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Re: Sextant accuracy (was : Plumb-line horizon vs. geocentric horizon)
From: Frank Reed CT
Date: 2005 Feb 19, 19:26 EST
From: Frank Reed CT
Date: 2005 Feb 19, 19:26 EST
Fred you wrote:
"The basic conclusion both with Frank's searching and on that other
list
is the same: the angular resolution of the eye is finer than the
spacing of the rods & cones. Frank's resolution limits also were in
accord with those on the other list."
is the same: the angular resolution of the eye is finer than the
spacing of the rods & cones. Frank's resolution limits also were in
accord with those on the other list."
The standard imaging resolution of the eye is just what you would expect
from diffraction limits and the spacing of the cones. Vernier acuity, which goes
waay beyond normal resolution, apparently involves only certain very specific
discrimination tasks. Do these have direct relevance to sextant use? Some
should, but it depends on how specific these tasks are. For example, it is clear
that the eye can distinguish discontinuities in straight lines at very high
angular resolution. So if I were to use a distant power line (or other narrow
straight feature) to get the index correction of my sextant, I should be able to
get very accurate results. But what about the sea horizon? Can the eye detect
discontinuities in the visual horizon (which is not a line but instead a
boundary between light and dark) with the same hyperacuity?
And:
"In neither of them, was the question of how the eye achieves this
resolution addressed in much depth."
"In neither of them, was the question of how the eye achieves this
resolution addressed in much depth."
It does not appear that there is any solid theory for the origin of
hyperacuity (vernier acuity). One rough model apparently suggests that the
vision system is integrating over many cones to accomplish this trick.
-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