The concept of a fresnel lens is really rather simple. Think of a typical convex -convex lens 2 feet in diameter (or larger in a lighthouse). One, it's very thick and two, it's very heavy! Now slice through that lens in concentric circles from circumference to centre, making a series of glass rings. Slice again across the diameter. Then, working from the outside in, shave the excess glass of the back of each ring until when laid flat all the rings now have the same height when laid upon a flat surfave. . The upper surface will be a series of ridges which once formed the convex curve of the lens. The unnecessary mass under the curve is removed saving enormous weight. Optically it is essentially the same lens but physically it is greatly reduced in depth and mass. They are also used in theatrical lighting for essentially the same reasons. On Saturday, August 16, 2003, at 01:26 PM, Automatic digest processor wrote: > > You prol'ly mean Fresnel Lense. Oriigially developed by a Frenchman and > applied to light houses. The were fantastic for collecting the light > from a lantern, concentrating it into a beam that could be projected > for > miles across the water. Most Fresnel lenses were made up of glass > pieces > that has a triangular cross section. The pieces were organized into > concentric circles and the angle of the glas set to collect light from > onw directtion and through the prism effect of the triangular cross > section, concentrate the light and project it as narrow beam of light. > The Fresnel mirror is doing the same thing, but just collecting > naturally reflected light which it projects for you to see as an image > it the miror. > |
Please note - During the past 17 years of operation, several gigabytes of
Vanagon mail messages have been archived. Searching the entire collection
will take up to five minutes to complete. Please be patient!
Return to the archives @ gerry.vanagon.com
The vanagon mailing list archives are copyright (c) 1994-2011, and may not be reproduced without the express written permission of the list administrators. Posting messages to this mailing list grants a license to the mailing list administrators to reproduce the message in a compilation, either printed or electronic. All compilations will be not-for-profit, with any excess proceeds going to the Vanagon mailing list.
Any profits from list compilations go exclusively towards the management and operation of the Vanagon mailing list and vanagon mailing list web site.