Slashdot Mirror
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."
Basu Gasu Bakuhatsu :chiyo:
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.
Things You Can't Do With a Giant Fresnel Lens! It's much shorter!
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!
"It seems when you are wearing #12 arc welding lenses, you can't see much short of the sun and whatever is in the lens' focus. (Like your hand on fire.)"
This one doesn't seem to have any pictures. It may actually survive the slashdotting for a short while.
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.
jibba jabba
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.
just remembered we have one of these - 6' diameter - someone thought it would help with solar collectors back in the 80's - gotta dig this out!
"Win treats sysadmins better than users. Mac treats users better than sysadmins. Linux treats everyone like sysadmins."
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....
I, for one, welcome our new Fresnel lens overlords!
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.'
and it's aaaaalll mine!
IANAPH but it the lens was say 300 feet by 300ft, would it still be possible to focus the light to a 1cm point? And if so, does the size of the lens increse the temperature?
"If you think nobody cares if you're alive, try missing a couple of car payments." Earl Wilson
Burning things has been done again and again and really isn't Slashdot (any news really) worthy.
Unless you find a way to pull a MacGyver with it and foil some terrorist plot or something I can't say I'm too impressed.
Ben
Work Safe Porn
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?
... I need one... My inner kid thinks, with a little magnifier i fried some ants, whit this i can fry/burn many BIGGER things... like: -fish -rats -big spyders -5.25" floppies -SCO stock... (worthless actually) wow i need one... added on my wish list.
Putting a windows cd backwards, plays evil messages, but it gets worse, putting it right, installs windows.
Its funny to see the lenses leaning against the vinyl siding of that house. Although the focal point is off, it would be funny/ironic in the cosmic karma sense if that lead to the burning down of that house!
Comment removed based on user account deletion
PLUS... i live in Britain. just how often could i use this (and how much less power would i have?). i've often been to Australia & NZ and have seen how much more powerful the sun is out there...
very geeky btw.
This is my Sig, this is my Gun. One is for Slashdot and one is for Fun.
In the colony, ants burn YOU!
hahaha.
The Kruger Dunning explains most post on
File exists, but access forbidden by user
Ant(Dude) @ Quality Foraged Links (AQFL.net) & The Ant Farm (antfarm.ma.cx / antfarm.home.dhs.org).
fp
Regular ants, maybe, but how about Them!?
Here's what I do: Bitty Browser & Andromeda
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.
The Scourge of All Ants!
Maybe it was a very bad idea for me to submit this story. [grin]
Ant(Dude) @ Quality Foraged Links (AQFL.net) & The Ant Farm (antfarm.ma.cx / antfarm.home.dhs.org).
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....
...
It's at least $0.01 per 10.....Americans...*shakes head*.....
When I was at a summer camp back in Junior High, I temporarily "liberated" a large magnifying lens meant for magnifying television sets. The damn thing required two of us to maneuver it into position, and in the intense summer sunlight we toasted salsa until it turned black, carved letters out of concrete on the sidewalk, and liquidated several nickels (they may look solid, but don't touch them - the inside can be quite runny and extremely hot.)
I now have two fresnel lenses, not quite that large, which I eventually will be using to set up a solar-powered forge. Also, I now have welding glasses and gloves, two things that would have come in handy when we were roasting coinage.
Obligatory Karma Whoring Link
Don't park drunk, accidents cause people.
Some guys at SGI did some stuff like this in the 90's and had a page on reality. They melted pennies and other cool stuff. I have been looking for a mirror of that site but it seems to be gone for good.
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.
As a kid I lived a half hour from the Barrington, NJ headquarters. They had a massive warehouse open to the public that was stocked with everything including motors, telescope parts, electronic components and even a bin of Jabba the Hut heads.
I picked up my first (and last) fresnel from the Ed Sci outlet, but quickly had it confiscated by my mother when I set the lawn on fire.
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
Oooooh. The first thing I did after reading that, is check out froogle:
t f- 8&q=fresnel+lens&btnG=Search+Froogle&scoring=p
http://froogle.google.com/froogle?ie=utf-8&oe=u
Is 7x11 inches good enough to burn anything cool?
SuPz.orG
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
Canon just came out with a new lens that uses Fresnel tech, or at least pseudo Fresnel. See the new 70-300 DO on canon EF lens site
It's no a perfectly flat fresnel, but it does do ladder step stuff to put a 300MM zoom in a failry small package.
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
(Only those with the most woefully deprived childhood would see this comment as Offtopic...)
They say the first thing to go is your penis. Well, it's either that or your brain. I forget which...
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)
Imagine a Beowulf cluster of these things!
This destruction is anything but aimless.
(Just ask Archimedes, he'll tell you.)
I noticed a big part of the problem with using this thing was that whatever the target was on tended to get destroyed first. What would make a good platform or stage for something like this. Second, suppose I wanted to melt something that burns in air. Any ideas on how to keep the air becoming oxidized? Maybe put in a little charcoal.
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!
Nice to know we're actually prepared for arthropod terrorism.
Perhaps the government will put a large one in space, and fry you on the spot if you don't pay your taxes!
OMG OMG OMG WTF OMG WTF BBQ STFU RTFM, OMFG OMG OMG OMG ROFL LMAO OMG WTF STFU ROFLMAO
Ah, yes, mindless destruction. Good for the spark I always say.
- Megatron, "Nemesis, Part II"
"I think so, Brain, but 'instant karma' always gets so lumpy." - Pinky
"Decepticons FOREVER!!!" - Ravage
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!
Yeah, the giant laser. I saw one once at a surplus place. I was tempted to get it. Giant dye laser with humonguous low L capcitors that probabl cost a fortune. Made from scratch. Probably by an IBM engineer that wanted to build his own rather than buy one. I could tell because IBM at the time had all these model makers, machinists whose job it was to make things for the engineers. The 1/4" aluminum plates weren't cut from 1/4" aluminum sheet. No, they were machined from solid aluminum stock. Totally over engineered. Sure sign of an in house IBM project.
first post?
"But a professor," I try to explain...
"You can't have one."
CaC03 + Heat => CaO + CO2
Happens around 200'C from memory.
ZombieEngineer
Lock up your ant farms boys, no six legged antennae equipped critter is safe around these guys!
I had time to read the whole page before coming back here and discovering that there were not yet any comments... /. starving for worthy stories???
The power of Christ compiles you.
A Random Blog
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!
Also, i could be worong, but telecopes with a glass lens also tends to split the light up to a degree like a prism, while the mirrors jsut reflect and concentrate it, so yo get a clearer image.
All Troll + "offtopic" mods are meta moderated as "Unfair", because you abused the system.
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.
"I found one of these at my school last year"
Heh heh, just like that car I found outside your house last summer.
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.
This approach doesn't scale well. There are cheaper ways to focus light. Try a search on 'nonimaging solar collectors' on google.
Even with a stock fresnell lens, it's possible that an array of smaller lenses would work better. It's also possible that the focal spot of this giant lens is just *too* hot for practical use, and the array of smaller lenses would be better.
It's pitifully small compared to this one, but I once managed to get a defective fresnel lens from an overhead projector. The fan failed, and heat of the bulb made a 1" distortion a little off-center. Makes it useless for imaging, but doesn't hurt it's energy concentration much.
Of course it's only 1/9 the area, but cost me $99 less. I haven't used for decades, since my brother-in-law and I were snapping ants on the sidewalk. (First thing I thought of, first time I played Ant City.) But it's still down in the basement, ready for the sun.
The living have better things to do than to continue hating the dead.
hrm, random destruction, count me in.
Shades of "Brazil"
The living have better things to do than to continue hating the dead.
Great. Now I know what 'original film' the Sci-Fi channel will try feeding me next month.
After 'Dinocroc' and 'Boa vs. Python' I'll have 'laser sharks' to enjoy.
"Sometimes, I think Trent just needs a cup of hot chocolate and a blankie." -Tori Amos on Nine Inch Nails
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.
I used to have a 18" fresnel lens, Dad gave it to me when I was about 12. Fun fun fun once you got some dark goggles.
Even with the smaller version, I was able to melt zinc pennies, although it took a little while. With the lens in a frame, I got a really nice pinpoint focus, so i'd imagine that the peak energy flux at target was comparable to (though much smaller in area) that of the big lens they have.
Needless to say, even the largest and most impressive ants in the yard vaporized in moments.
As long as you get them dark goggles to go with it, I'd recommend this as a toy for *any* pyromaniac child. Oh yes indeedy...
"We have to go forth and crush every world view that doesn't believe in tolerance and free speech." - David Brin
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.
*Player 2 gets railed by Player 1's Gigantic Mofo Fresnel Lense.*
W ields-A-Gigantic-Mofo-Fresnel-Lense-Bitch?
Frag Count: 121313
Death Count: Do-You-Think-That-Its-Possible-To-Kill-A-Man-Who-
now stand up and smell your chair...
of Archimedes burning ships with mirrors ?
It can heat toes up to a blistering 39804304834083408 degrees.
Uh, the fact that glass is transparent may make it difficult to melt using light.
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
More unique than an airbourne plasma laser and phase-conjugate mirror? Next you're going to be telling us you can drive a 10-inch spike through a board with your penis!
Somehow I can mentally picture Dr. Evil with a giant fresnel lens orbiting Earth and demanding one hundred terabillion dollars.
-
Roses are #FF0000, Violets are #0000FF, find / -name '*base*' |xargs chown -R us && mv zig greatjustice
Your'e on fire!
use them to carefully review SCO filings and license claims ;) in the hot midday sun :-D in Jamaica >8-D
if this is supposed to be a new economy, how come they still want my old fashioned money?
this guy always wanted Edmund Scientific's Giant Fresnel Lens.
I grew up about a 45 minute drive from Edmunds Scientific in NJ. I used to get my father to drive me there a couple times per year. I built a telescope, ground the 8" mirror myself, with parts and books I got at Edmunds. I remember the back room full of surplus electronics and optics for cheap, too.
Now I have a 5-year old boy. Damn I miss Edmunds.
So how is this off topic? I would consider the entire topic "off topic".
Our moderators must lean towards beavis and butthead thinking. This explains alot about their scoring!!
Karma, We don't need no stinkin' karma!
No, it's easy, providied you're not dumb enough to just put a piece of glass on the ground and shine the beam at it. Like most hot, melty things, molten glass is best heated in a crucible. Crucibles, surprisingly enough, are opaque and usually the right color to absorb heat - that is, they are blackened.
Solar furnaces like this one: http://www.imp.cnrs.fr/foursol/1000_en.shtml look like fun too :)
The setup can produce 1000kW of heat in a very small area, and temperatures of up to 4000 Celsius.
do all of those things promised in the hundreds of spam messages you get every year.
You really can have a bigger bust, even of you didn't have a bust previously...
You really can make other parts larger as well but some things you must already have one of...
you can make your investments larger - or at least make the fine print on your investment portfolio "Holy Roman Empire" sized...
You can watch your favorite movies and television shows on a giant screen for only a few dollars... you may need to add a cardboard box and a little creative energy but it will be possible...
Not to mention that you'll be able to cook your food almost instantly on bright sunny days as well as anything else you were unfortunate enough to accidentally direct the focal point of the lens at... then perhaps those parts won't be a large as they once appeared...
He's 13...we make sure he keeps it under his bed or someplace dark when its not in use.
isn't keeping it focused, Solar panels already do this, just add a tripod to hold the lens. The real trick, is disipating all that extra heat, as the more ambiant heat in the cell the worse its conversion ratio.
A long time ago, I tried this with a 12" lens and some fiber optics bought from Radio Shack (yes, they did have a fiber optic kit... 15+ yrs ago!)
There was no significant heat felt at the other end of the strand. The fiber optic was made of plastic though... That medium may not have been optimal for transfer of light/heat in the IR range.
My other idea (keep in mind, I was only 14 at the time) was to build a system of mirrors and lenses utilizing the fresnel lens to concentrate sunlight to a point, then bounce it off a mirror into another set of lenses which would project the light at a distant focus... thus resulting in a DEATH RAY.
build a kickass projector
it takes two.
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
The pictures show a penny welded onto a brick. If you hold your mouth right you can see the head of a bearded bald guy wearing sunglasses.
Consequences ensue.
Use to wood burn and start fires while camping - great fun for 12 year olds.
So you have a big one at the top, and then get progressivly smaller ones below it to increse the burnination capability?
Something I may have to try someday anyways
If you don't want to shell out the $$$ for one of these just go down to your office supply shop and pick up one of those flexible magnifiers the size of a sheet of notebook paper. They cost a couple of bucks. People who can't see very well use them to read phone books etc. They work great. Middle of winter with the sun low in the sky and a soaking wet beach log started to smoke instantly. So, for the price of one 35" lens one could buy a hundred of them. Tape them together to make a nice flexible array and presto, almost 6 square metres of power. Why fry one ant when you can cook the whole colony?
Whoa! Think of the things we could do with THIS!
"Faith: Belief without evidence in what is told by one who speaks without knowledge, of things without parallel." - A.B.
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. Yo, Yo- you're thinking of asphalt, aka TarMacadam. Concrete is made from Portland Cement and aggragate, sucka.
A 5x mirror is CONVEX. You need a CONCAVE mirror to focus.
I read the synopsis and thought it said "he melted several other people". I'm glad I went back and reread. Whew!
It's mandatory to wash your hands before returning to the land of Dairy Queen.
Portsmouth, VA owns one that came from a place called Hog Island. It stayed in our materials warehouse for 30 years until they built a pedestal in the harbor for it last year. It was walled up in a corner of the warehouse. I got to tear down the wall and since I knew it was a classic, nearly one-of-a-kind that was going to be forever displayed in a high profile place...I took my opportunity to be photographed with my butt on it. :-)
It's a perfect time for being wasted.
A perfect time to watch the stars.
- Burden Brothers, "Beautiful Night"
Just put a tall drinking glass in the microwave oven. Rest the pencil mine on top of the glass. Close door, switch on.
The pencil mine will eat its way through the glass all through to the bottom.
Note 1: Fill a small amount of water into the glass (or into a different glass), in order to absorb excess energy, or you'll nuke your nuker.
Note 2: Yes, the pencil mine does get hot enough to dent the glass platter that comes with the nuker. Stop in time before the mine actually reaches the bottom of the drinking glass.
Say no to software patents.
... or does their first target remind you of someone? (Hint: WWJBurn)
Having been a chemistry major in my earlier years of college, I can vouch for that. I've had acid and base burns both, and they feel about the same.
Also, if you catch light amount of sulfuric acid on your fingers quickly enough, you get the same slippery melting skin effect before it gets down to the nerves. I tell you, that was a scary moment of realization, but I got it before it did any serious damage.
If it's for-profit but free, you're not the customer -- you're the product (e.g., the Slashdot Beta's "audience").
Thanks for trying to suggest a productive use for this technology, but dude.... We're talking about destroyin' stuff!
Do you or your partner snore? - Visit www.snoring.com.au
As other pointed out Base hurt you as much as Acid. I had a colleague in my labor which had the unfortunate luck to try our "shower" [a special high pressure water shower to wash up somebody as quickly as possible from liquid substance. It has enough pressure to maintain an adult on the ground...]. He got a base on him 9-10 molar concentration (NaOH If I remmember correctly). By the time we moved him under the shower 5 meter away from where he was he had started screaming that it burn like hell on the few part of skin splashed... The lab was a mess afterward, with 5-6 cm of water everywhere.
C. Sagan : A demon haunted world:
http://www.amazon.com/gp/product/0345409469/
visit randi.org
I read the thread higher up about heating air and driving a turbine, but then you get electricity in the middle of the day, how about this instead:
Boil water
Steam rises
Condense it higher up
Save the water for its potential energy to generate the electricity during the evening when you want it.
In other words Light->Heat->Potential Energy Store -> Electricity later.
So when its sunny you make your potential energy and use it when you want the electricity.
So can we like point this at parts of Utah?
Xix.
"Everything is adjustable, provided you have the right tools"
See here.
Okay... I'll do the stupid things first, then you shy people follow.
[Zappa]
read more.
I hope I didn't brain my damage.
WTF is a "pencil mine" ?
"...for a while, had to work evenings because he was igniting balloons full of gas in the parking lot and taking holograms of the fireballs..."
Are you certian that they were holograms and not schrilian (sp?) photographs?
Any links to his work?
I'm very interested,
And... don't look into mirror with remaining eye...
This comment does not exist.
In seventh grade, during a physical science class, a friend of mine thought that it would be a funny joke to focus the sun onto my back using a Fresnel lens from an overhead projector. In the minute or so it took for me to notice (when the beam hit my skin), he had very efficiently burned through three layers of clothing!
Good times.
Can it self-destruct itselft? By placing something like a mirror in front of it, it could theoretically melt itself?
What are they supposed to do when they mix?
You're not thinking thermite are you?
'Cause you would be wrong.
As of this morning, his update log read:
Updated 2003.03.19
slashdotted 2004.05.21
But why is the rum gone?
wouldn't a giant lens be the ideal arson tool? Since it leaves no chemical evidence, there's nothing to really tie it to the arsonist.
Of course, the trouble is that you have to burn everything in broad daylight, when everyone can see you...
The Right Reverend K. Reid Wightman,
The bit of graphite that is inside the pencil.
You can buy them separately for use in rechargeable ("automatic") pencils.
Say no to software patents.
The likely reason that it seems like like they weren't getting everything to heat up was heat loss.
The two obvious paths, air, and sidewalk have some loss. But radiant heat loss will be quite significant. This is why despite insane amounts of energy being put onto the penny, you were losing insane amounts of energy.
Maybe the doctorate isn't in heat transfer.
aaah! there's a face in the image!.
they have burned the ants on mars? what gives?
...under lab conditions, you would post this article.
I guess you have to take the whole "what if its not sunny one day" factor into account. YOU MAKE THE CALL!!
Umm, I think it was something to do with evaluating gasification of coal as an alternative to natural gas. He was working as an industrial chemist for British Gas at the time, but last I heard he was somewhere in Africa doing missionary work. His work may be patented or "trade-secreted" for all I know...
Melted Penny
Face on Mars
Now we know how it must be a hoax, or a really big Martian penny.
You mean something like this?
BrookGPU
...ceterum censeo Carthaginem esse delendam.
If you increase the lens size and the focal point was in mid air, would you be able to _hear_ something? Even though air is quite transparent, at those energy densities wouldn't it start to get pretty hot and expand?
Get a big enough one and you might get a thunderclap if you ramp it up suddenly?
I figure a similar thing could happen with those huge lasers - get thunder like from lightning. Even more interesting is if that 747+huge laser ever shoots past a thundercloud towards a target.
The target could get zapped by a laser (ouch), and also get hit by the lightning discharges (ouch) down the laser-ionized air.
That could be a way to assassinate people and make it look like an "act of God" eh?
Where can i get one of these?
its not just visible light you can bend with these things (unlike magnifying glasses), if you make the rings the correct width you could focus any wavelength of light. E.g. microwaves :)
daclink
It looks like those plastic magnifying things you could get out of the back of magazines to "Enlarge your TV" I remember seeing one in some guys trash (I was a kid 79'ish). When I didn't think it would be good for anything I left it leaning against an old black metal water heater, same trash pile. When I got home from school the water heater was at the other end of the block, about 40 yards. Now it all makes sense.
If you have one of these (Grandstand Astro Wars) lying about, you'll find a great fresnel lens inside. I was a kid when I discovered it, so I'm not sure of the dimensions, but it was danm powerful. Even in England, it could set wood alight easily.
Offtopic, Inflammatory, Inappropriate, Illegal, or Offensive comments might be moderated up.
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
According to google's calculator, it takes 746 watts to make one horsepower. That means 1.5 kW is barely more than two horsepower. You might be comfortable driving a car with a two horsepower engine, but I certainly am not, and I doubt your state licencing agency would be, either. FWIW, the honda insight hybrid (considered by many to be an example of sacrificing power for efficiency) has a combined horspower of 73 horsepower; i.e. approximately 54 kW. That's what it takes to power a tiny, ultra-light (all aluminium) vehicle safely on US roads.
The front lens on a Sony PTV is the lenticular, it can be thrown away after seperating it from the freznel behind it.
It is clearer than any other lens used in rear projectors. They were also MUCH heavier than any other manufacturers.
I'd go on a Vegan diet but the delivery time from Vega is too long. --brownkitty
Maybe you'll be happy to know that in french, it's pronounced "Fre-Nel". The "s" does not have any function.
Dude, atleast one person would have thought you could hit a large ceramic crucible that had some carbon soot at the focal point and refine some ore with it the very least some old truck springs to melt down and cast into a mold...
Lasers and Solar energy how pathetic!
Check out PopSci they tweaked a microwave oven to turn into a VERY hot kiln....
Actually, I see a lot of people disclaiming the idea of using lenses for telescopes (too heavy, fresnels don't focus well, mirrors are cheaper and lighter) - however, this page (at Lawrence Livermore National Laboratory) describes a concept for a space telescope using a *five-meter* segmented fresnel lens as the objective, two spacecraft separated by a few km, and a smaller (movable) lens as an 'eyepiece', in effect creating a huge refracting telescope. Quote from the site: "Diffractive telescopes using Fresnel lenses fabricated on thin membranes offer several advantages over telescopes using mirrors; thin membrane lenses are lightweight, packageable and space deployable. Transmissive diffractive lenses are much less sensitive to surface deformations compared to mirrors, and the chromatic effects due to the diffractive primary can be completely compensated for." So, there's a use for 'em - cheap, large-scale space telescope objective lenses which are relatively robust compared to mirrors - no "Hubble trouble" with these. And if manufactured in segments, as LLNL is doing, it's easy to create *very* big lenses which fold up into a small space..
Quote from the site:
"Diffractive telescopes using Fresnel lenses fabricated on thin membranes offer several advantages over telescopes using mirrors; thin membrane lenses are lightweight, packageable and space deployable. Transmissive diffractive lenses are much less sensitive to surface deformations compared to mirrors, and the chromatic effects due to the diffractive primary can be completely compensated for."
So, there's a use for 'em - cheap, large-scale space telescope objective lenses which are relatively robust compared to mirrors - no "Hubble trouble" with these. And if manufactured in segments, as LLNL is doing, it's easy to create *very* big lenses which fold up into a small space.. take a look at the demo lens at the bottom of the page.. wonder how many pennies THAT thing'd melt. ;)
Enby in Waltham
As far as I know, it is illegal to destroy currency, whether paper or coin (in the U.S. that is) and I believe similar laws are standard in most developed countries.
----- Title 18 United States Code, Section 331 Whoever fraudulently alters, defaces, mutilates, impairs, diminishes, falsifies, scales, or lightens any of the coins coined at the mints of the United States, or any foreign coins which are by law made current or are in actual use or circulation as money within the United States; or Whoever fraudulently possesses, passes, utters, publishes, or sells, or attempts to pass, utter, publish, or sell, or brings into the United States, any such coin, knowing the same to be altered, defaced, mutilated, impaired, diminished, falsified, scaled, or lightened - Shall be fined under this title or imprisoned not more than five years, or both ----
http://www4.law.cornell.edu/uscode/18/331.html
http://www.usmint.gov/consumer/18USC331.cfm
Original research on this topic: here
Funkadelic! I was just reading about Augustine Jean Fresnel last night. You know his brother wrote the story that became the famous opera "Carmen"? He developed Fresnel lenses while working at a lighthouse. Died of tuberculosis. Here endeth the lesson.
But I could be burning that hole in my pocket with a fresnel lens. PLEASE PROVIDE ORDERING LINK.
-Clio
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