[ATM] Re: Fresnel lenses and correcting spherical abberation bycomputer.

[mdholm@telerama.com]

>I) Fresnel lenses are inadequate for any but the most crude applications, but, 
>as a matter of fact, in these days of nanotechnology and laser machine tools,
>would it be possible to produce a fresnel lens as a spiral with millions of
>grooves, somewhat like an old-style record, but with optical quality. This
>would be as a flat lens. There would still be color aberration. 

A Fresnel lens is also flat, or, at least much more nearly so than an ordinary
lens.  If you made a Fresnel lens with the required small feature size, you
would produce a very nice optical flat.


>In these days of computerized corrections, what of a CCD which takes the image
>from a perfect spherical F1 or F2 mirror and corrects for aberration?  Thus,
>the hard part could perhaps be circumvented. Would this be possible? 

Precisely what the Hubble space telescope crew had to do after it was launched
with optics having a lot of uncorrected spherical abberation.  You notice that
they were sufficiently unhappy with the results to spend huge amounts of your
tax dollars to fix it using "conventional" optics.

Mark Holm
mdholm@telerama.com
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