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."

Comments

Re:Mindless

[DoraLives]

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.

Yeah, and I guess it shouldda been Smiley Captioned for the Humor Impared, too.

...and?

[Sycraft-fu]

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.

Re:Mindless

[Cecil]

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. ... you say that like it's a bad thing?

Re:Would this be possible?

[pedantic bore]

It wouldn't work as a laser per se, because the light would not be coherent. Only the light beams that are more or less parallel to the end of the fiber would find their way through the cable (although this could be increased with a few more lenses along the way).

As far as the fresnel-lens-in-space idea is concerned, it scares the crap out of me. If the thing gets knocked out alignment (maybe dinged by some of the tons of space junk already in orbit you suddenly have a death ray tracing random patterns across the planet, with no off switch (short of destroying the lens).

Re:Ideas

[timmi]

It's more efficient because it's cheaper. the chost prohibitive compinent of the system os the solar cell, whereas the lens and the litle bit of mechanics to keep it aligned is relatively cheap, (or at least that was the case when the idea was widely talked about)

The Voice Of Experience, '72

[cmholm]

Ah, jr. high science fair. Back in '72, Edmunds' lens was only about 1.5' square. I found a design for a 4' tall wood test rig at the library, which wisely suggested a kiln brick at the focal point. I chiseled out a small pit to hold samples, and went to work.

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.

Re:Ideas

[jd_esguerra]

Right. A smaller cell that could absorb the focused light would be more efficient and probably cleaner and more efficient to produce or operate. The issue I was addressing is that you can't really increase the output from the solar cell because you are still limited by the amount of light entering it. Consider this: A flashlight (with beam having a low divergence angle) is shining on a large perfectly efficent solar cell. All of the light is converted to energy. If the same (wide) beam is focused down to a perfecly efficient solar cell that is 1/100 the area of the larger cell, you will see the same energy. To obtain the full energy of the flashlight's beam, the lens would have to be at least as big as the beam cross section at their intersection in space. A cell of that same area as the lens would (theoretically) receive the same power from the flashlight.

So I agree with timmi. But remember that the ore optics you have in your system, the less light will reach the photovoltaic cell. Optics are not perfect. (By the way, mirrors are lighter than lenses, and are easier to build and control.)

Re:Nice picture of a giant fresnel lens in action

[drinkypoo]

He in fact is a very neat guy. He is typical of the old school Santa Cruz geek, which is to say he is atypical and good-natured and -hearted. At least, far as I can tell.

I've known or been around a number of geeks who worked for SCO in the old days, and they were all really cool, knowledgeable people. And, I've been sloshed at the Armory a few times. :)

Re:Mindless

[drinkypoo]

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.

concrete: "A hard, strong construction material consisting of sand, conglomerate gravel, pebbles, broken stone, or slag in a mortar or cement matrix."

I do not think that word means what you think it means. It seems as if you are confusing concrete with asphalt or tarmac(adam).

Guess what, setting shit on fire is fun! If you are relatively responsible about it and don't light shit on fire accidentally and/or let things get out of hand (note: many forest fires grow from the cooking campfires of the incompetent) then really, who are you harming? Well, anyone breathing the vapors. But besides them?

Re:Ants

[togtog]

I cannot see a mod, regardless of how trollish, modding this Redundant and not funny, so either it was a mistake or someone is really smoking the crack. Just my non-annoyamouse 2 bits.

Re:Archimedes

[WillWare]

The I heard it, he didn't use lenses, he used mirrors. He got the army to issue polished metal shields to all the soldiers, that could be used to cast shield-sized reflections onto the sails of approaching ships. If all the soldiers put their reflections on one spot on the sail, it would set the sail on fire.

I think you're right that this story is probably apocryphal. It's hard to imagine that good mirrors would have been inexpensive enough in those days to make this practical. It's also difficult to imagine how they got coordinated enough to get all the reflections onto one spot.

Re:Mindless

[Invidious]

You've never gotten a caustic burn, have you? Naw, you're just repeating what you've heard.

Lemme tell you, you can feel the burn from alkali materials. It doesn't "just eat through your skin." First, it makes your skin slippery as it interacts with the upper, dead layers of your skin. Then, as it starts to get into the living layers, it starts to itch. That's about as far as has happened to me, but after it starts to itch, it starts to burn. Then you've probably got some real damage.

Re:Avoid antabuse at all costs

[Anonymous Coward]

Considering that the reaction can severely injure or kill the person taking antabuse, regardless of whether he/she had any intention of driving drunk, I'd say that it shouldn't be involuntarily administered to anyone.

Seriously, something that turns a commonly available substance that the person is likely to want to ingest into a potent poison is definitely not a good idea. I'd be surprised if you could find many ethical doctors willing to endorse such a "treatment".

Re:Ants

[Reziac]

How can I buy a solution if I'm insolvent? ;)