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.

--John

Bill DeWitt <the### [at] earthlinknet> wrote in message
news:37c60299@news.povray.org...
> I think you may be confusing a Fresnel lens with a diffraction grating.
> Fresnel is simply a compression of the relevant portions of a standard
lens.
> ...or maybe I am wrong. But I have used the Fresnel measurements to make a
> solar reflector that worked just like the parabolic dish reflector I
modeled
> it on.

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