Fresnel lens report [Archive] - Glock Talk

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emt1581
03-25-2012, 18:05
Last week I ordered half-dozen of the 4x credit card sized fresnel lenses on ebay. Cost me around 4 or 5 bucks I think. Now I know many order them a hundred at a time but this was just to test them...

They came with clear covers and the first thing I did was take it outside to give it a try. It was a nice sunny day today.

First I tried it with the cover on just to see what would happen. It wouldn't focus the light right.

Took the cover off. Within two seconds of focusing the light the twig I focused on was smoking a lot. Then I used a long thin piece of bark. Same thing, after a few seconds it was smoking. But it burned a hole right through it instead of catching fire. I tried to angle the bark so that the flame might travel up...same thing...it was like a laser beam. I guess that is pretty much what it is.

So how do you actually light a fire as opposed to burning holes??

I'm guessing you need to have a pile or something like that.

Thanks

-Emt1581

Bolster
03-25-2012, 18:12
EMT, I'd try this myself if the sky weren't completely clowded...

Try focusing on a bit of dryer lint mixed with vasoline, see what that does?

quake
03-25-2012, 18:13
De-focus it somewhat, so the light is covering more surface area on the tinder. The fact that it burns thru like a torch is actually a good sign - means you've got more power than you need to start a fire; just need to disperse that energy over slightly more area, so it ignites the tinder rather than cutting thru it. Either de-focus it some, or use a tinder with more mass, like thicker bark or a twig.

emt1581
03-25-2012, 18:14
EMT, I'd try this myself if the sky weren't completely clowded...

Try focusing on a bit of dryer lint mixed with vasoline, see what that does?

I see what you're saying but I'll have the lens in my wallet...not lint and vasoline.

I'm more curious how you set any dry material (wood/paper/cloth/etc) on fire.

Thanks

-Emt1581

emt1581
03-25-2012, 18:16
De-focus it somewhat, so the light is covering more surface area on the tinder. The fact that it burns thru like a torch is actually a good sign - means you've got more power than you need to start a fire; just need to disperse that energy over slightly more area, so it ignites the tinder rather than cutting thru it. Either de-focus it some, or use a tinder with more mass, like thicker bark or a twig.

Oh ok, I'll give that a try.

It'd be interesting if this could be used as a laser could across a hundred yards or so...but with fire setting/cutting ability... But I know with a small piece of plastic I'm asking waaay too much here. :supergrin:

Thanks!

-Emt1581

Commander_Zero
03-25-2012, 19:38
If you really wanna go nuts, get the superlarge lenses...the ones that are a few feet across...they'll vaporize concrete. YouTube has plenty of videos of people melting padlocks, incinerating Spam, and that sort of thing. Isn't too hard to figure that with the proper lens and a frame you could make a solar hot water heater of impressive power.

Chindo18Z
03-25-2012, 22:48
Fire starting?

I just keep the damn thing in my wallet for reading fine print and maps! :supergrin:

Try using some finely crushed dried grass or powdered leaf/pulverized wood tinder...

Or a bit of pine sap impregnated lighter knot...

Or gunpowder (out of a cartridge from which you have pulled the bullet). Gunpowder placed in a wind protected pile under the edge of a larger tinder pile.

Bolster
03-25-2012, 23:00
I see what you're saying but I'll have the lens in my wallet...not lint and vasoline.

I must be odd. I carry a straw tube (sealed) with lint/vasoline mix in virtually everything from wallet to GHB to vehicle glove box. Takes almost zero space. If we ever get any sun here I'll give it a try. Interested in your experiments, good luck with the defocus technique, tell us how it goes.

lawman800
03-25-2012, 23:03
I see what you're saying but I'll have the lens in my wallet...not lint and vasoline.

Keep a pocket full of lint and a squeeze tube of vaseline in your jeans and you'll be set.

DJ Niner
03-26-2012, 00:46
The gunpowder thing works really well, but it's not exactly renewable/natural material.

For normal natural tinder (wood shavings, bark, etc.) you need to blow some air on it to get the superheated material to go from smouldering ember to flame. If the tinder is too light, you'll literally blow it away if you're not careful. Gentle, continuous airflow like you would use to whistle, with as few breaks as possible (keep'em short) until the ember grows enough to flame/flare-up. It's best to have the rest of the fire base wood pre-constructed, so you can just shove the flaming tinder into a hollow area at the base of the fire to get it going.

Should be plenty of primitive fire-starting vid clips on YouTube; watch a few to get the idea.


.

pugman
03-27-2012, 13:09
Keep a pocket full of lint and a squeeze tube of vaseline in your jeans and you'll be set.

Until the first time you have to explain why you have a tube of vaseline and a pocket full of lint to someone. :supergrin:

"Seriously honey its a fire starting kit"

I am a sick, sick man

lawman800
03-27-2012, 21:12
Until the first time you have to explain why you have a tube of vaseline and a pocket full of lint to someone. :supergrin:

"Seriously honey its a fire starting kit"

I am a sick, sick man

I'm sure there are worse things to carry around... like a rope, blonde wig, and petroleum jelly.