NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Moon's 4SD
From: Frank Reed CT
Date: 2006 Nov 10, 18:28 EST
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From: Frank Reed CT
Date: 2006 Nov 10, 18:28 EST
Bill, you wrote:
"I have to admit, I hate eye glasses for cel nav with any amount of
light
pollution on land, as well as on the water in general unless absolutely
necessary. "
pollution on land, as well as on the water in general unless absolutely
necessary. "
Hey, I feel your pain. <g>
Seriously, I know it's a nuisance, but there is really no other choice if
you have significant astigmatism. A sextant telescope can accommodate a wide
range of changes in focus so people who are near-sighted can get excellent
results by re-focusing the scope, but astigmatism implies a different focus for
different orientations of your eye. There is no realistic way to cancel that out
except with eyeglasses (until you're ready for eye surgery).
No "realistic" way?? So how about something unrealistic: ask your
optometrist what they would charge to make you a prescription telescope for your
sextant... :-) Or, you could learn to look through your sextant sideways, or
maybe at a 30 degree angle. :-) If you know the orientation of the cylindrical
deformation of your eye, you could arrange to keep that axis parallel (or
perpendicular) to the frame. Then focus there. After all, it only matters that
the image should be in focus in the "up and down" direction through the sextant.
If it's blurred "left and right" (perpendicular to the frame), that doesn't hurt
and sometimes it even helps --so much so that some sextants come with
"astigmatizer" attachments designed to turn star images into horizontal
lines.
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
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To post to this group, send email to NavList@fer3.com
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