Thank you for the post about the Fresnel lens.
When engineering is both practical and beautiful, I almost want to cry. With joy.
Look at the Golden Gate Bridge, for example.
If you have not visited in person a lighthouse with a Fresnel lens (functioning or not), I urge you to do so. A working Fresnel lens is more beautiful than any chandelier.
In fact, the docent at one of the lighthouses I toured did call it a “chandelier.” < smile >
Story about the inventor (Augustin Fresnel), here:
https://www.smithsonianmag.com/science-nature/science-makes-a-better-lighthouse-lens-170677431/
As a child, he was a slow learner who showed little interest in language studies or in tests of memory. By the age of 8, he could barely read. Yet his boyhood friends, for whom he studiously determined how to increase the power of popguns and bows, called him “the genius.” When applied to optics, his genius proved to be real and considerable. Where others had improved existing lighthouse technology, Fresnel leapt forward by studying the behavior of light itself. His studies both advanced the understanding of the nature of light and produced the most important breakthrough in lighthouse lights in 2,000 years.
Fresnel worked out a number of formulas to calculate the way light changes direction, or refracts, while passing through glass prisms. Working with some of the most advanced glassmakers of the day, he produced a combination of prism shapes that together made up a lens. The Fresnel lighthouse lens used a large lamp at the focal plane as its light source. It also contained a central panel of magnifying glasses surrounded above and below by concentric rings of prisms and mirrors, all angled to gather light, intensify it and project it outward.
Regarding fresnel lenses, they’re used quite often these days with traffic lights to “direct” the light towards the correct lane/direction.
Also, Canon (and others now) uses the fresnel concept in Diffractive Optics lenses. Much more refined, especially in the newest generation, but very effective in allowing physically shorter lenses compared to their focal length.
For example, Canon’s 400 mm f/4 DO II lens is only 232 mm long, whereas their other non-DO 400 mm lens is 343 mm long. That’s a pretty substantial size differential.