Giant Fresnel Lens


I found a company that sells giant fresnel lenses. What is a Fresnel lens? Think of a lighthouse or the top of an overhead projector. As light goes through the lens, spiral cut ridges focus the light to a focal point. You end up with the equivalent of a giant magnifying glass or parabolic mirror. There is some really juicy math invovled in calculating how to create a lens, determining the focal length and lens strength.


I framed the lens with some 2“x2“ lumber and secured it with electrical tape. When I carried the lens out of the garage, I knew we were in for a good show. The asphalt driveway started smoking. Our first target was a penny which the lens quickly melted into slag. Next up was a hamburger. We widened the focus and it flash cooked the top of the burger.


 


What I learned:



  1. You really need welding goggles. I have none so we had to use a spotter from a distance to help us focus. If you knelt down and tried to focus it without eye protection, you would surely suffer eye damage.
  2. If the sun is directly overhead, the lens is easier to focus and burns significantly hotter.
  3. Burgers cooked with a giant death ray don't taste very good. It's about like cooking in a microwave: you don't get the smoky taste that a BBQ gives you.

 


Comments (31)
  1. DEATH RAY OF DOOM … hmm there’s an ebay slot for those I’m sure! 😉

  2. Sushant Bhatia says:

    LOL Giant Death Ray of DOOM. This would make a nice fatality for Sub Zero in MK. 🙂

  3. Sushant Bhatia says:

    OH man I just saw the website. Their "scientist" look like Unix users.

  4. Brian Keller says:

    Wow this is the second post I’ve read about fresnel lenses in the past few months. It’s a good thing blogs hadn’t been invented when I was twelve for the sake of my local fire department and my retinas!!!

  5. SimonTocker says:

    What on earth are you going to use it for, apart from comedy value ?

  6. Nick Veitch says:

    I wouldn’t wear sandals whilst weilding the thing if I were you…

  7. Jeremy Rule says:

    Simon: I use it just for fun. There are practical uses though. I know Nasa has a big one in space. Also consider you have a lightweight oven that can cook stuff with no fuel. That’s pretty cool.

    Nick: I beg to differ. A science experiment isn’t any good (or fun) unless there is an element of danger. Potato guns, flame throwers, big chemical reactions — that’s the good stuff!

  8. It would be cool to see if you could get it to run a little steam turbine. Micro-solar power.

  9. Andrew says:

    Probably wreaks havoc on dogs too.

  10. What?! No Ants!? 😉

  11. Sam says:

    Whats the range of those things? (Could I for example mount one on my car…?)

    lol

  12. science fan says:

    as for point #3 – this still might be a fun way to *start* the barbeque for those who don’t have liquid oxygen as an option [ http://ep.llnl.gov/msds/Chem120/lox-oxidation.html ]

  13. Paul McBride says:

    Jeremy:

    I got your IM but was not at home. "Old Rugged Cross" sounds good. Do you have the sheet music or MP3? I’ll get cracking.

    -Paul

  14. Anonymous says:

    TinyScreenfuls Trackback

  15. Kai says:

    sooo cool … I am off to get me one…

  16. Eugene says:

    Say, WHERE can I buy this GIAN FRESNEL LENS?? Please give me the URL! THANKS!! Eugene

  17. John says:

    I would love to find out where to buy these also. Please let us know. Thansk!

    John

    john@airwired.net

  18. Jeremy Rule says:

    Guys there’s a link right in the first paragraph of the post to alltronics.com.

  19. Brian Noyes says:

    You didn’t mention one of the cooler uses of fresnel lenses: bringing our trusty naval aviators back aboard the carrier on every landing. The "meatball" or "ball" as it is called is an array of fresnel lenses that provide precise visual glideslope information to the pilot from a gyro stabilized platform so that even with pitching decks they can fly down the perfect glideslope to an "OK" 3-wire.

  20. Vince says:

    If you want some more information on Fresnel lens applications and other solar uses, check out this site. http://www.knowledgepublications.com. The guy sells smaller 8.8 x 11 fresnel sheets and has some intersting books on solar power and hydrogen stuff.

    Cheers

  21. Aaron says:

    I bought a 3′ X 3′ fresnel lens from Edmunds Scientific years ago when I got a catalog. Right after I bought it, I went on vacation in florida during the summer and created a rotating mount for it so I could track the sun. Put a holder on it at roughly the focal point and cooked all sorts of things. Burned quarters (for some reason they only burned, not melted…) melted pennies, boiled chocolate water (wonder if you can create a solar steam engine?

    I couldn’t leave the mount in the sun when I took a break, because being made of wood, it started smoking the base of the stand I had built, which was a couple of inches beyond the focal point.

    I agree with the welding goggles. I wore *two* pairs of *very dark* sun glasses and still found myself only looking at the focused sun for a second or two at a time because it was so bright!

    I also burned asphalt with it, and cracked and powdered concrete.

    I still have it, and every summer dream of creating a solar steam engine, or a solar powered grill. I am sure that you really could create a solar steam engine to power an air conditioner compresser in Florida with a couple of these babies and some mirrors to get the solar power where you want it!

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