> "20/20 is the visual acuity needed to discriminate two points separated by 

>
> So I guess 30 seconds (0.5 minutes) could plausibly be within the range of 
> normal human vision then.
>
> I just noticed the other night that as I passed under a sign telling me 
> the motorway exit was in 1 mile, I could already see the green traffic 
> lights beyond the exit. And those lights can't be much more than 24cm 
> across...

Hmm, I can see an object perfectly fine with an angle of 10^-9 degrees.

Being able to see something and discriminate between two points is 
different.

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