Giant Fresnel Lens Deathray: An Experiment in Optics
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step 2Build a Frame
The 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 a frame. 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 the lens against anything.
Materials Required:
The 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. By lowering 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 Frame
Once 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 on the 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.
Assembly
Once the frame pieces are positioned around the lens you can pull everything together. We sandwiched each corner between two pieces of plywood and put screws through 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 you could 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 you can 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 set your house on fire! Once again I am not liable for anything, including forest fires, so use your head.
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 the lens against anything.
Materials Required:
- At least 15 feet of lumber - I recommend 1x2" boards
- Plywood or misc. scrap wood
- 20-40 wood screws
- Power drill
- Tape measure & pencil
The 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. By lowering 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 Frame
Once 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 on the 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.
Assembly
Once the frame pieces are positioned around the lens you can pull everything together. We sandwiched each corner between two pieces of plywood and put screws through 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 you could 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 you can 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 set your house on fire! Once again I am not liable for anything, including forest fires, so use your head.
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