especially
when you aim it through he sextant's telescope and focus it.
"Can you invent a good arc uniformity test using a laser beam?"
I have given it a fair amount of thought, as you might expect, and I don't
think there's any trick that would work, apart from building traditional
collimating projectors. For "home use" I consider Moon-Jupiter lunars using a
sextant mounted on some sort of tripod to be the best test of arc error.
And you wrote:
"I tried your other test, for the drum excentricity,
with lines of computer screen, but with no conclusive results: the testing
range in my appartment is too short, and I was lazy to make an arrangement
with fixing sextant and computer outdoors."
I believe your results simply indicated that your sextant does not have any
micrometer drum eccentricity. When we discussed this before, I recall you had
enough space for any significant error to become apparent. You measured a
zero because there was no error.
By the way, the sextant in which I found significant micrometer drum error
many moons ago is now my most reliable sextant. I tried the oldest trick in
the "home fix it" book: I took it apart, and put it back together, changing
nothing obvious. More often than not, this solves the problem, and it did in
this case. I think the parts of the micrometer were literally off-center. Now it
works great.
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
