T3D Re: Visual acuity = 1' of angle?

["Jim Crowell" <crowell@xxxxxxxxxxxxxxx>]

>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.
>

The first one sounds right.  The commonly-stated figure for "normal"
acuity is 60 cycles/degree, i.e. a black bar and a white bar in each
minute of arc.

-Jim C.

----------------------
Jim Crowell
Caltech Division of Biology
Mail Code 216-76
1200 E. California Blvd.
Pasadena, CA 91125
Tel: (626) 395-8337
Fax: (626) 795-2397
jim@xxxxxxxxxxxxxxx
http://vis.caltech.edu/~jim/Home.html


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End of TECH-3D Digest 331
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