Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!


Forgot your password?

Things You Can Do With A Giant Fresnel Lens 469

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."
This discussion has been archived. No new comments can be posted.

Things You Can Do With A Giant Fresnel Lens

Comments Filter:
  • by PissingInTheWind ( 573929 ) on Friday May 21, 2004 @09:18PM (#9222076)
    Right here: Cooking with Light [armory.com].
  • Ideas (Score:3, Interesting)

    by panxerox ( 575545 ) * on Friday May 21, 2004 @09:19PM (#9222080)
    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)
  • A good use (Score:3, Interesting)

    by KoriaDesevis ( 781774 ) <koriadesevis.yahoo@com> on Friday May 21, 2004 @09:19PM (#9222082) Journal

    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.

  • Mindless (Score:3, Interesting)

    by Roland Piquepaille ( 780675 ) on Friday May 21, 2004 @09:24PM (#9222109)
    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 have one of these. (Score:5, Interesting)

    by Qender ( 318699 ) on Friday May 21, 2004 @09:24PM (#9222111) Homepage Journal
    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.
  • Laser Communications (Score:5, Interesting)

    by Rob Carr ( 780861 ) on Friday May 21, 2004 @09:24PM (#9222114) Homepage Journal
    Besides destorying things, these fresnel lenses cand be used for all sorts of constructive fun.

    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 [qsl.net] 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!

  • Hanging wall art (Score:4, Interesting)

    by G4from128k ( 686170 ) on Friday May 21, 2004 @09:27PM (#9222134)
    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.
  • 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?
  • Re:Ideas (Score:3, Interesting)

    by DoraLives ( 622001 ) on Friday May 21, 2004 @09:33PM (#9222161)
    Wipe your harddrive permanently

    I daresay this may be the long sought for absolutely sure method for permanently removing data from a hard drive in such a way that nobody, not even the NSA will be able to recover it.

    Job well done, guys!

  • Re:Mindless (Score:3, Interesting)

    by Siva ( 6132 ) on Friday May 21, 2004 @09:35PM (#9222165) Homepage Journal
    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.

    aw, at least explain for those of us who lack the chemistry knowledge and the stock of burnt chalk what will happen...
  • Re:Ideas (Score:2, Interesting)

    by jd_esguerra ( 582336 ) on Friday May 21, 2004 @09:43PM (#9222220)

    I'm no expert in solar cells, but would it really be possible to increase output of a solar cell just by focusing light to s smaller spot ? If you are focusing light (energy) from a lens that is a square meter in area down to a cell with a 1-cm square area , how is that different than having a cell of 1 square meter in area ? Unless there are marked efficiency differences between a 1-m^2 sensor, and the 1-cm^2 sensor, the energy "captured" would be approximately the same, right ?

    Your energy output is going to be equal (in ideal sense, but always less-than that in reality) to the solar energy that hits your light collecting optics, be it a big-ass lens or a photovotaic cell. Its a thermodynamics issue.

  • by Sycraft-fu ( 314770 ) on Friday May 21, 2004 @09:46PM (#9222242)
    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.
  • by nelsonal ( 549144 ) on Friday May 21, 2004 @09:46PM (#9222243) Journal
    If you follow the sun perfectly you could figure on about 1 kW of light (cheesy rule of thumb) hitting your turbine. Assume 30% efficiency and you have 300W of electric power generated for an average of 12 hrs per sunny day. Three light bulbs (or 6-8 florescents) or one fully loaded computer (300 W power supply, no electric heat, iron, or oven. Oh and you'll need a capacitor bank to handle your inductive load when motors start. Go grab your power bill and see how many kW/hrs you use in a month and then figure out how many fresnel lens/turbine array's you would need to achive that power. Storage would be a mofo, although you might be able to sell it into the grid in your area.
  • The Warper (Score:2, Interesting)

    by mcguyver ( 589810 ) on Friday May 21, 2004 @09:53PM (#9222289) Homepage
    http://www.noah.org/acidwarp/warper.html [noah.org]
    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!
    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".
  • by gatzke ( 2977 ) on Friday May 21, 2004 @09:58PM (#9222314) Homepage Journal

    Can't you use fresnel along with photvoltaic to improve the power of the photovoltaics? Maybe not this size of fresnel, but smaller, cheaper ones to get a boost on your cells.

    I could be wrong...
  • by tokachu(k) ( 780007 ) on Friday May 21, 2004 @10:02PM (#9222328) Journal
    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)
  • by Cirrocco ( 466158 ) on Friday May 21, 2004 @10:05PM (#9222340) Homepage
    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.
  • by Roland Piquepaille ( 780675 ) on Friday May 21, 2004 @10:06PM (#9222343)
    Can't you use fresnel along with photvoltaic to improve the power of the photovoltaics? Maybe not this size of fresnel, but smaller, cheaper ones to get a boost on your cells.

    If you pair a photovoltaic panel to the same size fresnel lens, no because you'll just have concentrated the same amount of light on a tiny bit of the photovoltaic panel instead of having the same power spread on the entire surface. You can however increase the power to a smaller panel, because then you concentrate on this smaller surface the power gathered by the larger lens.

    There's a limit to how much you can concentrate the solar light onto the solar panel before destroying the panel though. For this to work, you'd probably have to keep the solar panel out of the lens' focal point, and if your lens is really big, cool the panel with water or something (their efficiency is higher when they're cool).
  • by eclectro ( 227083 ) on Friday May 21, 2004 @10:09PM (#9222356)
    I have given much thought to this, and in fact have done the math. Though it is a hassle to repeat here.

    I came up with a general number -- 1.5 kilowatts, this is about the amount of energy you would need to propel a small car (like a volkswagon beetle, old variety). This is about the same as a small gasoline engine could provide.

    While it looks like a lens like this might be able to provide the power, there are a number of issues that need to be addressed.

    One is continual focus of the lens. The position of the sun changes, as does the direction you drive, so you need to be able to quickly move the mirror. If the mirror has to swing around too much, you will lose energy to whatever you are powering pretty quickly.

    Another is clouds. You need to have a backup plan (coal? :) ) if you have an overcast day. This will vary from place to place though.

    Along the same lines, the sun is quite low in the horizon during the winter (at least for northern latitudes) and you will have difficulty getting meaningful energy/focusing consistently from solar energy. Also don't forget, you need to drive at night.

    Ideally, you would have a fuel cell as backup. But fuel cell technology is a _long_ way from being practical.

    As good as this lens is, I am pretty sure that it would fall short of the necessary 1.5 kw to work.

    But I continually think about a solar car, and plan on building one someday, even if I have to create the practical tech to make it work.

    As an aside, fuel cells by themselves are not that efficient as some have made them out to be - about 30% to 45% (at least the common ones I know about). The high efficiency would come from cogeneration (such as steam) that uses the waste heat from the fuel cell for power. In an arrangement like this, efficiency can be around 80%.
  • paper-mache' concave surface should do the trick.
  • by DustMagnet ( 453493 ) on Friday May 21, 2004 @10:28PM (#9222462) Journal
    Is there anything else anyone thinks I should burn with it?

    Glass softens and flows not much hotter than the zinc melts. In the article pennies melted in seconds, so glass should be easy.

    I know enough about glass to warn you it might explode while heating and cooling. It can even "explode" after it's been cool for a while depending on the annealing. Try small peices over copper.

  • by Zirtix ( 443841 ) on Friday May 21, 2004 @10:30PM (#9222468) Homepage
    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!
  • WMD? (Score:2, Interesting)

    by xeon4life ( 668430 ) <devin&devintorres,com> on Friday May 21, 2004 @10:42PM (#9222540) Homepage Journal
    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.

  • Re:Ideas (Score:5, Interesting)

    by uberdave ( 526529 ) on Friday May 21, 2004 @10:55PM (#9222608) Homepage
    From one of the articles: "Cylindrical Fresnel lenses provide a 7:1 concentration, allowing a single multijunction GaInP2/GaAs/Ge cell to collect solar energy equivalent to that gathered by seven cells."

    In other words, a fresnel lens does not help in terms of energy gathering. On a cost or mass per area, it does.
  • Re:It's being done! (Score:5, Interesting)

    by jamesshuang ( 598784 ) on Friday May 21, 2004 @11:06PM (#9222675) Homepage
    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!
  • Childhood Anecdote (Score:3, Interesting)

    by donscarletti ( 569232 ) on Friday May 21, 2004 @11:43PM (#9222884)
    Back in primary school we were given Fresnel lens of about half that size (still obscenely huge) as souvenirs by a short sighted tour guide. Needless to say they were confiscated immediately by the teachers so they would not be used during the course of the excursion. The problem is that they were redistributed on our first day back home, back in a sleepy drought riddled town in western New South Wales, Australia.

    Lucky the fire on the oval was able to be contained, otherwise I would have lost more than my Fresnel lens.

  • by cybersk4nk ( 727689 ) on Friday May 21, 2004 @11:49PM (#9222918)
    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.
  • Archimedes (Score:4, Interesting)

    by vlad_petric ( 94134 ) on Friday May 21, 2004 @11:55PM (#9222942) Homepage
    Legends say that Archimedes [ucar.edu] wreaked havoc through the Roman invasion fleet trying to conquer Syracuse with giant lenses.

    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"

  • Re:Ideas (Score:3, Interesting)

    by cmacb ( 547347 ) on Saturday May 22, 2004 @12:02AM (#9222963) Homepage Journal
    Actually the last time I opened up a hard drive I noticed the recording surface was no longer the dull iron oxide I remember from long ago, or even the shinier material they used later but something that looked more like a mirror. It would probably be a mistake to aim a large lense at one of these.
  • by Anonymous Coward on Saturday May 22, 2004 @12:42AM (#9223109)
    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.
  • Solar furnaces (Score:1, Interesting)

    by Anonymous Coward on Saturday May 22, 2004 @12:59AM (#9223167)
    Solar furnaces like this one: http://www.imp.cnrs.fr/foursol/1000_en.shtml [imp.cnrs.fr] look like fun too :)

    The setup can produce 1000kW of heat in a very small area, and temperatures of up to 4000 Celsius.
  • Re:Ideas (Score:3, Interesting)

    by dmaxwell ( 43234 ) on Saturday May 22, 2004 @01:04AM (#9223191)
    but something that looked more like a mirror. It would probably be a mistake to aim a large lense at one of these.

    No biggie. Just make some big spots on the platter with a Sharpie. Once a spot gets white hot, the shininess of surrounding material won't matter much.
  • by Anonymous Coward on Saturday May 22, 2004 @01:27AM (#9223311)
    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
  • by protohiro1 ( 590732 ) on Saturday May 22, 2004 @01:49AM (#9223388) Homepage Journal
    You could always use the and neutron bomb-boiling water. My mother used to do this to get rid of ants nests and it was a little frightening. Basically a kettle of boiling water kills all the ants instantly.
  • by p51d007 ( 656414 ) on Saturday May 22, 2004 @02:07AM (#9223458)
    Antabuse was widely perscribed via court order to keep people from drinking. Heck, even listerine would set it off and you'd get violently sick. I've worked in law enforcement for 20 years and I think they quit using it because it was considered "cruel"......well, if it kept them from drinking and getting behind the wheel of a car and killing someone, I think it was a good thing, but the ACLU always thinks otherwise ;)
  • by InfiniteWisdom ( 530090 ) on Saturday May 22, 2004 @02:30AM (#9223524) Homepage
    A 5x mirror is CONVEX. You need a CONCAVE mirror to focus.
  • by RollingThunder ( 88952 ) on Saturday May 22, 2004 @02:34AM (#9223536)
    I wonder if it would be possible to have a reflector added in to that, so that you can heat the bottom of the frying pan, for a nice even heat. I'm guessing that most mirrors would absorb too much energy themselves, though, and heat up too much.
  • Re:Ants (Score:1, Interesting)

    by Anonymous Coward on Saturday May 22, 2004 @04:03AM (#9223729)
    Deadly camel spiders? All they can do is scare you or give you a good pinch if you corner one.

    Anything that eats scorpions is welcome in my book! My younger brother (who was over in iraq the last time we were there ) used to regale us with tales of how many scorpions were to be found in the desert there, and of the soldier who didn't kick the side of the latrine hard enough before sitting down. When he dangled something below the rim, the scorpion stung it. *empathetic cringe of horror*

    My brother was part of a medical chopper unit, the sort of people called for just such an emergency. He said the swelling had to be seen to be believed - and that seeing it caused him to spend a good deal of time beating on the latrine every time he used it through the remainder of his stay in the Gulf!

    Thanks, I'll take the Camel Spiders anyday.

    *orders up one of the used 11" lenses mentioned in the posting* Thanks for the well-linked post, I've been looking for one this size for years! I've even bookmarked the places where I can get even larger ones in case I get some spare cash anytime soon.
  • Re:It's being done! (Score:3, Interesting)

    by Colin Smith ( 2679 ) on Saturday May 22, 2004 @05:05AM (#9223873)
    "solar cells still collect juice on slightly cloudy or overcast days, but this method doesn't work nearly as well."

    In fact the reverse is true. Infra red penetrates clouds better than visible light so even on cloudy days you can still generate. You simply size the field of mirrors to account for lowered sunlight.

    Solar II uses large tanks of hot salt and stores the heat for generation during the evening or very overcast days. It's a far cheaper and more efficient way of generating electricity than photovoltaic cells.
  • by Anonymous Coward on Saturday May 22, 2004 @06:17AM (#9224012)
    Some design considerations do come to mind. Would have to be shielded, so leaves don't blow into into the focus, and burn the thing down. Would imagine that the steam turbine portion of things would have safety valves, so that a particularly sunny day doesn't blow up the boiler. And as you said, a bank of caps. If the lens is $99, how much could the rest be done for?

    I think all of these issues can be solved relatively easily, actually.

    First issue is the leaves. Well, this thing is running at such a hot temperature that a few burning leaves are (a) not going to burn for very long and (b) not going to burn near as hot as the running temperature already is. So as long as they don't fall on something flammable, there is no problem. So basically, make big metal base to collect stuff that catches on fire and then falls, and then you're done. Or put the entire thing inside a big plastic dome so it's a closed system and leaves can never get there.

    Second issue is keeping the steam turbine part from overloading. This is actually quite easy. Normally, you keep the vaporization chamber at or very near the focal point of the lense to get maximum heat. But if it's too hot, all you need to do is move the lense slight further away from the vaporization chamber. The focal point will then be in mid-air above the chamber and the light will be less concentrated, thus leading to a lower temperature. This probably can be regulated pretty easily by a computer or even a simple analog circuit. It's just a feedback loop where higher temperatures move the lense further away, and lower temperatures move it closer.

    Storing energy is a little tougher. If you live on a hill and have two ponds, one 10 m higher than the other, you could pump a million liters of water (1000 cubic meters) from the lower one to the upper one. By doing so, you'd be storing m*g*h = 1000000 * 9.8 * 10 joules of energy, which equates to about 27 kilowatt hours. My electric bill says I used about 1200 kilowatt hours last month, so about 40 per day, so I figure 27 kilowatt hours is enough to get you through the night. Of course, this is assuming 100% efficiency... :-)

    But you're right that you don't have to be totally self-sufficient to get some benefit from it. You probably just need enough energy storage to get your through big but quick power drains when motors switch on, etc. Still, I'm not 100% sure why can't just solve that problem with a big flywheel, since you are already spinning a generator. That is, assuming you do it like the power company and keep the generators running in sync (i.e. in phase) with the rest of the power grid.

On a paper submitted by a physicist colleague: "This isn't right. This isn't even wrong." -- Wolfgang Pauli