T3D Re: Visual Acuity

[john bercovitz <bercov@xxxxxxxxxxx>]

> ....stereoacuity is in the range 2 to 6 arcsec....

> This number has to be compared to 1 min, which is more or less the visual
> acuity the receptor-spacing in the fovea would suggest. So stereovision
> can be 20 times more precise! Btw: the above numbers would correspond to
> a power of depth-resolution of about 3-7cm at a distance of 10m, and
> 6-15mm at a viewing distance of 5m (according to another source). This
> precison of the human visual system is always amazing for me!

Yes, these two sets of data seem to agree pretty well if I take the 3-7 cm
as 50 mm and the 6-15 mm as 10 mm:

arctan (65/10000) - arctan (65/10050) = .0018 degrees = 6.7"

arctan (65/5000) - arctan (65/5010) = .0015 dgrees = 5.4"

These mid-values are about 1/10th the visual acuity of 1' though I've seen 
cone spacing of 30" listed a couple of places as the peak density in the 
fovea and I have heard of vision approximately good enough to correspond 
to 30".  Not trying to nitpick - just thought it might be amusing to run 
the numbers.  I don't think I'd try to be too precise with numbers based
on the center values of numbers whose range is greater than a factor of 2!
8-)

I wonder if conventional acuity and stereoacuity are linked.  Actually,
there's a paper by Westheimer and another by Shor (sp?) that cover this
and I think the link was there but not as strong as one might think in 
the high-acuity range.

John B


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End of TECH-3D Digest 338
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