| Fresnel lenses are now much easier to make as
plastic replicas, pressed from a laser cut, computer designed
master. Large (30 cm diameter) concave lenses are sold as window
decorations and the equivalent convex lens is found undert the
cover glass in overhead projectors. Glass lenses of the same
size and focal lengths would be 10 cm thick. |
Fresnel (~1850)) designed a large flat convex lens to focus
the light from a light-house. The lens was made by cutting concentric
circular prisms.
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