Need advice - Starting fire with a Fresnel Lens.

Diomedes Industries

Diomedes Industries

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Mar 19, 2007
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I have had VERY good luck - or no luck at all with my Fresnel lens starting fire. I use a small card pocket magnifier and can get paper to smoke and burn a little - but not catch light.

I have practiced getting the dot of light to be as small as possible - but still little joy most of the time.

Any advice would be great.

TF
 
The object of using a fresnel lens is to get a coal you can nurture into flame. When you are getting smoke, try blowing on the coal in the bundle to catch a flame. Works for me.:thumbup:

Make sure you are getting the most focused beam you can get too.:thumbup:
 
Talfuchre said:
I have had VERY good luck - or no luck at all with my Fresnel lens starting fire. I use a small card pocket magnifier and can get paper to smoke and burn a little - but not catch light.

I have practiced getting the dot of light to be as small as possible - but still little joy most of the time.

Any advice would be great.

TF
Click to expand...

I'm guessing you're using it on white paper? To be most effective, you want to concentrate the point of light on something dark, the white colour reflects some of the heat. For example, years ago, when I used to smoke, concentrating the point of light on the white paper did little, but if I focused on the tobacco at the end - voila!

Doc
 
When you light paper with a match, where do you put the match?

At the edge and below the paper. Kinda hard to do with a small beam of concentrated sunlight.

That being said, I find fiberous tinder the easiest to light with a lens. I shoot the edge and slightly off the ground. Getting leaves (paper) to take flame is difficult (for me). Jute maybe a good tinder to practice with. Hope that helps, Chris
 
Take some char cloth and beam your light on it. Then take your char cloth into a bundle of grass and blow it into fire.
 
Always carry char cloth. Always. With any method this is the difference maker.
 
I use a small 10X concave mirror and find that a tight bundle of very fine, very dry tinder takes a coal the best. The more flatly you can apply the light the better. I wound some jute around a dry grass bundle very tight, and neatly cut the end off with my knife, and had a fire in about 1-1 1/2 min. BUT it was dead of summer, super hot and bone dry. I tried just lighting random tinder with bits of smoke, no notable coal, and no success. And my trusty PJ cotton balls were all but useless in this capacity. I think dark tinder does help.
 
I find that in addition to making a dark spot on a piece of paper, either with dirt, ash, or ink, that it is very helpful to fold the paper in half several times so that the coal can grow down into the paper. I usually make a burn about 1/4 - 1/2" in diameter, and then I burn down through several layers of paper. Pressing the edges of the glowing circle together while blowing gently will usually bring a flame right up. I keep the heat on while blowing, too. Every little bit helps. Newspaper works very well for me, because it already has dark patches, and it gets better the older it gets.
 
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Wax paper. Poof. Don't look at the spot too much in case it could hurt your eyes.
 
When I was a kid, I got a hold of a Fresnel lens from an old overhead projector. The kind of projector that was used in school to project writing from transparencies. It was about a foot across and would produce a spot the size of a half dollar, and you wouldn't need tinder, or char cloth. It would set fire to a 2x4.

I wouldn't imagine you'd want to carry one of those in the field, but damn, it was a lot of fun.
 
About the spot size of the magnifer...make as small a spot of visible light and then pull the back a little bit to bring the IR light into focus. You can't see IR light, but it's there and it has a slightly lower refractive index, hence a longer focal length for a given diopter strength of a lens. I've never done the calculation, but I seem to find by trial and error to pull away <= 10% of the distance for the smallest spot size to achieve the hottest spot. For a normal lens, that might be between 1/4 and 1/2 inch farther away from the tinder.
 
Never heard of using a Fresnel lens to start a fire.
Where are you finding a Fresnel that small?
Denis
 
I bought a couple of credit-card sized fresnel lenses years ago from an opticians - sold as 'pocket magnifiers'.


http://www.mapsco.com/searchresult.aspx?CategoryID=58
http://www.familytreefolk.co.uk/page_10946.html

Be aware that they scratch up quite easily, and can get dust and dirt in the grooves. Best to keep in the slip wallet and tape the end shut.

For the IR, I just pull back enough that the red light focuses (the spot turns red rather than white). It's close enough and works nicely.

I remember that an online scientific supplier sold a fresnel 'solar furnace' that was about 3x2 feet - I bet that could light some fires!

Remember: the bigger, the better. Magnification is irrelevant; what matters is light-gathering ability.

Finally, my favorite thing to light with light is a mixture of powdered potassium permanganate and sugar. It's dark and flames up very quickly! Only a small amount is needed along with a bit of wood to catch the flames from it.
 
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I would think neither a true Fresnel lense nor a flat "card" type could concentrate enough of a beam to be successful.
A conventional magnifying lens would most likely work better.
Denis
 
How can you concentrate on starting a fire when there are so many ants to fry ?
 
foxyrick said:
Remember: the bigger, the better. Magnification is irrelevant; what matters is light-gathering ability.
Click to expand...

firewithSAK2-forphotobucket.jpg


firewithSAK3-forphotobucket.jpg


Doc
 
Size isn't the whole picture, as noted. The lens configuration does matter, and a Fresnel (especially a flat one) is not the best type for that job.
Denis
 
DPris said:
Size isn't the whole picture, as noted. The lens configuration does matter, and a Fresnel (especially a flat one) is not the best type for that job.
Denis
Click to expand...

Actually you'd be surprised how well they work. (If you mean on paper then I agree with you. It does however work well on charcloth, coals, and other items.)

I've bought several at Barnes & Noble. (Not all of them carry them.)

Here is a couple of pictures I took after playing around with a fresnel.

175054248_9ff3e81673.jpg


175065106_a0aa753ee9.jpg


175054250_9c99bbef1e.jpg
 
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