Wasn't it Warp who wrote:
>Stephen <mcavoys_AT_aolDOT.com> wrote:
>> Is this the sort of thing?
>> http://www.reference.com/browse/wiki/Lens_(optics)
>
>  Why not give an url to the original article, which has the images etc.
>intact and not raped like in that site?
>
>http://en.wikipedia.org/wiki/Lens_(optics)
>
>  The article says "the most common type of lenses are spherical lenses".
>Then in the spherical aberration subsection it says that the spherical
>shape is not the optimal for light focusing but it doesn't say what is.
>
>  Why can't they simply give the mathematical function for the perfect
>lens surface instead of just saying: "Lenses in which closer-to-ideal,
>non-spherical surfaces are used are called aspheric lenses. These were
>formerly complex to make and often extremely expensive, although
>advances in technology have greatly reduced the cost of manufacture
>for these lenses."
>
>  What is the function for the perfect lens surface?

I initially thought that parabolic lenses would have perfect optics,
like parabolic mirrors do, but it turns out that the light rays are not
at the correct angle when they reach the second surface.

Here's one solution that produces a lens with perfect optics, but you
wouldn't want one of these in your eyeglasses:

http://members.shaw.ca/quadibloc/science/opt0503.htm

I also came across this news article
http://www.azom.com/details.asp?newsID=2064
Which bears the title: "The Perfect Lens is Possible According to
Researchers at Purdue and MIT", but the text says "Researchers have now
shown, through rigorous mathematical analysis, that a perfect lens is
not possible, said Kevin J. Webb, a professor of electrical and computer
engineering at Purdue."

-- 
Mike Williams
Gentleman of Leisure

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