T3D Visual acuity = 1' of angle?

[bercov@xxxxxxxxxxx (John Bercovitz)]

In Kingslake's book, he says that the cones in the center of
the fovea are 30" apart.  This would be ~2 microns on center.
He then says a black and white bar pattern is resolved when 
each bar (either black or white) gets its own cone, so visual 
acuity is 1' of arc.  (This is for an eye without other prob-
lems, of course.)

If I read some other sources correctly, they are saying that 
the distance from the center of a black bar to the center of 
a white bar is 1' of arc.  So that would require cones twice
as large in diameter as Kingslake suggests if Kingslake's
scenario is approximately correct.

So are cones 2 microns or 5 microns on center?

I'm curious because this has a large effect on the required
resolution of a slide if there is to be no loss in stereo 
due to impaired resolution.

When I look at a resolution chart I have down in the basement
(lighting not too good) I get ~1.5' resolution counting from
black line to black line.  I think my eyes are OK.  It is an
interesting experiment to try.  Those of you with accommoda-
tion left can just see how far away you resolve a bar pattern.  
Some of us have to have a full chart of lines so we can see
what the finest lines we can see are at one of our sharp 
distances.  8-)

John B


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