Burning without using a laser...

[PocketBeam]

In some of the talk about creating a burning laser several people mentioned you could take a fresnel lens and focus sunlight to a point and burn or melt things.

Is it possible to focus the light down to a point and then redirect the pin point light at will. So in effect you have a daylight laser. (OK laser like)

It might be cool to have a black box (mystery box) that you put on your car roof and then from it you can point a beam that can start your camp fire.

Thoughts? Any one done something like this?

Maybe a parabolic mirror with a focus point of several feet might work?

 

[DaFiend]

wouldn't be easier to just use the lense itself? it would take up a hell of a lot less space and be alot more portable? /ubbthreads/images/graemlins/thinking.gif

 

[badhorsey]

It's possible but there are limitations. It would only burn at or very close to the focal point and you'd need the sun directly behind the lens for it to be effective. So in terms of directing it where you wanted, you'd be better off mounting a CO2 laser onto your car.

Not that I actually advocate that sort of thing. Ooh no.

 

[greenlight]

at a burning man party there was a fresnel lens mounted(3'x4') on a stand and people were burning stuff. They were melting pennies.
To get proper temperatures you need to have the right size lens and the time of day is important also.

The thing about starting campfires with a magnifyer is... the sun is usually setting when you are ready to have a fire, and the sun isn't as strong then. You never really need a camp fire at noon, when the sun is strong!

Nevertheless, I always have a magnifyer around for burning stuff. My magnifyer collection is as big as my flashlight collection.

 

[PocketBeam]

What about a fiber optic system to redirect the light?

I didn't know they made 3'x4' fresnel lens, where can you get one that bid for cheap?

 

[snakebite]

[ QUOTE ]
PocketBeam said:
What about a fiber optic system to redirect the light?

I didn't know they made 3'x4' fresnel lens, where can you get one that bid for cheap?

[/ QUOTE ]
look for junk projection tv's on trashday or behind tv shops.the screen is a freznel lense.

 

[greenlight]

I'm pretty sure you can get it online - it was for a solar furnace or something.

 

[snakebite]

another source is the one you see in the rear window of motorhomes.
i have a bunch of projection tv screens i saved for replacements of customers scratched/busted screens.
i will have to take one outside next sunny day and see what it can do.

 

[greg_in_canada]

I think the motorhome fresnel lenses are negative focal
length (de-magnifiers) rather than positive FL.

I would guess that surplusshed.com and Edmund Scientific
would have big fresnel lenses.

Greg

 

[PocketBeam]

I found this - Altronics

Check out about 2/3 down the page. Three different big fresnel lenses.

 

[Draco_Americanus]

I ran into problems with newer projection tv's as a source for fresnel lenes. it seems that newer tv's whon't foucus down to a tight spot but rather a wide line that can't generate the pop can cutting heat. I belive a tv with that lense has a better veiwing angle from the sides but from a pyro point of view are not as usefull. So one must experemnt if you run accross a junked rear projection tv and the older the better.