Fresnel lens?

Anyone have any experience using a plastic Fresnel lens to create a fire? If I were to purchase a sheet of this stuff to try, what do I need to look for? Is there much difference?

I started a fire in my back yard using leaves and paper. I used a 2 1/8" x 3 1/4" "ITOYA POCKELENS" fresnel lens I kept in my wallet for years. Bought it in a book store. Despite late 4PM sunshine I got a flame going without using tinder in about 10 seconds by just blowing on the smoking hole created by the lens. I have a larger one about 4"x6" but a sheet isn't necessary. BTW newsprint lights almost instantly.

It's a great backup or secondary survival fire starter since it takes no more room than a credit card. Of course you need to get the fire going before sundown. Perhaps the larger fresnel would allow one to start a fire closer to sunset.

The waller sized ones are kind of hard to start fires with. The big ones (notebook sized) are so easy it's ridiculous, those things are downright dangerous. However, when you need a fire the most, there's probably no direct sunlight available. You're better equipped with a more normal firestarter.

rodmeister,

What latitude are you at? I'm at 45 north (twin cities MN), and early last fall I gave firemaking a try with fresnel lenses, and didn't have much luck, and certainly not with the credit card sized ones.

A fresnel lens is useful if you bring a small survival handbook and normally need reading glasses. The lens can serve as a backup to your reading glasses. Their use as a firestarter is secondary.

I found one place to order them online: http://3dlens.com/

Yep thats my problem with them. When I need a fire its dark, dreary, cloudy, windy and rainy.

I carry a credit card sized one. In summer it works well. In the winter it mandatory to have the proper tinder. I found that fungi from tree work great. Once they start smoldering they keep going and when you blow gently the ember gets hot enough to ingite cotton or dry grass.
It´ll be a really hard day if I ever need to use it for firestarting as I carry enough other means for that purpose. I carry the lens as magnifying glass. Other poster already mention why.

Goatrider, I live in the Venice District of Los Angeles, CA, near the beach. I tried my experiment in winter at around 4PM. I was surprised how well the credit card sized fresnel worked. But I can understand it failing at high latitues, especially in the cold.

I will take my 4x6 inch fresnel at higher latitues. And you're right, I never count on it has a primary fire starter. I think everyone can agree on the foolishness of that. It's only for use as a last-ditch solution. I carry the card for presbyopia.. "old peoples eyes."

But I wouldn't use that as an excuse not to carry a card sized fresnel. It's a backup or secondary or tertiary fire source for when you lose your matches, lighter, flint, or whatever.

A backup should be reliable and possibly not fail for the same reason as the primary item. The fresnel lens lacks the reliability in most scenarios where you would need a fire. Maybe it would be better not to consider it as a fire source unless you have no choice or don´t actually need the fire promptly.
I second the advice to carry one though. I used mine for many purposes including first aid. The small size and weight are hardly noticeable and worth it.

I read somewhere on the web that it is possible to make a lens out of a clear plastic bag of water on a plate of glass or clear hard plastic sheet.

You supposedly fill the bag with clear water, put it on the glass plate in such a way that the bag is convex at the top while being flat on the glass at the bottom and concentrate the incoming sunlight in that manner.

Any one on here ever try it?

Bountyhunter

I did (note to myself: quit trying everthing you read on ETS).
The material:
- clear ziplock bag 3" x 6"
- lid of CD jewelcase
- 4 clothespins (I´m aware this is close to cheating)
- tap water

I fill the bag with some water and poured out some until the focal length was manageable. The bag was pinned to the lid with the clothespins. When the bag was filled to about one third I was satisfied. I found that air bubbles are no problem as they rise to the top where the geometry isn´t good anyway. The geometry of the lens deteriorates when it is tilted to the vertical. The focussing is not too good and the intensity is even worse than with the fresnel lens. It gets slightly better when there´s some water between the bag and the plate (that seems to take care of itself). You have to be really careful to avoid soaking the tinder.

I tinkered with the plastic bag/water lens for about an hour once. Never even bothered with tinder, since it was pretty clear I wasn't getting a very good focus. I didn't think of pinning it to a sheet of clear plastic, that may have helped. I can also see this might be a little easier in southern latitudes around noon; my so-called "lens" sagged down because it had to be at an angle at my northern latitude, throwing the shape way off.

In Jules Verne 1874 novel, "The Magnificent Island", balloon-wrecked survivors start a fire by taking the glass faces off two watches and filling the space between them with water.

The whole novel is online here and other places, with the relevent bit in chapter 10, and chapter 9 is also interesting for their failed attempts. Indeed, the rest of the book is good too; I loved it as a child.

I agree... as small, light and thin as they are it's pretty hard to come up with an excuse not to carry one although I admit that I myself do not currently carry one though I have in the past and may again in the future.

Looked at the website posted cheap prices but the shipping costs more than the lenses.
Lee

Try bookshops.

Sue

I went to a Grand & Toy (big chain of stationery supply stores) here in Calgary and asked about the credit card sized fresnel lens. They didn't have any in stock but they ordered a couple in for me - $0.99 each (Canadian). (I ordered two because I felt guilty about making a special order for less than a dollar.) <img src="/images/graemlins/blush.gif" alt="" />

Many bookstores will sell a fresnel lens bookmark which will work at least as well, but may cost a bit more. (Otoh, you may be able to cut it in two and get two lenses out of it.)