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Douglas, you wrote:
"I note the practical results of horizon index error measurement here by Mr. 
Rudzinski, and of the results in the paper by Gordon; and the results posted 
by others here,  amount to around 0.4 minute of arc to one minute of arc.
The cone diameter is about 0.4 minute of arc.
'Normal' visual acuity (depending on the target type) is between 0.4 and one minute of arc.
Curious coincincidence, do you not think?"

But a coincidence nevertheless. The visual acuity of the human eye is NOT the 
limiting factor in LOP sights such as in that article.

Let's consider a simple experiment. You want to determine the resolution of a 
telescope and compare it with the normal resolution of the human eye. So you 
get out a standard eyechart. Let's make it one of those "Snellen E" charts 
where you look at a row of capital E's in various orientations. Now, wearing 
appropriate eyeglasses, let's suppose I can read the 20/20 line at a distance 
of 20 feet and maybe a little farther. So that makes my vision 20/20 or a 
little better and implies a resolution of 1.0 minuutes of arc or a little 
better. NOW, we grab a 7x telescope from a sextant case. I assume that this 
is a decent telescope with good quality optics. I step back to a distance of 
140 feet with the 7x telescope in my hand. Looking at the chart with my eyes 
(plus eyeglasses), that 20/20 line is now unreadable --the E's are no more 
than dots. But when I hold the telescope up to my eye, I can read it just at 
the limit of my resolution, exactly as I could read it when I was twenty feet 
away without a telescope. The elements of those E's are reduced in size by a 
factor of seven because I am seven times further away. But the telescope 
magnifies them by a factor of seven and my eye is presented with an image 
that is identical to what I could see at 20 feet without the telescope. The 
telescope allows me to resolve features that are approximately 0.14 minute of 
arc in angular size.

-FER


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