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Things You Can Do With A Giant Fresnel Lens
Ant writes "Here is a link where this guy always wanted Edmund Scientific's Giant Fresnel Lens. 'Melts asphalt in seconds!' the ad said. When he went to graduate school he met several other people with the same enthusiasm for aimless destruction through bizarre means, and just enough combined cash to make it happen. Thus the reign of terror began."
Right here: Cooking with Light.
A message from the system administrator: 'I've upped my priority. Now up yours.'
Mount it in front of your monitor for a really big image Write your name in the side of someone's car Wipe your harddrive permanently There has to be a way to increase solar cell output with these (not at direct focus of course mabey larger area at 25% focus)
"It's so convenient to have a system where everyone is a criminal" - A. Hitler
Maybe not very practical, but it might make a good paint remover. I have seen work crews remove paint from wood surfaces with a heat gun that looked like a big hairdryer, so I would think this type of lens would be helpful for stripping paint off metal surfaces such as water towers and so forth.
A love beyond compare...
Chalk actually burns under this thing.
Chalk burns eh? Creative chemistry, more like it. Here's another fun thing you can do: drop your "burnt" chalk in a glass half-full of water, let it bubble, and put your finger in it. Let me know how it feels.
So do aluminum cans. They smell really bad.
Aluminium doesn't smell bad when it burns. I suspect whatever soda pop chemicals remaining in the can do.
It seems that normal concrete will start emitting plumes of smoke just before it pops
As would burning tar, or any other heavy petroleum derivate.
* Mike's car.
Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame.
Try focusing the lens on the round plastic thing that smells funny, on the rear side of the car...
Seriously, this article is all about playing with a new destructive toy and not much about using the toy in question to do interesting science-related experiments.
I found one of these at my school last year. The first thing I did was take it to the parking lot to set paper on fire. The asphalt under the paper burned. I also melted pennies with it, and it can make holes in soda cans. Is there anything else anyone thinks I should burn with it? it's in my garage.
A perfect example is a laser communication system. A laser beam can be modulated and used to transmit audio. The receiver needs to collect as many photons as possible from the laser transmitter - hence the use of the fresnel lense. Signals can be bounced off clouds - I've heard of transmissions going over 60 miles!
The Amatuer Radio Laser Communications Page has a good primer that has a link to a lot of the basics. And no, you don't need a ham license - although it helps!
This sig seemed like a good idea at the time....
Hanging a Fresnel Lens in front of a white wall projects a nicely focused image of the room onto the wall. Depending on the arrangement of the room and windowage, its poosible to watch the world pass by on projected image. The optimum distance from wall to lens is approximately the focal length (or a little farther if the subject is close to the lens.
Just make sure the sun never gets to the lens or it will burn an arc across the wall.
Two wrongs don't make a right, but three lefts do.
Could you do something serious with this? Put the damn thing in a rig that follows the sun, and a small steam turbine under it, just how much juice could it provide?
I wish I knew the math to this, but damn, if it could provide even a small fraction of the power I use during the daytime... (by this, I mean 5-10%)
Anyone want to impress me with their math/physics skills?
You can get a free Fresnel lens by doing a bit of dumpster diving. If anyone has thrown out a 50" projection TV, the lens is yours!
NOTE: This HAS happened; I am NOT being sarcastic. I took the Fresnel lens out from the trash and stuck it under my bed, wondering what I could do with it. Now I know! (perhaps I should just eBay it for $100)
If this thing is capable of creating such intense heat (with, as far as I can tell, very little environmental impact such as that created when making solar panels) then perhaps it could be used as an alternative (and portable) power source?
I need to look into this. Heat energy can be converted into electric energy, even if it isn't all that efficient.
Useless opinions, worthless observations, and more!
I read a paper once that advocated the following strategy for getting to Proxima Centauri in a span of ~50 years. The plan is this:
1) Construct array of solar panels near Mercury (or whatever)
2) Beam resulting gigawatts of power to the Moon using small lasers/masers
3) Collect the power and use it to feed a very large laser
4) Point laser at a huge fresnel lens orbiting Jupiter (say)
5) Point fresnel lens at a solar sail, accelerating it to ~0.1c quite quickly
The lens allows your laser beam to stay focused at long range (like 4 light years). Of course it would take centuries to build the kit needed, but once it's running you can send lots of payloads for little cost (solar sails are 'cheap' to make). There are also solar sail strategies for interstellar return journeys!
I like solar sails, generally. Sustainable space travel!
They're building a huge pane of glass on the Australian desert. This pane of glass is supended a few feet off the ground, which is painted black. The air between the glass and the ground is heated, and since hot air rises, it travels toward a chimney at the center of this contraption. As it moves through the chimney, a large turbine generates the necessary power. This odd design works extremely well, but requires very bright, sunny locations that don't mind a glass pane a square mile wide!
This guy did it:
Cockeyed Presents: Incredible Stuff - Mirrored Parabolic Solar Cooker
if the answer isn't violence, neither is your silence / freedom of expression doesn't make it alright
this article is interesting because it reminds me of something i read in an old history book on mayan temples. apparently, some of them have rock cut so exactly and perfectly, a knife blade will not fit between the seams. i remember reading (or watching on tv once) about how some scientists/archeologists theorized that the maya used focused sunlight to cut the rock (specifically, big gold encrusted sun discs), and how preposterous others thought of the idea. i even remember that some scientists tried it out once with gold polished mirrors, and it failed utterly. now that we know a giant fresnel lens can burn ashphalt and make concrete crack and pop, i wonder if the maya came up with a similar technique based on a more primitive (or more advanced) fresnel-like lens. anybody want to carve up some rock to test the theory? it would make for some fun mad science to prove an old theory.
While it's very hard to verify this legend, one thing we know for sure is that Syracuse was conquered via land, and Archimedes ingenuity had an important part to play in defending Syracuse from the sea.
So yeah, this is stuff that matters, but hardly "news"
The Raven
I recall reading an article in a Canadian electronics magazine back in the mid 80s where the author created a satellite "dish" based on Fresnel theory. It wasn't a dish at all, but a large plywood Fresnel lens that focused the (C-band) satellite signal onto a feed horn behind the plywood (as opposed to a dish where the feed horn is located in front at the focal point). I don't remember if the plywood was painted with a metallic paint.
I think the mag was Electronics Today and the author may have been Steve Rimmer or David Stringer. Those guys used to do all kinds of crazy things, like mounting a dozen larger speakers (covered with sheet metal) to the front of a VW van and hooking them up to a frequency generator and amplifier. They used this rig to distort the bounced signal from a police radar gun tricking it into displaying a speed of their choice