Re: the smallest reflection?

From: tadchem (thomas.davidson_at_dla.mil)
Date: 01/07/05 

Date: 7 Jan 2005 10:35:55 -0800

mikephilbin1966@yahoo.co.uk wrote:
> "The OP's question was badly posed."
>
> I wanted to find out if neighbouring atoms reflect each other in
their
> surfaces... or if not that, how small can a 'mirror' be to produce an
> image on its surface? I wonder if there's an image of the smallest
> reflected object? What was wrong with that?

If this is *really* your question, then I must agree that the original
question did miss the mark.

What you are asking is "how small can a mirror be (and still) produce
an image?"

Reflection is described here:
http://scienceworld.wolfram.com/physics/Reflection.html

Only 'specular reflection' can produce an image. Objects smaller than
one wavelength of light (about 700 nm) scatter the light rather than
reflect it in a way that preserves information about the angle of
incidence.

> Your further discussion about the properties of the human eye and the
> limits of telescope resolution is a little off-topic IMHO.

Is it really? Does one pixel produce an image in your estimation? Or
two? Or four? How many pixels *does* it take to produce an 'image'?
Old dot-matrix printers and displays used to produce monochrome letters
using a rectangular array of 35 pixels. A capital "A" would look like:

..*..
.*.*.
*...*
*...*
*****
*...*
*...*

Of course, the more pixels you have the better the overall image
quality.

The 'pixel' in an analog image would be defined as the smallest unit of
a visual image which could be discerned as distinct from the
neighboring elements, and is therefore dependent upon the physiology of
the eye.

Given this fact, the eye determines what constitutes an 'image.' For
example, if the eye has, say 1 arcminute resolution, then the smallest
'image' would be 5x7 arcminutes. The size of the mirror needed to
produce this image would then depend on how far away from the observer
the mirror is - double the distance and you will need 4 times the area.
At 0.5 meter (about arm's distance) that would be about 0.7 x 1.0 mm.

Your eye may be able to 'image' newsprint at arm's length, but it
certainly cannot image the same newsprint across a large room. Size
matters. Distance matters.

At 100 meters, you would need a mirror that is 15 cm x 20 cm for the
same quality image - one that will reflect a crude representation os a
letter of the alphabet.

Tom Davidson
Richmond, VA

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