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: http://www.scitoyscatalog.com/Merchant2/graphics/00000001/fresnel_catalog.jpg;
http://ifa.hawaii.edu/~amann/401px-Fresnel_lens.svg.png)
(published on 03/29/2009)
