#284115 - 03/30/17 08:08 PM
Re: Using a lens to start a fire
[Re: Roarmeister]
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Geezer in Chief
Geezer
Registered: 08/26/06
Posts: 7705
Loc: southern Cal
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Actually, a hand lens for starting fire is not a prominent part of my plans. You need fairly robust sunlight to be successful, and that is not likely to be a situation where fire will be critical. Or to put it another way, when i have really needed a fire, it was after sunset, overcast, cold, etc.
Still, it is a worthwhile option, presuming one can plan ahead. It's been a long time since high school physics, but I daresay you are correct.
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Geezer in Chief
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#284116 - 03/30/17 08:57 PM
Re: Using a lens to start a fire
[Re: Roarmeister]
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Old Hand
Registered: 08/10/06
Posts: 882
Loc: Colorado
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I tried it last summer with a small hand lens.
Fail.
Even at 9,000' on a sunny day it failed. Atmosphere wasn't very clear due to forest fire smoke and I had difficulty holding it steady enough long enough.
More practice would be helpful I'm sure but it just doesn't seem worth the effort.
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#284117 - 03/30/17 09:28 PM
Re: Using a lens to start a fire
[Re: unimogbert]
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Geezer
Registered: 06/02/06
Posts: 5357
Loc: SOCAL
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A second Bic lighter is a better back-up IMO.
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#284119 - 03/31/17 03:02 AM
Re: Using a lens to start a fire
[Re: Roarmeister]
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Carpal Tunnel
Registered: 04/28/10
Posts: 3148
Loc: Big Sky Country
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I keep a credit-card-sized fresnel lens in most of my kits. As hikermor points out when you most need a fire it will least likely to work but I have used them to remove splinters, read small print on medicine bottles, etc. A fresnel is great since it's light, flat, flexible and very durable.
_________________________
“I'd rather have questions that cannot be answered than answers that can't be questioned.” —Richard Feynman
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#284120 - 03/31/17 05:28 AM
Re: Using a lens to start a fire
[Re: Phaedrus]
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Addict
Registered: 05/23/08
Posts: 474
Loc: Somerset UK
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A short focal length/high magnification lens has the slight advantage that it needs to be closer to the tinder. In most circumstances it is easier to hold the lens steady and at a short distance than at a longer distance. The actual light gathered is indeed in proportion to the area and not the magnification.
I have started fires in very marginal conditions by use of a large Fresnel lens, the smaller credit card sized ones only work reliably in ideal conditions IME.
As has already been posted, a fire is most needed in conditions when a lens is useless. Still worth carrying though IMHO, each fire started thus is one more match left for less favourable conditions.
A large Fresnel lens, say A4 sized will start fires in unfavourable conditions and is worth stocking in a long term TEOTWAWKI kit, but is unlikely to worth carry in a backpack.
In good sunlight an A4 Fresnel lens will light a fire of large sticks without any need to procure tinder.
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#284121 - 03/31/17 12:14 PM
Re: Using a lens to start a fire
[Re: Phaedrus]
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Carpal Tunnel
Registered: 05/05/07
Posts: 3601
Loc: Ontario, Canada
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I keep a credit-card-sized fresnel lens in most of my kits. As hikermor points out when you most need a fire it will least likely to work but I have used them to remove splinters, read small print on medicine bottles, etc. A fresnel is great since it's light, flat, flexible and very durable. Failing eyesight is the main reason I keep one in my kits too, Phaedrus. They are fun for firecraft practice but I wouldn't want to depend on that method in an emergency. Sidenote: a Fresnel lens and a pencil sharpener are a fun way to introduce kiddos to fire-making.
Edited by bacpacjac (03/31/17 12:16 PM)
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#284122 - 03/31/17 10:06 PM
Re: Using a lens to start a fire
[Re: Roarmeister]
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Carpal Tunnel
Registered: 11/09/06
Posts: 2846
Loc: La-USA
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Sidenote: a Fresnel lens and a pencil sharpener are a fun way to introduce kiddos to fire-making. wink
Jacque, I just put together 4 survival themed geocaches. I never thought about a magnifying hlass but included a pencil sharpener for the enclosed pencils (graphite won't run if it gets wet) and as fire starter material.
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QMC, USCG (Ret) The best luck is what you make yourself!
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#284124 - 03/31/17 10:15 PM
Re: Using a lens to start a fire
[Re: adam2]
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Carpal Tunnel
Registered: 05/05/07
Posts: 3601
Loc: Ontario, Canada
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As has already been posted, a fire is most needed in conditions when a lens is useless. Still worth carrying though IMHO, each fire started thus is one more match left for less favourable conditions.
I've never thought of it that way, Adam. I like your thinking. Thanks!
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#284126 - 04/01/17 03:43 AM
Re: Using a lens to start a fire
[Re: adam2]
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Carpal Tunnel
Registered: 04/28/10
Posts: 3148
Loc: Big Sky Country
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I have started fires in very marginal conditions by use of a large Fresnel lens, the smaller credit card sized ones only work reliably in ideal conditions IME.
As has already been posted, a fire is most needed in conditions when a lens is useless. Still worth carrying though IMHO, each fire started thus is one more match left for less favourable conditions.
A large Fresnel lens, say A4 sized will start fires in unfavourable conditions and is worth stocking in a long term TEOTWAWKI kit, but is unlikely to worth carry in a backpack.
In good sunlight an A4 Fresnel lens will light a fire of large sticks without any need to procure tinder.
Very true. I do have some A4 Frensel lenses around but I don't carry them as part of my survival gear. As you say, probably good as long term preparedness items but to me a little bulk and impractical to carry vs the likelihood of use. When I most need a fire there often isn't any sun to begin with. I will say though that fire making is one of the areas where I have the most gear on me. When I'm out on hikes and camping trips I will generally have at least two firesteels, a minimum of two lighters (one peanut-style and one Bic, and I'll note that I don't smoke), and UCO Stormproof matches. Very often I'll also have a Spark-lite and I always have a variety of tinder/fuel items (including Hexamine tablets, fatwood and Tinder-Quik tabs).
_________________________
“I'd rather have questions that cannot be answered than answers that can't be questioned.” —Richard Feynman
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#284127 - 04/01/17 04:03 AM
Re: Using a lens to start a fire
[Re: Phaedrus]
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Geezer
Registered: 06/02/06
Posts: 5357
Loc: SOCAL
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No pencil sharpener? They make great tinder.
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#284129 - 04/01/17 04:38 PM
Re: Using a lens to start a fire
[Re: Roarmeister]
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Carpal Tunnel
Registered: 11/13/06
Posts: 2946
Loc: Nacogdoches, Texas
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I don't think I've done this since I was a child; I had no trouble getting a leaf to burn by simply using my glasses. Jeanette Isabelle
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