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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."
Lets hope this doesn't get into the wrong hands! This can be worse than WMD's!
[intekra] - [www.plex.nu]
And to think, when I was a kid I had to settle for burning ants with a magnifying glass.
Right here: Cooking with Light.
A message from the system administrator: 'I've upped my priority. Now up yours.'
Now the ants really don't stand a chance!!!
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...
I wonder what his Terrorist Quotient is?.
Hmmm.
A friend and I were discussing what to do with all of our AOL CD's. We both came up with the idea that you could make a similar device out of them.
Welcome! You've got fire!
bash: rtfm: command not found
Sharks with...giant Frensel Lenses attached to their heads!
Meet Brood X of the 17-year Periodical Cicada.
Snap! crackle! pop!
Why waste such a monster on mere ants. I realize there are some of you out who would think of a certain movie and popcorn (lots of popcorn), but you've got to agree this is more unique.
This is just like the magnifying glass and ant game only this scales up to poodle sizes. Oh well. If I ever have a son...
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.
Now the Dept. of Homeland Security is going to order various municipalities to block the sun.
What?
you'll love this flash game: Ant City
A message from the system administrator: 'I've upped my priority. Now up yours.'
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?
Or what if you had a few massive ones in space, could you focus enough energy for use in a fusion reactor? You'd amplify all of that free energy and I don't really know what I'm talking about. Perhaps you could attach it to a shark's head.
Playing with a toy is the POINT of a toy. I have a new Radeon 9800 Pro that, I am made to understand, has a pretty bitching vector unit that can be used for scientific calulations, rendering and the like. It is not used for any of these educational pursuits, however, and is instead used to render lightsabers which I then use to cut up bad guys it also renders. In other words, I bought it as a toy.
It doesn't sound to me like they ever intended to do much science, it sounds like they intended to fuck around and burn shit, which they did with a high degree of success.
Not as big, maybe 14 inches across, but overhead transparency projectors have a big square fresnel lens in the base. Since a lot of businesses, schools etc have moved to LCD projectors, you might be able to find an old overhead that no one cares about. Still concentrates a lot of light; you can't look at the spot and it'll burn lots of things. Probably not metal, though.
Cooking idea: Take a length of thin all-thread and turn it with a slow motor, with a matching nut fastened to a board so that the all-thread and motor are slowly pulled along. Spear a few hot dogs on the all-thread and set the lens to a medium concentration. Spin up the motor, and the sun will cook the hot dogs in a spiral....
...
I used to quite enjoy absing ants with a little 5x7 fresnel lens (as well as fireworks, water, a shovel, and, well anything else pretty much). I saw these giant ones in ES and figured they would be the ultimate ant-abuse. You could probably create a fairly wide circle in which the temperature would be sufficient to roast an ant. So rather than zapping them one by one, blanket a colony and watch the burnination.
It's pronounced fer-NEL and it's spelled Fresnel because it's named after the french guy who invented it.
of a Nuclear Bomb.
Imagine kicking over an ant hill, then frying thousands of the little fuckers with each sweep of the beam when they come pouring out. Considering you can melt nickels and cut soda cans in half with this thing, it's possible you can actually [i]glass[/i] that anthill!
Just make sure it's fire ants. Those bastards deserve it...
Almighty Railgun
You Speak a Lethal Gospel!
Bloody Gibs Follow.
Do not taunt giant Fresnel lens.
I don't want knowledge. I want certainty. - Law, David Bowie
Probably not, and yes. A lens of that size would be extremely difficult to build and operate. Instead, you'd use an array of smaller lenses, or even better, mirrors. If you look at large telescopes, most use mirrors in part because of weight issues and manufacturing issues with lenses over say 1-meter.
The size of the lens does increase temperature, or at least the energy density at the focal point. A bigger lens (or mirror) can capture and direct more solar energy.
http://www.noah.org/acidwarp/warper.html
/sarcasm
A frenzel lense + acidwarp = good times in a college dorm room. A 10 foot wide light show on your wall is pretty cool. People seemed to like it but covering your computer with a lense and a cardboard box was a little nerdy.
Or...you cal sell these on eBay!
175" DIRECT BIGSCREEN BIG SCREEN HOME THEATER TV KIT
Sell kits to create 175" large TVs on eBay! The 175" 6.5x Lens Home Theater Kit is amazing! Simply put, it is a Projection unit that when attached to your ordinary TV will project the image up to sizes of 175".
A buddy who was in the army was busted for showing up drunk, and they made him take antabuse. According to him, when you're taking it drinking even the smallest amount of alcohol makes you puke puke puke.
John
Aluminium doesn't smell bad when it burns. I suspect whatever soda pop chemicals remaining in the can do.
And very possibly the paint they use to put the logo etc... on the can. He also stated that the aluminium can smelled really bad, not the aluminium that the can was made of. So when referencing to the can in that way would mean everything involved that makes it an aluminium can.
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.
While the expierments they did were fun, then did put some science into it.
The FAQ
Impressive as destroying a penny may seem, I estimated that we may have only managed to get maybe 10 percent of the available energy hitting the lens (roughly 1kW) into the penny:
* Mass of a zinc penny: 0.0025 kg
* Specific heat of zinc: 390 J/kgK
* Melting point of zinc: 419.58 degC
o Thus 20degC to about 420degC takes 390 J
* Latent heat of fusion for zinc: 1.1x10e5 J/kg
o Thus to melt the penny takes about 275 J
* We heated the liquid zinc considerably as well, but I will ignore that.
o Total energy in the penny: > 665 J
* It takes something under or around 6 seconds to melt a penny:
o 665 J / 6 sec gives us a lower limit of about >= 111 Watts
* Sunlight at the earth: 1365 W/m^2
* Transmission of the earth's atmosphere: maybe 65-70% at this angle with some clouds?
* Area of the lens is about 1.1m^2
o Power on the lens: approx. 1000 W
o Power to the penny >= 10.0%
It made a great project, the most sophisticated object I had built up to that point. It blew as a science experiment, since I didn't have a plan of action other than to melt things, nor a thermometer that could measure it's limits. In retrospect a turkey probe might have worked. I did succeed in liquifying a number of types of solder.
I only rated a participation ribbon at the fair, but one of the science teachers took it off of my hands for $75, recouping my (dad's) material expenses and then some.
Luke, help me take this mask off
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!
Projection tv's use them! :)
since I repair them for a living, ive actually done this.
its quite fun, but do be careful!
I like using the fresnel from a 60" projection tv the most
I have burned up phone books in no time with it, and I have tried cans, I got one to melt.
next time you see a projection tv in the trash, get the lens.
the lens will be the innermost of the 2 (or 3, if there is a protective screen)
have fun!
"But a professor," I try to explain...
"You can't have one."
I can't believe, with all the talk of putting one in space, nobody has used the words "DEATH" and "STAR" just yet.
Glad I'm the first. I think.
Useless opinions, worthless observations, and more!
there goes my plastic army men collection
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!
You can also build your own giant spiral fresnel reflector at home.
The Quotation at the bottom of /. after I read this article was:
"Is something VIOLENT going to happen to a GARBAGE CAN?"
I think there is more to that fortune program than is generaly acknowledged.
--HC
So I'm jump'n up and down screaming show me the money.
Behind the Strategic Defence Initiative missile shield. A giant magnifying glass in space, to burn incoming missiles, or enemy cities.
My rights don't need management.
As would burning tar, or any other heavy petroleum derivate.
Concrete doesn't contain the slightest amount of petroleum. You're thinking of -asphalt-, which is entirely different.
What smoked was contaminants on the surface of the concrete, and possibly some stabilizers. It popped because of the moisture in the concrete expanded- concrete doesn't handle much except external compression very well.
Aluminium doesn't smell bad when it burns. I suspect whatever soda pop chemicals remaining in the can do.
No, more likely the label ink.
Please help metamoderate.
that's actually how some solar power stations work. They have a bunch of mirrors that aim the sunlight to a glass globe filled with water, the water boils out and powers a turbine, condenses out and returns to the globe via a valve and pump.
Overall it works better than solar cells because it's so simple and you harness the heat energy rather than the light itself, but therer's only economy to it on a large scale, you need enough space to get a huge amount of water to constantly boil. Also, it's significantly harder to get this thing working on less-than-ideal days; solar cells still collect juice on slightly cloudy or overcast days, but this method doesn't work nearly as well.
Still, a good way to apply solar energy when in conditions that permit. I'd like to set up a small unit with a fresnel lens and 'boiling globe' to generate hot water (which I'll pump through a radiator) for my house in the winter. The problem I see is with safety, that beam has to be EXACTLY where I want it or I'll burn the house down.
"Sometimes, I think Trent just needs a cup of hot chocolate and a blankie." -Tori Amos on Nine Inch Nails
It sounds cartoonish, but what if someone discovered how to concentrate the suns rays to a specific point on the earth using a similar, but bigger lens.
All that would be needed is a big enough lens and a geostationary satellite, it wont even need to be manned.
Just a thought.
-Xeon
Real programmers can write assembly code in any language. -- Larry Wall
I melted asphalt with good 'ol gasoline.
One thing that cannot be overstated is the use of eye protection. And, whatever is selected for that application must handle IR as well as visible light. (Nearly all of the UV is absorbed by the plastic the lens is made out of, so it is not much of a factor.)
Using such a lens, to focus solar radiation, can produce power densities equivalent of a Class-IV laser; where the warnings typically read "avoid exposure to direct or scattered radiation". Even if focused to a spot size of 4cm^2--at an estimated 1kW--the power density would still fit 2.5W/mm^2. This is the same level as a 10W laser, with 2mm beam focus.
Granted that the focus is only at one point, it is easy to overlook when scattered radiation--from a "point" source--can be dangerous.
As the article states, use very heavy welding goggles, and maybe have some sunglasses on under those! It is also recommended to ensure that the goggles cover the infrared parts of the spectrum effectively.
Also note: laser safety goggles would be ineffective for this application, due to the fact that they typically use dichros, which typically are not very "wide-band". They reflect very specific wavelengths--very efficiently. But, since solar radiation is very wide-band, a lot of it will still get through.
...the original uber-cool use of the Fresnel lens, namely, in the first actually useful lighthouses.
Find the biggest "beauty mirror" you can. These things have a regular mirror on one side and a 5X mirror on the other. Use the 5X side to focus a beam of destruction wherever you wish.
Lucky the fire on the oval was able to be contained, otherwise I would have lost more than my Fresnel lens.
When Argumentum ad Hominem falls short, try Argumentum ad Matrem
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
Your'e on fire!
Try American Science and Surplus (sciplus.com), much more amusing catalog, and way cheaper than Edmunds.
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
A 5x mirror is CONVEX. You need a CONCAVE mirror to focus.
This lens, or the current replacement model (35" radius) at $225, seems cheaper than a m^2 solar cell. How about mounting the lens over a small cell? Where can I find the efficiency curves for solar cells, graphed across the total incident light wattage? If the curve peaks above the ~400W:m^2 incident on my roof at noon, I can mount the cell to intersect the cone of focused light, along the way to the focal point. Judging from the experimental results at the "Fresnel Destruction" site, the focal point itself probably offers "nonlinear" power transfer (exploding cell). But somewhere in between might be a cheaper solar collection array. OTOH, if cells' max transfer efficiency is at below 400W:m^2, maybe it's time to consider this concentrator on a glass/water->steam/turbine. In which case, where are the efficiency curves for that apparatus?
--
make install -not war