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ArcticMyst Security by Avery

Burning, I am not impressed...






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Encap

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steve001 said:
... with using lasers to pop balloons, burn through tape..., it's a neat trick. If one wants to burn stuff using light's energy this is the way to do it. Use a very large Fresnel lens. With such a large lens one can make lava, vaporize or melt metal... . This is the way to burn stuff.
https://www.youtube.com/watch?v=svAPyyUJUCo
Click to expand...


You are right---is a novelty thing of science 3rd grade level demonstration type of thing that wears thin very very fast---you popped one ballon and you have popped every ballon on the planet pretty much.

1 box of kitchen matches does a lot more and better burning, generally.

The link you posted to solar powered Fresnel Lens melts through plaster and vaporizes aluminum instantly, is great
http://greenpowerscience.com/
 
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Crazlaser

Crazlaser

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Wow, that's basically real lava. And vaporizing aluminum, that''s insane.:drool::wtf: This reminds me of an experiment I saw Grant Thompson do on his youtube channel, with a large lens from a projector tv.
 
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steve001

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Crazlaser said:
Wow, that's basically real lava. And vaporizing aluminum, that''s insane.:drool::wtf: This reminds me of an experiment I saw Grant Thompson do on his youtube channel, with a large lens from a projector tv.
Click to expand...

That large lens is a fresnel lens.
 
paul1598419

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Fresnel lenses have short focal lengths for the size of the lens. They are also much lighter than an ordinary lens of the same FL. These are far from new, however.
 
diachi

diachi

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Yeah, you'd need a *big* laser to even come close. My dad used to get me the lenses out of overhead projectors when I was a kid, both the Fresnel lens and the convex lens - always loved playing with those.

Pretty sure I could melt a small chunk of Aluminium with one of my big 808nm diodes, managed to get some small pieces of steel to glow real bright (Xacto blade, screw etc).
 
Benm

Benm

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They can be quite impressive under full sun light. I have a couple of A4 sized plastic fresnell lenses, and those will certainly start a fire in somewhat sunny conditions.

Bigger and more rigid ones can melt rocks, basically heating any blackbody radiator up to the temperature of the solar sufrace (6000K or so). This is more than enough to melt even tungsten.
 
RedCowboy

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I have a stack of them from old rear projection TV's I'm saving for when the grid goes down and we need to cook outdoors.

53493d1476587880-burning-i-am-not-impressed-sany0737.jpg
 

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paul1598419

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They were often used in lighthouses as the lens to focus the beam off into the distance. I've seen a few large glass ones made before the last century.
 
Benm

Benm

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The glass ones from lighthouses are really impressive, especially the ones with huge diameters (a few meters or something like that). Those probably weigh a literal tonne and are not practical for anything else, but great pieces of optical history.

Sadly we don't use lighthouses that much any longer, they could be boosted to the next level using lasers ;)
 
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