John M. Dlugosz wrote in message <37cc8b6c@news.povray.org>...
>I've seen a description of Fresnel's invention a short time ago, how it was
>designed for lighthouses.  I agree, it's a normal lens with the "stair
>steps" taken out.
>
>I've seen the scratch thing called Fresnel as well, but I don't know if
>that's correct, or if the name is now applied to any kind of flat lens.


It's still a Fresnel lens, just even more compressed than the larger lenses.
The nice thing about Fresnel lenses is that you can make them quite flat and
the lens will still work.

Mark

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