Magnifying glass fire

S

Scottman

Joined
Jun 24, 2007
Messages
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I have one of those frensel magnifying sheets, the size of a credit card. I decided to test it, its in the doug ritter survival pack, and I couldn't get a fire going. I tried it on birch bark, got lots of smoke, but no flame. I blew on it while doing this. Nothing. The sad part is I remember starting fires as a kid with a magnifying glass, and now I can't do it. :confused: Anybody got some suggestions?

Thanks,
Scottman
 
Hey Scottman...

Have you tried it using some char cloth ??

If Doug has put it in a kit then it will work...

You may also want to pick up a small glass magnifying glass at the dollar store and compare the two..

Make some char cloth and get some Jute cord...That will for sure work...

ttyle

Eric
O/ST
 
Although I have only rarely had success I do have some pointers I picked up somewhere. Mostly, your tinder is critical. It has to be the lightest, fluffiest stuff you can find. Even something like cottonballs should be pulled apart, and fluffed. Also, the more edges or angles you have, the better. It is easier to start a fire on the edge of a piece of bark than it is in the middle of a sheet. Lastly and perhaps the most difficult is focus. You have to get the smallest possible "dot" of light and it must be maintained in the exact same spot as long as possible. Both of these can be difficult when the lens is being held by hand. I am no expert but I hope this helps. The fact that you were generating smoke leads me to believe you were at least on the right track.
 
remember that light colored objects absorb less light energy and tend to reflect it. i would dye cotton balls a dark color or use dryer lint since its fluffy and usually dark. you can make an emergency magnifying lens with some plastic wrap and water. all you need is something to make a hoop to drape it over. just remember, the thicker the lens, the hotter the focal point.
 
I have a 10X mag. mirror that I got for about $3 at Wally in the cosmetics dept. It is a mean mutha for firestarting, plus you can check your face & neck for ticks and such, and use it to help get debris out of your eye. The concave shape may hinder it as a signal mirror somewhat, but the benefits greatly outweigh that one possible problem. :D
 
I recently started a fire with a magnifying glass by using a sliver of wood from a railroad tie. I got the pointy end of it to turn into a coal and then wrapped my tinder around it and it blew right up into a flame. Mac
 
For starting a fire using a lens,of course charcloth will catch in only seconds,but I have had success with several natural materials as well,finely shreded and flufed up poplar and cedar bark work well,and I find it helps to char a .25in circle or so with the lens in the bark before trying to get fire.
Also very dry rotten wood works well,it can be blown into flame and holds an ember for a long time.Several types of dry grass also work well,I usually make a small "nest" of really shreded material and put that in a larger nest of courser material.

Hope this helps,
loto
 
richard j said:
remember that light colored objects absorb less light energy and tend to reflect it. i would dye cotton balls a dark color or use dryer lint since its fluffy and usually dark. you can make an emergency magnifying lens with some plastic wrap and water. all you need is something to make a hoop to drape it over. just remember, the thicker the lens, the hotter the focal point.
Click to expand...

richard j is absolutely correct about the colour. To convince yourself, try lighting the paper on the side of a cigarette (nice and thin, should light easy - doesn't), then try the end, directly on the tobacco.

Doc
 
Tried the same thing yesterday with an SAK magnifying glass.

In addition to dried grass, I used a few strands of saturated cotton ball as well. No luck.

Will try the char cloth this weekend. Thanks.
 
When focusing (focussing???) the dot, you might notice that moving slightly out of focus one way gives a blue/purple shade, the other way gives red/orange.

That's because a simple lense focuses different wavelengths at different distances (sorry for the science 101)

The point is that that infra red is best for firelighting (it *is* thermal radiation). So, if you focus slightly on the red side of focus, rather than in the middle, it works better because the red/infra-red is concentrated more. That's my theory anyway, and I've backed it up experimentally as well.

Works for me! And that's in flooded England!!!

Rick.

Rick.
 
foxyrick said:
When focusing (focussing???) the dot, you might notice that moving slightly out of focus one way gives a blue/purple shade, the other way gives red/orange.

That's because a simple lense focuses different wavelengths at different distances (sorry for the science 101)

The point is that that infra red is best for firelighting (it *is* thermal radiation). So, if you focus slightly on the red side of focus, rather than in the middle, it works better because the red/infra-red is concentrated more. That's my theory anyway, and I've backed it up experimentally as well.

Works for me! And that's in flooded England!!!

Rick.

Rick.
Click to expand...



Rick is correct. IR focuses at a slightly different point then visible radiation. Slightly in front IIRC. Practically I'm not sure how much of a difference this will make (because I believe the difference to be very small) but it doesn't hurt. :D

KR
 
kr1 said:
Rick is correct. IR focuses at a slightly different point then visible radiation. Slightly in front IIRC. Practically I'm not sure how much of a difference this will make (because I believe the difference to be very small) but it doesn't hurt. :D

KR
Click to expand...

I found it made quite a difference. Trying out on grey card (inside cerial packet): focusing slightly on violet it barely smouldered; centre-focused it started to smoulder; red-focused it smouldered much quicker. All were held in that focus for about 5 seconds in strong sunlight, with a steady, supported hand, on different (i.e. cool, not already charred) places. Not truly precise, but definately enough to show a reasonable difference. The lens is 4 inch diameter with a focal length of about 9 inches.

It's an easy one for people to try out for themselves.
 
Thanks everybody. I guess when I tried it in my youth it must have been a dry summer and everything must have been "tinder dry".

I got a fire going today. I took my dozier and scraped it perpendicular to a cedar tree. It was on a south facing slope so it was pretty dry. Got nice fuzzy cedar bark tinder, about the size of a golf ball. I put some slivers of birch bark in this little "nest" . I reclined down next to this and focused the rays on the cedar bark. A coal started to grow, I gave it some air, and suddenly, FIRE. :)

This little frensel thing is pretty good for its size. I might go get a magnifying glass to compare it to.

Scottman
 
My 10 year-old son got two days of detention for bringing a magnifying glass to school and using it--unsuccessfully-- on a pile of dried leaves. His principal and I went round-n-round over his detention. She contended that "if" he had started a fire, he would have put other students at risk. My contention was there was no way in Hell he was ever going to be able to start a fire using that magnifying glass because he was physically unable to hold the glass in the correct position long enough to get more than some light smoke. I knew this because I was the one that taught him how to use a magnifying glass and had seen him struggle for an hour or more with no better results. I told her she should be patting him on the back for exercising his scientific curiosity. Needless to I lost the argument and my son learned a good lesson; some things you know are better kept to yourself. :)
 
Texas Slim said:
My 10 year-old son got two days of detention for bringing a magnifying glass to school and using it--unsuccessfully-- on a pile of dried leaves. His principal and I went round-n-round over his detention. She contended that "if" he had started a fire, he would have put other students at risk. My contention was there was no way in Hell he was ever going to be able to start a fire using that magnifying glass because he was physically unable to hold the glass in the correct position long enough to get more than some light smoke. I knew this because I was the one that taught him how to use a magnifying glass and had seen him struggle for an hour or more with no better results. I told her she should be patting him on the back for exercising his scientific curiosity. Needless to I lost the argument and my son learned a good lesson; some things you know are better kept to yourself. :)
Click to expand...


Your sons principal is another in a long line of half wits who we are allowing to run our schools and turn our kids into automatons. But this is a different discussion.

Christ! When are they going to start registering those damn magnifying glasses. Its all fun and games until someone losses an eye, or some idiot principal overreacts. :barf:

KR
 
When I was in school, around 7-8 years old, a lot of the kids were into carrying lenses for assorted heat-related uses. Some liked to melt the rubber on their shoes, others chased ants, I started fires, the dumber kids would burn their hands and the bullies burned other kids' hands.

I don't think the staff ever noticed or cared.
 
Although I have had some success with different lenses, I've never been able to do it with a SAK magnifier. Anybody get a SAK lens to work?
 
I've alwasy thought of a SAK magnifying glass as a tool to read map detail or look for a splinter. It's pretty small for fire-starting.
 
When I was a kid I had a really large Fresnel lens. I think it was about the size of a sheet of paper. . . 8 1/2 x 11 or so. That think would set anything on fire. . . even bright white paper. . . in just a few seconds. Something that size wouldn't be practical for a portable kit, but it might be handy to have at home.

Edit: This would be fun to play with too: http://cgi.ebay.com/53-grande-FRESN...9QQihZ008QQcategoryZ48655QQrdZ1QQcmdZViewItem
 
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