I have a few fresnel lenses (maybe 6) that I removed from old rear projection TVs. I set them back in the original frame for playing with. At least one of them can melt glass. I demonstrated it at a sustainability fair one time and melted a line of glass on a compressed earth block. It needs a little cleaning, but can still melt glass. The others vary in quality.
I have several of these that I have salvaged as well. I keep thinking there has to be a use for them with regards to heat or power or something worthwhile, but so far, they are just toys for me. I'm confident I will come up with something though :)
While Paul has one that was used for melting glass and was tweaked a bit by Josiah in the last year or two, he could probably use another. I saw a Youtube video of a guy who mounted one to a frame and used drills mounted to light sensors to create a dual axis, auto-tracking system that would follow the sun and could melt stuff without constant hands-on moving.
I wonder if several of them could be mounted to such a tracking system, and rather than focus down to a single super-hot point, point them at mirrors and have them concentrate into a space that could heat water or cook something faster than a normal solar cooker.
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The focal length of these lenses are (if I remember correctly) about 3-5 feet. If they age close enough together they might shade one another a bit, and they would be a different angle to the sun. Maybe if mirrors were added to a lens they might help concentrate the sun through the lens.
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