Re: [ATM] mirror or lens?

[Michael Peck <mpeck1@ix.netcom.com>]

At 18:07 8/1/05, aplanatic@aol.com wrote:
>
>I find the physical difference between reflection and refraction 
>quite significant, having to do with the availability of conduction 
>electrons, among other things.  From a solid state physics point of 
>view the two phenomenon are quite different, and would not even be 
>covered in the same chapter...  In other words, it's a matter of view point.
>

Dave:

Just to belabor this fascinating subject a bit further, Born and Wolf 
derive the laws of reflection and refraction from Maxwell's equations 
in section 1.5 of Principles of Optics (7th edn.). A short quote 
might be instructive:

"When a plane wave falls on to a boundary between two homogeneous 
media of different optical properties, it is split into two waves: a 
transmitted wave proceeding into the second medium and a reflected 
wave propagated back into the first medium. The existence of these 
two waves can be demonstrated from the boundary conditions,..." (p. 38)

So, from the point of view of classical electrodynamics reflection 
and refraction are different aspects of the same phenomenon. 
Presumably you could derive the same laws from quantum 
electrodynamics. But I wasn't thinking about classical 
electrodynamics, let alone solid state physics or QED. I was thinking 
about current optical engineering practice. As far as I can tell, to 
a modern optical engineer a lens is an image forming instrument, and 
it doesn't matter if it's made of refractive or reflective elements, 
or a combination of both. That's how Warren Smith uses the word in 
"Modern Lens Design" for example, which according the back cover 
blurb gives "more than 280 worked-out lens designs" including 
reflecting and catadioptric telescopes.

Mike Peck



_________________

Michael Peck
email mpeck1@ix.netcom.com
Wildlife photoblog! http://wildlife-pix.com
Amateur telescope making http://home.earthlink.net/~mlpeck54/astro/astro.html 

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