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Q & A: Fresnel Lens

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Most recent answer: 03/29/2009
Q:
Could you use a flat material to focus light? Wjat is required to focus light with refraction?
- Dave (age 16)
Cheshire, CT, USA
A:

Dear Dave,

I'm assuming you want to know if there are flat objects (as contrasted to a bulging convex lens) that can focus light by refraction. The answer is yes! A Fresnel lens does just that. It works like a normal lens, and some are in the form of a flat sheet. If you look at a Fresnel lens closely, you'll notice many thin concentric rings on its surface. All these individual rings focus light to the same point by refraction. (See second image below - it shows the cross section through the center of a Fresnel lens)

Fresnel lenses are used in a wide variety of applications, since they are thinner and lighter than conventional lenses. You can find them in lighthouses, overhead projectors and book-reading aids (as magnifiers) - where their light weight is very desirable.

Hope this helps!

- Mae

(Image source: ;

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(published on 03/29/2009)

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