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AndrewS
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Posted: 9/22/2007 9:06:32 PM
Due to their compact size I figured one would make a perfect pocket magnifying glass to use for fire starting. Has anyone tried it before?
LadyMacBeth
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Posted: 9/22/2007 10:14:06 PM
size counts in solar fire starting focal length is not as important, we have 2x3" pocket mags and 8x11" frenel sheets, we don't count on them because we get little sun when we need fire but they are light and don't take much room.
qwijibo
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Posted: 9/23/2007 6:54:25 AM
Try it before you rely on it. Now I have something else to do when the sun comes up since I have a set of loupes on my desk.

However, I would strongly consider fresnel lenses. I have tried those before and the business card sized ones can be used to start a fire reliably with some effort. The 8.5x11 sized ones (as thick and heavy as 5-10 sheets of paper) will start wood on fire pretty quickly without the need for tinder. It will start things like cardboard/paper in fire in a matter of seconds. I put one of each in my packs. They weigh nothing and cannot be beat for their ability to get a fire started with the sun. They're also on the order of $2-10/each depending on where you get them.
AndrewS
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Posted: 9/23/2007 5:59:40 PM

Originally Posted By qwijibo:
Try it before you rely on it. Now I have something else to do when the sun comes up since I have a set of loupes on my desk.

However, I would strongly consider fresnel lenses. I have tried those before and the business card sized ones can be used to start a fire reliably with some effort. The 8.5x11 sized ones (as thick and heavy as 5-10 sheets of paper) will start wood on fire pretty quickly without the need for tinder. It will start things like cardboard/paper in fire in a matter of seconds. I put one of each in my packs. They weigh nothing and cannot be beat for their ability to get a fire started with the sun. They're also on the order of $2-10/each depending on where you get them.


I would absolutely try it first but I was hoping someone that already had them could try before I even bother to buy one.

Please let us know how it works out for you.
qwijibo
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Posted: 9/23/2007 7:33:02 PM
The loupes didn't work (tried 2x and 10x). The 8.5x11" fresnel lenses work very well, are inexpensive, and lightweight. For starting a fire with the sun, I strongly recommend them.
cmjohnson
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Posted: 9/23/2007 7:36:11 PM
Smaller lenses aren't as good for starting fires. The more light they gather, the more effective they'll be.

A four inch magnifying lens is very effective on any day where the sun is clearly visible and
can be used to start a fire on a somewhat hazy day. Smaller lenses need direct sunlight
to have a chance of starting a usable fire.

I have a rather cool 10 inch lens that can be used to start FOREST FIRES.

But it won't fit in your pocket!


CJ

Bloencustoms
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Posted: 9/23/2007 10:38:04 PM
[Last Edit: 9/24/2007 12:33:34 AM by Bloencustoms]
I've gotten cigarettes lit in full sun using a small plastic lens from an eyeglass repair kit. It works, but it's not the easiest. I have also lit one using a surveyor's theodolite. In fact, you ave to be careful with those instruments because people have started brush fires by leaving them set up where sun could focus through the lenses onto the ground.


ETA:

Anyone try a clear glass marble?
http://www.youtube.com/watch?v=Mnb4QmNJLKw Double Trigger AR15
AndrewS
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Posted: 9/24/2007 12:57:56 PM
I am glad I asked before dropping the coin then. I figured the larger the better but I wasn't sure what, if any, effect magnification would have.
SRM
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Posted: 9/24/2007 10:53:06 PM
I use a 7x and 10x hastings triplet regularly (I am a geologist). The lens diameter is similar to a AA battery. I used them to start a fire exactly once, but it also involved a water soaked paper match.

You need surface area to start a fire with a lens. An 8X10 frenel lens will easily melt lead on a sunny day and will start a fire in under 5 seconds.

SRM
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