At 09:31 AM 2/17/2003, Bill Marshall wrote:
>Here's a silly question.....
>
>Has anyone ever heard of those lenses causing a fire or damaging the interior
>by focusing the sun's rays onto a small area?  I've seen people use those
>fresnel lenses to burn ants or cook stuff, and wondered if my cargo area
>might spontaneously combust.  I can just imagine......

These lenses have the opposite effect; they're equivalent to concave lenses
of conventional type.  The ones you've seen used for solar furnaces and
such are equivalent to convex lenses.

The Fresnel part is the technique of collapsing the lens so you get the
same surface geometry and power without the weight of material.

david

--
David Beierl -- dbeierl@attglobal.net