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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sextant accuracy (was : Plumb-line horizon vs. geocentric horizon)
From: Frank Reed CT
Date: 2005 Feb 20, 21:18 EST
From: Frank Reed CT
Date: 2005 Feb 20, 21:18 EST
Alex you wrote:
"I suspect that the "imaging resolution" limit
does not take into account a possible mechanism involving eye's
motion. Or some other mechanisms one can imagine."
does not take into account a possible mechanism involving eye's
motion. Or some other mechanisms one can imagine."
I don't see how that would make any real difference. The imaging resolution
is limited in an absolute way by diffraction and in a practical way by the array
of the cells on the retina.
I suspect that some of the old reports of "super human" resolution may
arise simply from a confusion over what qualfies as "imaging resolution". For
example, if I have a square 1cm lightbulb and I can see it at a distance of
206,265 cm or 2.06km (anyone could see it if it's bright enough), does that mean
that my eyes have an imaging resolution of 1 arcsecond? Clearly not, and if you
could get inside the eye and measure the spot, you would find a circular (not
square) diffraction disk with a width of about 30 arcseconds and no "imaging"
detail at all --just an unresolved blob. But this might get reported as an
observer being able to see a one arcsecond target.
-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
