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License:   Attribution Non-commercial Share Alike (by-nc-sa) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Intro:   Giant Fresnel Lens Deathray: An Experiment in Optics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

step 1:   Acquire The Lens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

step 2:   Build a Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

step 3:   Eye Protection!!! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

step 4:   Measure the Focal Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

step 5:   Acquire Focusing Lens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

step 6:   Lens Scaffold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

step 7:   Support Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

step 8:   Lens Mount . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

step 9:   Installing the Lens Mount . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

step 10:   Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

step 11:   OK - Let's Burn Something! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

step 12:   Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

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Intro:  Giant Fresnel Lens Deathray: An Experiment in OpticsSo you don't have access to your own rail gun or military space laser....but never fear, we'll use the 1000 Watts/m2 of free sunlight in your backyard! But how?

....A 13 square foot magnifying glass!Seriously. A solid glass lens that size would be silly, but instead we can use a 4 foot wide Fresnel lens. You know, those clear, flat things with the ridges, you find themon overhead projectors and rear windows on some buses? The idea is pretty simple: a Fresnel lens is just a normal curved lens chopped into thousands of little rings, butjust as effective.

The ProjectThis instructable (my second) chronicles my progress over the last month or so on this Fresnel deathray. Each step was figured out in real time, but the general idea isthis: once you have your giant Fresnel lens, all that remains is to build a frame to keep it straight, and hold perpendicular to the sun. While you can stop here and enjoythe blinding energy of the nickel-sized spot you get at the focus, I went further and attempted to collimate the light into a straight beam. I ordered a focusing lens onlineand constructed a scaffold to hold it in place, but ultimately found the Fresnel lens to have imperfections standing in the way of proper functionality.

Disclaimer: This device is extremely dangerous, and will INSTANTLY set things on fire! It's extremely cool, but I'm not responsible for anything that happens if youdecide to ignite yourself, your house, the forest, or anything else. Also, if you decide to skip the eye protection step, I hope you like braille.

Image Notes1. Project logo.

Image Notes1. Giant Fresnel Lens Deathray!!!

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Image Notes1. Hot stuff!!!

step 1: Acquire The LensFor many future scientists, the destructive power of magnifying glasses provide hours of fun in the backyard (although I do not believe in burning living creatures,whatever the size). But everybody already has a magnifying glass. Where are we gonna get a 60-inch Fresnel lens?

They can be had online, but only for substantial piles of cash (from $80-$150 on Ebay ), which is why few people ever enjoy these devices. Traditionally, the actual lensis by far the biggest cost in a project like this, with lumber and hardware being almost nothing if you already have the tools. And now, I will impart to you the ultimatesource of FREE giant Fresnel lenses:

...Rear Projection TVs.Every rear projection TV uses a Fresnel lens the exact size of the screen to focus the image. The screen has several layers:

Outer cover (optional) - Some TVs have a clear layer on the very outside....keep it, it could be useful in another project.Lenticular lens - This is the hideous outer screen with 1000s of vertical lines. The purpose of the lines is to spread each pixel outward so you can see the screenfrom the side. It will probably rip apart as you separate the layers.Fresnel lens - this is the innermost layer - clear with millions of circular ridges on one side. The crown jewel of the TV.

Two excellent sources of free rear-projection TVs:

1. Craigslist! Go to the free section on your local Craigslist community, and you'll probably find dozens of massive, usually broken projection TVs being given away. SayBilly has a TV from about 10 years ago, and when it breaks, Billy decide to upgrade to a newer technology. Big-screen TVs usually weigh 200-400 pounds, so all Billywants is someone to make it disappear. If you have a truck and at least one strong friend, this is a great option especially if you don't like option 2.

2. The Dump . If your local dump recycles TVs, you may be fortunate enough to find a pile of TVs sitting around there. My dump doesn't allow scavenging, so we justmade sure there was no one around, and helped ourselves to the front parts of TVs and scored 3 giant lenses.

Once you have your TV screen, peel the layers apart (you may need to cut some tape along the top) and extract the precious Fresnel. Admire your plunder, anddispose/recycle the TV carcass.

Image Notes1. It's a goldmine! Pick the biggest and most convenient TVs, plan a pickup time

Image Notes1. This is how big the Fresnel lens is....

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and collect!

step 2: Build a FrameThe first thing you'll notice about your lens is that it flops around and refuses to stay straight. The lens absolutely must be flat in order to work right, so we need to build aframe. This will also prevent it from being bent or cracked.

Note: the ridges on one side of the lens are extremely delicate and scratch effortlessly. A few scratches won't affect performance, but look terrible. Try not to drag thelens against anything.

Materials Required:

At least 15 feet of lumber - I recommend 1x2" boardsPlywood or misc. scrap wood20-40 wood screwsPower drillTape measure & pencil

Holding the LensThe goal here is to secure the lens in a frame. The most elegant way to do this is to cut a groove down the length of each piece of wood, so the lens fits into the slot. Bylowering the saw blade on my table saw so it only stuck up about half an inch, I was able to cut perfect grooves down the boards.

Cutting the FrameOnce you have your grooved beams, you'll need to cut them just long enough to come together with the lens nested into the grooves. Make sure the grooves are all onthe inside, and after measuring exactly how long each side should be, cut the sides at 45° angles so the corners look nice. I used a miter to get the precise angles here.

AssemblyOnce the frame pieces are positioned around the lens you can pull everything together. We sandwiched each corner between two pieces of plywood and put screwsthrough all 3 layers, but there are lots of options for this part.

It's a little complicated, and the method varies depending on what tools you have available.If you don't have a table saw, there are other ways to make a groove, or youcould trap the lens with multiple boards. If you have any kind of workshop you should be able to rig up something. I don't advise screwing directly into the lens though,because it might crack.

Once your frame is done, you can move the lens around safely. Now BEFORE you go out and start burning stuff, I must urge you to wear the strongest sun glasses youcan find, glacier goggles are better, but nothing short of welding goggles are really going to protect your eyes.

The light spots these lenses can produce are literally as bright as the sun.

On that note, be extremely careful where you put this lens. If it's sunny out, the thing shouldn't even be left outside...you never know when it might decide to focus and setyour house on fire! Once again I am not liable for anything, including forest fires, so use your head.

Image Notes1. Mitering tool2. Saw blade - muhahahaha!

Image Notes1. Ends of the side beams, complete with lens grooves.

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Image Notes1. Lay it all flat and make sure everything fits before getting out the drill.

Image Notes1. Anything along these lines will work for holding the frame together, includingmetal brackets (we didn't have any at the time).

Image Notes1. The complete framed lens

step 3: Eye Protection!!!This is such a good idea, I decided to make it a whole step. Let me tell you - throughout this project you will spend a lot of time playing with this device, and you'll want tolook at the focus a lot to see the results.

However, you will find that after a few seconds, spots linger in your vision when you look away. The center of your retina will become more and more desensitized until itstarts taking permanent damage. Then you won't be able to see anything.

When you're looking at this spot, it may not seem so bright. That is because your eyes are already being desensitized. Thus, you have to wear at very least some darksunglasses. With welding goggles, you can't really see anything except the focal point, so I recommend glacier glasses (used in mountain climbing so you aren't blindedby the sun reflecting off of ice).

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Image Notes1. Young Frankenstein knows best.

Image Notes1. Glacier Glasses

step 4: Measure the Focal LengthRather than proceed with building the rest of the device, at this point you need to measure your lens' focal length. This is the distance from the lens to the spot of light itwill produce. This distance will only be correct when the light rays hitting the lens are parallel to each other, and perpendicular to the lens. In other words, the light has toeither be sunlight or two parallel laser beams, and hit the lens dead on. Unless you live at the equator, with the sun straight up, measuring the focal length is actually quitedifficult. After a lot of frustration I decided to use lasers.

Materials Required:

2 (or more) laser pointersA levelSome flat groundA T-squareA tape measureA large, rigid screen

We want to find the point in space where parallel light beams bending through the lens intersect. This is the focal point, and it will be straight out from the center of thelens.

Laser SetupTo set up our parallel beams of light, put your two laser pointers on either side of a book or something so that they're parallel. The goal is for the lasers to beperpendicular to the lens, so make sure they're on a level surface. Turn them on and aim the whole setup straight at the lens.

Meanwhile, have someone hold the lens straight up, using a T-square to make the lens perfectly vertical. You'll get two weird diffraction patterns on the wall behind thelens.

Finding the FocusNow, with your tape measure extending out from the base of the lens, hold your screen up so the two lasers hit it. Move it back and forth until the two spots converge.When they do, see how far from the lens your screen is.

This may sound confusing, but the pictures should help. I recommend trying several times, maybe moving the lasers around, so you can see whether your results areconsistent. For my lens, the focal length was about 40 inches (about 100cm) which is average for especially large Fresnels.

Image Notes

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1. 2 laser spots

Image Notes1. Tape measure - make sure it's parallel with the lasers.

Image Notes1. You can see very strong diffraction effects here because the ridges on the lensare as small as the wavelength of visible light.

Image Notes1. Too close2. Ah, perfect alignment!3. Too far

step 5: Acquire Focusing LensNow that you know the focal length of your Fresnel, it's time to get a diverging lens to bend the light into a beam. This will go right at the focal point, so you get as small abeam as possible.

Benefits of Creating a Beam:

Objects don't have to be right at the focal point to burst into flames!The beam can be further manipulated - magnified, reflected, put through a prism, whatever floats your optical boat.Ridiculously intense light beams are like lasers - they're awesome .

Optics RefresherIn optics, the strength of a lens is measured by its focal length (stronger lenses have shorter ones). To cancel the converging effect of the Fresnel lens, we need to eitherdiverge the light before it gets to the focal point (use a diverging lens with a negative focal length) or converge it after the light spreads out beyond the focal point (usinga converging lenses like a magnifying glass).

Diagram 1When two lenses are far apart, it's useful to think of light in terms of geometry and angles: the focusing lens has to be strong enough that its focal length is small so thatthe light spreading out from the Fresnel's focal point is completely captured by the second lens.

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From basic geometry, we know that the second lens has to have at a ratio ratio of diameter to focal length at least as big as the Fresnel lens in order to capture all thelight. This means if the second lens has a focal length fB , it has to have a diameter of at least

dB = fB (dA / fA )

where dA and fA are the diameter and focal length of your Fresnel (use the larger width since the Fresnel is not a circle).

Diagram 2With a strong enough lens (the one I got had a focal length of 35mm), you put the lens 35mm (or whatever) past the Fresnel's focal length. The light will then be bentinward, forming a beam. Of course, this will only be approximate, so you'll have to move the lens back and forth until you find the correct distance.

Optics AppletAn excellent resource for basic optics is this Optics Applet I've found. You can't really use it to get real-world numbers, but it's very handy for planning and understandinghow lenses interact. Place a "beam" on the x-axis, then a couple lenses (you can adjust the focal lengths by dragging the little white squares).

You can find lenses in lots of random places online, and the closer the focal length is to your measurement, the better. Also, bigger lenses are preferable because giantFresnels typically don't create a very small focus spot (between 1 and 2 inches wide) so you'll need at least a 2" wide lens to capture all the light.

Where I bought my lens:Surplus ShedThere are other places I'm sure, especially educational sites and the like...but it may be hard to find the exact lens you need. I should also mention that you want a glasslens, plastic simply won't do for this intensity of light.

Image Notes1. This is the main focusing lens I ended up ordering - 57mm diameter, 40mmfocal length. It's really fat. Note that one side is much more curved than the other(this is important later).2. Yay, Christmas tree!

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step 6: Lens ScaffoldNow that we have a set of focusing lenses, we need to devise a scaffold to hold them in place out in front of the Fresnel lens. After a good deal of thought we concludethe easiest way is to use thin (1x1) wooden stakes held together by plywood gussets.

Materials Required:

4 1x1 stakesScrap plywoodWoodscrewsDrill, countersink if available2x4 plank2" hole saw (or larger)Several right-angle brackets

Basic StructureOdds are you're going to do this your own way if you try it, so I won't go into too much detail about the construction. I assembled the sides first (minus the 2x4s) by cuttingthe 1x1 stakes with a miter saw to get the necessary angles, then cut plywood gussets to hold these together. We used 2 right-angle brackets (inside corners) to attachthese gussets to the plywood crosspiece that will eventually hold the lenses.

Note: A very important thing here is the orientation of the Fresnel lens. I found out the hard way that when the flat side of the lens is facing the sun, it doesn't work right(but well enough that you might not notice). So make sure the ridges are facing out, away from the scaffold - that means they'll be facing down if you build this with thelens on the ground, as I did.

After the sides are completed, two long plywood gussets secure them onto the side of the frame. Since we want the whole device to rotate about its center of gravity(somewhere between the Fresnel and the small lenses), we need a strong beam that passes through that point (hence the 2x4 s in the diagram), so we screwed the 2x4sonto the necessary gussets, providing a substantial increase in strength.

Finding the Center of GravityTo find the center of gravity of this whole scaffold (it will be along the centerline of the 2x4), you and a friend each grab one of the 2x4s and see where the thing balances.You'll want to choose a point closer to the Fresnel (so the Fresnel wants to hang down) because the lens assembly hasn't been installed yet. Finally, drill 1/4" or 5/8"holes (depending on the carriage bolt in the next step) through the points you choose.

Note: when using wood screws in the small wooden stakes, you definitely want to pre-drill/countersink holes, because wood this thin is very easy to crack.

Image Notes1. Lens scaffold (without 2x4s)

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Image Notes1. Nice mitered 30 degree cuts

Image Notes1. All the pieces ready, leaning against my ride2. Neighbor's house......muhahaha!

Image Notes1. Screws holding the support beams to the gusset, and the gusset to the lensframe

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step 7: Support BaseThis lens scaffold we now have needs to rotate around so it can aim up at the sun. To accomplish this we came up with a super simple, super sturdy base made from 5blocks of wood.

Materials Required:

One 8 foot 2x4Around 8 feet of 2x6 board8 medium lag bolts2 big lag bolts2 carriage bolts and nuts6 washers2 wood spacers (use the lightening holes you cut out for the scaffold)

The DesignYou can see the basic design from the diagram. The planks are held together with large lag bolts - to use these, drill clearance holes through the first part (as wide as thepart of the bolt without threads) and a pilot hole through the second part (not as wide, so the threads can bite into the wood). Then you screw the bolts in with a ratchet.It's very tight, and very strong. A few of these should hold each part together.

You'll want to measure the lens scaffold first , then slightly overestimate the width for the base so you can get it between the two supports easily (the spacers will takeup the rest of the width).

Mount the Lens ScaffoldWe want to put a couple holes at the top of each support, and insert a suitable collection of a spacer, washers, a nut and carriage bolt (see the diagram).

Once the pivot is together, you can use a wrench to tighten the bolts and lock the scaffold in position.

Image Notes1. Real men use BOLTS! HU-AH!!!

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Image Notes1. It's always nice to knock the edges off your boards with a file.

Image Notes1. The completed base and scaffold.

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step 8: Lens MountClearly, our death ray is missing something. If you swivel the lens up so it's perpendicular to the sun's rays, you'll just get a spot of bright light on the piece of plywood atthe focus. Once you do this (yes, I recommend it - but don't let the thing catch on fire), you'll know just where to put the focusing lens.

Materials Required:

2" PVC expansion jointYour favorite epoxyMiter saw or hack sawSand paper (60, 150)

Lens TubeThe easiest way to set up the optics here is to mount the main focusing lens on the end of a tube around 2 inches wide. This will do exactly what this instructable does -collimate the light into a smaller beam. In a sense, the entire device is already doing this with the sun's parallel rays, but we want the smallest beam possible.

Up until now, I was troubled and lost as to what I would use for this part. What was needed was essentially two tubes inside each other, the inner one allowed totelescope in and out easily, but be able to stay put. Then, while wandering the aisles of Home Depot I found the perfect part: a PVC expansion joint for 2" conduit pipe. It consists of two pipes, the inner one having two o-rings and a lot of silicon lube , allowing it to slide in and out of the outer pipe beautifully. It also happened to be aperfect fit for my 57mm focusing lens.

Preparing the TubeThis was fairly straight forward - the inner tube had a rim sticking out past the ridge where the lens wanted to sit, so I made quick work of it with a miter saw (a hack sawwould work equally well, just take it slow and rotate the tube as you're cutting). After a quick sand, the tube was ready for the lens.

EpoxyI rifled through the adhesives toolbox, found something appropriate for both glass and plastic (Duco Cement) and glued down the lens. A day later someone knocked thetube over and the lens popped off, so I decided to use epoxy to seal the lens in. This worked better (the specific epoxy isn't that important, just pile it up around the sidesof the lens to keep it in).

Note: Since diverging light is entering this lens, we want the least curved side of the lens (assuming your lens isn't symmetrical) facing out so the angle of incidence islower, minimizing loss of light by reflection. Imagine a stone skipping off a pond versus a stone dropping straight down (which is what we want in this case).

Image Notes1. Perfect fit!

Image Notes1. Goodbye, rim.

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Image Notes1. Sanded with 60 then 150 grit (make sure to remove any plastic grains frominside the tube).

Image Notes1. The less curved side of the lens is facing out.

step 9: Installing the Lens MountOne morning I woke up and found the sun actually out. The past week had been mostly overcast , with almost no sunlight hitting the deck where this project sat. So I ranout, put on my glacier glasses and pulled the tarp off the device.

AimingA simple way to aim at the sun is to rotate the device until its shadows are parallel to the supports on the ground (if the ground is flat). This means the sun is directlyforward. Then all you have to do is rotate it so the lens is closer to the sun, and an intense spot of light should form on the lens scaffold.

Even in the middle of winter at this latitude, a 1-inch charred spot formed in a few seconds. It wasn't exactly in the center of the plywood beam, meaning the device wasn'tfacing perfectly towards the sun.

Lens MountI didn't expect the light spot on the plywood to be so small. This meant that the focus was right on the plywood - farther than I expected. And since the lens assembly canonly extend forward (towards the Fresnel), I had to recess the tube past the plywood. We accomplished this with a primitive housing made of 2x4 beams and plywoodsides.

The 2x4s were ripped to a width slightly less than that of the lens tube, so the plywood sides squeezed the tube in place. If you decide to mount the lens this way, becareful not to accidentally crack the tube. But even better, think of a better way to attach it, and make the lens scaffold stick out at least 4 inches past the focal point.

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Image Notes1. Sunlight, at last!

Image Notes1. Shadows parallel to supports.

Image Notes1. INFINITE.....POWER!!!!

Image Notes1. The view through my eye protection - not as intense, but you still get visionspots if you look for too long.

Image Notes1. X marks the spot (sort of).

Image Notes1. The inner part of the tube is free to extend in and out, and the outer tube istrapped by the slightly bent plywood.

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Image Notes1. Bolting on the last part of my death ray!

Image Notes1. The epoxy we ended up using to secure Mr. Lens.

step 10: TestingDespite it being December 22nd, winter solstice, the shortest day of the year, I proceeded to test out the completed lens system. But even with the least possible sunlightto work with (several hours before noon, at 37o latitude, we got a very satisfactory spot of blinding energy at the focus. When the device was aimed so that this spot fellon the secondary lens....nothing happened.

Failure AnalysisDespite moving the lens tube back and forth through the focal point, no beam of light formed beyond the lens mount. To find out why the light wasn't cooperating, wedecided to do a beam visualization by blowing dust to reflect the light. We first used flour, but then switched to water mist (from a sprayer) since it's not as messy.

The light funnels into a highly concentrated point, as expected, but then basically fizzes out. If your Fresnel deathray is doing this, most likely the Fresnel lens isbackwards and flat side is facing the sun, rather than the ridged side. Getting this right is essential to getting a good beam profile (which we'll see in the next step).

Since the secondary lens is convex, i.e. it bends light inward, the incoming light has to be diverging in order to form a straight beam. Since the light from the Fresnelseems to disperse randomly past the focal point, almost no light even entered the secondary lens. Other Fresnel lens devices on the internet demonstrate good beamshapes, such as in this picture .

Image Notes1. Intense light converging on the focal point, just like it should.2. But where does it go?

Image Notes1. While this concentration of light (visualized by spraying water) looks neat, itseemingly doesn't enter the lens.

http://www.instructables.com/id/Giant-Fresnel-Lens-Deathray-An-Experiment-in-Opti/

step 11: OK - Let's Burn Something!Update: at the suggestion of foobaz utne, I flipped the Fresnel lens around so the ridges are facing the sun, and found a dramatic increase in lensperformance. The secondary lens still isn't working right, but I was able to upgrade from melting zinc pennies to liquefying solid copper ones and destroyingnickels!

First TestInspired by similar Fresnel experiments floating around the net, I decided to try melting a penny. On winter solstice, I found that a zinc penny melts within a minute whenheld in the focus. Solid copper pennies (from 1982 or earlier) wouldn't melt, but probably would during summer. Copper's melting point is almost 2000oF compared toZinc's 790oF. See the first row of images for these tests.

Round 2With the Fresnel lens oriented correctly, I had another crack at melting those coins. The following video and the second row of images shows my results.MUHAHAHAHA!!!

Note: Copper's melting point is about 2000oF, but Nickel's is 2600o. So it's highly possible that only the copper in the coin (75% copper, 25% nickel) melted, resulting inthe mutilated pitted surface.

Image Notes1. Penny held in the Fresnel's focus.

Image Notes1. The copper plating didn't melt, it just crumpled between the tweezers.2. Zinc slag that poured out .

http://www.instructables.com/id/Giant-Fresnel-Lens-Deathray-An-Experiment-in-Opti/

Image Notes1. Wetting down the deck is almost as good an idea as not melting zinc over yourdeck!

Image Notes1. It's also handy to have a thing of water to cool off molten coins in.

Image Notes1. A solid copper penny didn't melt, but turned yellow (I'm no chemist, but I don'tthink this is oxidation since it's not green/blue...).

Image Notes1. It's hard to see, but after reversing the Fresnel lens the beam profilebecame much nicer.

Image Notes1. Hot stuff!!! Image Notes

1. This is what happens to pennies who drink and drive.

http://www.instructables.com/id/Giant-Fresnel-Lens-Deathray-An-Experiment-in-Opti/

Image Notes1. Can you even tell what this used to be?

Image Notes1. Solid copper penny shredded by the deathray (temperature at least 2000degrees F!)

step 12: ConclusionConclusionClearly, a giant Fresnel lens with an area of ~1.2m2 is a powerful asset. Assuming the maximum available solar energy hitting the ground is around 1000W/m2, this lenscould theoretically concentrate 1200W of power into a square centimeter. Of course, at this latitude and time of year, around half of the maximum sunlight is available sothis would make an excellent summer project. But even during winter, the fact that I could easily melt solid copper and make a nickel red hot is pretty damn cool.

Additional InformationThere are a good number of websites about the joys of giant Fresnels, namely:

"Now We're Cooking with Light""Random Destructive Acts via Focused Solar Radiation""How to Melt a Penny"Howstuffworks ArticleWikipedia Article

Other usesPerhaps the most valuable thing you can get out of this instructable is the source for these giant lenses. There are loads of of them heading for landfills, or recycling, orgod knows what else, so reclaim these things and put them to use!

Note: You may think, as I did, "Gee, I bet I could make a super efficient solar panel with one of these". But according to this discussion board that isn't a very goodidea, and could ruin your expensive solar panel. You could certainly power a small heat engine like this stirling engine though, by trapping all the light in a black containerthermally connected to the boiler. A company working on this technology, but using reflectors instead of lenses, is Stirling Energy Systems .

Thanks to everyone for your comments and suggestions.Special thanks to foobaz utne for solving my problem with the Fresnel lens focusing properly.

I hope you enjoyed this project, and I will either update this if I further develop it, or post other solar-related projects in the future.

Image Notes1. Solid copper penny shredded by the deathray (temperature at least 2000 degrees F!)

http://www.instructables.com/id/Giant-Fresnel-Lens-Deathray-An-Experiment-in-Opti/

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 Mike McGill says:  Nov 26, 2010. 4:57 PM  REPLYHi, This is very impressive. I reckon it would make an extremely clean method of melting metal for casting, using a cast iron crucible at the focal point. Iremember reading years ago about an experiment in Switzerland, where a hillside was covered with parabolic mirrors controlled and focussed by computer.They burnt a hole through a six inch steel plate in less than a minute.

 John S says:  Jan 2, 2008. 7:03 AM  REPLYIt may not work on a solar panel but it it should enhance the efficiency of the passive solar heater I have been thinking of building to help heat my house. Bybuilding a metal frame with soda pop cans stacked inside and a clear front and mounting a lens like this in front of the glass front I should multiply theamount of heat collected from the air flowing past the stack of solar heated aluminum cans. I just realized it would only be in focus a small part of the daysince the solar heater box will be mounted on the south wall of my house. Still it shouldn't hurt anything. I might have to make the back of the box out ofheaver metal.

 Helioskannon says:  Mar 28, 2008. 1:49 AM  REPLYBe careful with that, Aluminum melts at 1200 F... (Copper at 2000, and it _destroyed_ the penny) It could well work if it's not in perfect focus, just becareful and don't burn a hole in your house. Though, a well designed solar furnace to melt metal would be awesome. If I can find one of those lensesanywhere, I'll see what I can do, and if it works, post an instructable.

 Silence says:  Nov 26, 2010. 1:50 PM  REPLYThats some intense heat.You could purpose that heat for electricity in 1 of 2 ways.Stirling engine, Steam turbine !!

 Shiftlock says:  Nov 26, 2010. 4:51 PM  REPLYBoth of these ideas have been done. There's a Youtube user called GREENPOWERSCIENCE that has posted videos of these in action. Heplays with all kinds of solar. In his most recent video, he cuts a beer bottle in half by lightly scoring it, then using a small parabolic mirror to stressthe glass. It's neat.

 badideasrus says:  Aug 29, 2010. 12:27 PM  REPLYi found a source of the lenses. craigslist. search for rear projection tvs. most are free for the haulin, and over 55 inches. start the burnin!

 BtheBike says:  Nov 26, 2010. 8:07 AM  REPLYYes . I got 2 from curbside garbage also. Right now with black friday ,these things are all over the place like old CRT's . Maybe there should be amandate to collect these lenses for 'green' industrial use ,or ship to 3rd world countries for use.

I wonder if the lens from old seeing glasses could also be used for the focal lens in a pinch .

http://www.instructables.com/id/Giant-Fresnel-Lens-Deathray-An-Experiment-in-Opti/

 badideasrus says:  Jun 16, 2010. 12:57 PM  REPLYthat was a similar idea that i had. use fresnel lens to heat metal ffor forging and smelting. no need for coal or wood. just stick the metal bar under thelight for a few seconds and then continue forging. i've heard of parabolic mirrors being turned out of alluminum (lathed.) why? it would be simpler tojust take molten metal and pour it on on a spinnin disk. the liquid metal would take a parabolic shape, and you would not need an insanely large latheto make it. i'm seeing 12 foot mirrors made with an old car motor.

 dslkjdflkjsdlkjds says:  Dec 20, 2008. 4:27 PM  REPLY--NOTE!!:1) Not all big boxy televisions are rear-projection! Smaller and especially older ones may simply be CRT (not rear-projection) which means there is noscreen, just a metal cathode inside a solid glass tube. On the inside of the front face of the tube is a very thin and very toxic shiny phosphor coating. There isno lens, other than--perhaps--the glass itself. I repeat: what you are looking at--the outermost layer of the display--in a CRT television is the solid glass tubeitself.2) UNDER NO CIRCUMSTANCES BREAK ANY GLASS IN THE TUBEIf you have to break glass or ceramic sealant, you're doing it wrong.The toxic phosphors will flake off and start floating around like dust, it *will* get everywhere.Yttrium (in the red pixels), for one, causes lung disease.

Some tubes have a band of metal glued to the tube which looks like it is holding a screen to the tube. They are not. While it is possible to remove it, you willfind nothing more behind it than a solid glass seam which is part of the main tube, not a seam holding the tube to a screen.

 Silence says:  Nov 26, 2010. 1:55 PM  REPLYIdentify rear projection TVs quick by a flat, gray or black screen surface (the Lenticular lens as described above) with lines. You'll know it when you seeit.All CRTs that I've seen have glass screens.

 BOOM5601 says:  Oct 19, 2010. 11:29 AM  REPLYWho cares? if you get a crt by mistake, you've just gotten yourself a flyback!

 xirekaj says:  Oct 6, 2009. 10:38 AM  REPLYBasically, if you can't tell the difference between a CRT and a rear projection tv then this and almost every other project on this site is not for you.

 jerbear1978 says:  Nov 26, 2010. 1:19 PM  REPLYSo, if I read through your instructable correctly, I read that you never got your smaller lense to work correctly? Could this be fixed by re aligning your lenseholding structure?

 Jon B3 says:  Nov 26, 2010. 12:36 PM  REPLYNice. I've been experimenting with solid-state electricity generation using Peltier modules. This very well may be the ideal super hot energy required.

Cooling ideas for the other side of the module are welcome but a CPU/GPU cooling kit seems like it might do the job with a remote radiator/fan.

 bahi says:  Nov 26, 2010. 11:38 AM  REPLYThe light path visualized using spray water, a photograph worthy of a photography prize.One of the best instructables.Congrats.

 boy says:  Nov 26, 2010. 7:30 AM  REPLYcupertino california that might be steve jobs old tv

 sitearm says:  Nov 26, 2010. 7:08 AM  REPLY"Muah hah hah" indeed... awesome! : )

 meritsetgo says:  Nov 22, 2010. 7:33 PM  REPLYany old slide projector could be your source for the secondary lens needed for this project, the older it is, usually the better the quality of the glass

 voltskaterzb says:  Aug 2, 2009. 1:09 PM  REPLYThat what you did was illegal

 LetsExplodeSomething says:  Sep 7, 2010. 6:05 PM  REPLYhow so?

http://www.instructables.com/id/Giant-Fresnel-Lens-Deathray-An-Experiment-in-Opti/

 nutsandbolts_64 says:  Oct 11, 2010. 3:03 AM  REPLYprobably something about not mutilating or modifying coins (haha, mutilating...) for all i know there's a law in the US about not changing, in any way,a coin. I dunno who stuck the law there.

 Darwinfish says:  Oct 13, 2010. 11:52 PM  REPLYYou can damage/deface/spindle/mutilate coins without any legal issues, so long as you don't pass off the coins for more than face value. So ifwhatever quarters are made of now was suddenly in high demand, and the quarter was thus worth more than $0.25 in scrap, melting them downand selling them would be illegal.

Paper money is an issue. Coins aren't.

 nutsandbolts_64 says:  Oct 14, 2010. 2:53 AM  REPLYOh... I just pulled my above comment from a memory of a comment of the same subject.

 badideasrus says:  Jun 16, 2010. 1:00 PM  REPLYANGST! i reply to myself about a problem with my reply, and it moves my seco;nd reply to the top! i'm havin a bad day.

 badideasrus says:  Jun 16, 2010. 12:59 PM  REPLYdang it. i put a space between the topic of lenses and the topic of mirrors and instructibles goes and deletes it. how do i maintain clarity here? >(

 Leejin says:  Jan 27, 2010. 1:48 PM  REPLYHell, use it to coil water then use the steam to turn a turbine on your home. If 4 square feet of the suns power can do this... then why the heck has no oneapplied this to creating energy on a massive scale. I've heard of the mirrors heating up that huuuge column and boiling water, but this seems like anIMENSE form of energy. Ugh, the gubmn't annoys me.

 michael_p_fogarty says:  Jun 9, 2010. 5:00 AM  REPLYLOL if it aint fossil fuel then they dont get rich (Down with all earth killing capitalists). look up sterling hot air and sterling steem engines just emagin whatyou could do adding a fresnel lens to those woot woot.

 DrSimons says:  Jan 27, 2010. 7:42 PM  REPLYWell yeah...I've done some research into what people are already doing with this. 1 design doesn't use water, it just uses an air-based Sterling engine,which is heated by mirrors. Parabolic mirrors are infinitely more logical than fresnel lenses, because they're easier to make and can be much bigger, andwon't fade in the sun.

In Spain (and other places now, I imagine) there is a 20MW solar power concentrator. Unfortunately I think there is a theoretical maximum temperatureyou can reach solely by concentrating sunlight (which I believe is the surface temp. of the sun) but you can still get an insane amount of power. The bestthing is all our power plants are already based on heating water in some way or another, so the turbine/generator part has already been perfectedthrough a century of engineering.

I have absolutely no clue why people aren't covering the entire surface of Arizona, New Mexico, Nevada, etc with mirrors.

 nutsandbolts_64 says:  Apr 11, 2010. 8:03 PM  REPLYFor one thing it's the cost. The second is they can't find a way around the most obvious problem: The sun goes up, and it goes down. And I guess Iconsider myself lucky being in the equator:D

 DrSimons says:  Apr 11, 2010. 10:34 PM  REPLYWell compared to PV cells, mirrors are pretty dang cheap....for solar thermal, they don't need to be very fancy. Also, tracking the sun is extremelyeasy because with parabolic troughs, you only need to move them in one dimension. The movement of an entire field of collectors could bemanaged by a $10 circuit board. However, it's probably sill cheaper to burn coal, and cost is the only thing that anyone seems to care about...

 perfectfire says:  Aug 6, 2010. 4:50 PM  REPLYSo you don't even have to adjust for the time of the year (regarding the tracking in one dimension)?

 nutsandbolts_64 says:  Apr 12, 2010. 8:53 PM  REPLY Well, looks like I stand corrected at the "cost" part, but they do have to do something about loosing sunlight when they needed it most. Yes, Ihave heard of using liquid salt to keep the water boiling through the night, but there should be a more commercially viable solution. Nevermind car batteries for large scale power production that's for sure. 

 Leejin says:  Jan 27, 2010. 1:48 PM  REPLYboil water * not coil water...

Haha

http://www.instructables.com/id/Giant-Fresnel-Lens-Deathray-An-Experiment-in-Opti/

 michael_p_fogarty says:  Jun 9, 2010. 5:04 AM  REPLYBoil in copper coils woot woot free power and distled water!!!!!!

 specopps117 says:  May 8, 2010. 9:26 PM  REPLYHow many lumens up close, would be as bright as the sun at its distance from the Earth?

 Deadalus says:  Feb 15, 2010. 9:57 AM  REPLYWere you ever able to work out the problem with the secondary lens ?  It ,may be that some form of lasing element would work.  The guts of small laserpointers which are almost free may be worth trying.

 Ev says:  Jan 10, 2010. 11:02 AM  REPLYHere's how I found the focal point...  Get a trigger pump type of fluid sprayer, either a glass cleaner sprayer or you can buy empty plant misting devices at ahardware store. Put the lens in the sun and spray water behind the lens. You'll see the rays converge and diverge. I guess you could measure it with a metaltape. 

 forgoten says:  Dec 19, 2009. 6:56 PM  REPLYI'm wondering, if you use a rear projection TV for the source of the lens, couldn't you just measure the distance of the lens to the projector? or would that notwork? thank you for your consideration

 DrSimons says:  Dec 19, 2009. 10:28 PM  REPLYPossibly, but projection TVs tend to have 3 different projectors - one for each color. This, combined with the fact that they also have a large mirrorinvolved, makes it rather impractical I'm afraid.

 forgoten says:  Dec 20, 2009. 11:02 AM  REPLYthanks for the feedback. i'm kinda sorry that i cant do it the lazy way :(

 Moal says:  Sep 26, 2009. 6:58 AM  REPLYwill a 21 inch crt screen do the work. i have one broken at home. tell me cause i don't want to lose time to go and search for bigger screen. actually 39kmaway from my house there is a huge stockpile of broken tvs with good lenses about 10*10*10metres height of broken tvs all types of tv

 pindalanderz says:  Aug 27, 2009. 5:53 AM  REPLYpeople have been telling me that the tv will blow up if anything breaks. is this true and what can I do to alter this?

 DrSimons says:  Aug 29, 2009. 11:07 AM  REPLYNo that's crazy talk. If the TV was a CRT (the old kind with the glass tube) it would implode when you broke it....not exactly the same thing. But youneed a projection TV to get a fresnel lens, which just has regular air inside when you open it up. There are 3 small CRTs in a projection TV, but they'renot much of a hazard and you don't need to mess with them anyway.

 pindalanderz says:  Aug 29, 2009. 12:44 PM  REPLYthe tv I tried was a crt and it didn't even implode when I broke it. I took it out of the casing and snapped off the back. the only thing that happened wasthere was a black blob on the screen. I disposed of everything because I am currently not obsessed with this anymore. I know it was a crt because onthe inside of the casing it said it would implode if it broke. I think it just has to be plugged in.

 DrSimons says:  Aug 29, 2009. 1:17 PM  REPLYHmm. If it was an old TV, it's possible the tube had already leaked. It wouldn't matter if it was on or off though, the reason it implodes is thevacuum in the tube, which is always there. Also, could just be that the implosion wasn't very dramatic. It isn't a fusion warhead going off, just airflowing in rapidly, and possibly the glass breaking.

 joat_mon_99 says:  Aug 23, 2009. 1:47 AM  REPLYWhen taking apart the rear projection TV to get the fresnel lens, you should notice a projector array as well, be sure to remove that, or at least the lensesthemselves - the lenses are usually black plastic tubes with 3 lenses inside (in some cases you may have to break the lens housing to get them out. In theones I've got, the two end lenses are plastic, and are not suitable for use in this project, inside the casing, the middle lens is glass, mine is about 3inches indiameter. Pop that out and it can be used to further focus the fresnel beam. In may case there were also steel mounting brackets between the bottom of thelens assembly and the CRT projection tubes. (also, when you take these off, you will likely have to drain the optical fluid from on top of the CRT - this isethylene glycol, a coolant with the interesting property of having the same refractive index as glass. I recommend draining it into a clean container andsaving it for other uses.) If you remove and save those, they make a nice frame to mount your glass lens to your fresnel deathray project.

 d-sier says:  Dec 28, 2007. 2:20 AM  REPLYWhen you heat copper you make it soft, very useful when you want to shape it (without cracking it). Its used on most metals, the tell-tail of copper is that itchanges color when you do it. (If I remember correctly the color change is because you burn away the outer corrosions) if you want to make it hard again youheat it again and then cool it quickly (drop it in cold water). Try hitting it and a un-heated coin with a hammer and you will see the difference ;)

http://www.instructables.com/id/Giant-Fresnel-Lens-Deathray-An-Experiment-in-Opti/

 aleksei says:  Aug 8, 2009. 7:11 PM  REPLYyou're talking about work-hardening, right? I just learned that in metal working.

 NewDLee says:  Jul 17, 2009. 10:30 PM  REPLYAlso the layer under the charr of a copper sheet is photovoltaic! Home-made solar panels anyone?

 jfb1 says:  Jul 26, 2009. 10:01 PM  REPLYSharp rear projection TV, 50" fresnels are not very clear.

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