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fresnel lenses, bigger is better

Randall

Richard Proenneke
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Ahh, I gave up on magnifying glasses and credit card sized fresnel lenses; I got nothing with the tiniest focus point held steady for 15mins or more :oops:. Your explanation of size explains everything.
 

Wave Man

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forget the credit sized lenses mate and buy an A4 lens, they are about $5 on eBay. They make solar easy and you'll find you are setting everything on fire with one. The C/C lens is only for emergency use, not for regular use.

I do like a 50mm glass lens as well, but they don't compare to my A4 lens.

I can get fatwood alight with my A4 lens in about 10 seconds, grass is easy as is paper or paperbark.
 

Wave Man

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I don't deal with aliexpress, you are welcome to and more power to you but eBay already does them for around $5 (for the A4 sized lens) which is IMHO is already a bloody good price.

I have found though once you try to go bigger than A4 the price drastically increases. A 30cmx30cm lens is around $50.

Big lenses are dangerous and are capable of melting metal and glass.
 

Wave Man

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more explanation on this, the bigger the lens the more photons the lens can collect and concentrate and thus generate more heat. Magnification has little to do with it. So the larger you go the better.

Ignore magnification (2x or 3x is all you need) just find the largest-sized lens you can comfortably carry.

These A4 lenses fit in a haversack very well (I know I have one fitted in my bushcraft haversack)

The A4 lenses I am using are 3x and aren't very high magnification (they are the same magnification as the C/C fresnel lens)

A4 lens results (all set alight)
all types of char, as soon as you focus the focal point instantly embers
non-charred punk wood 5 seconds to char and ember
fatwood curls 5-10 seconds
grass 5 seconds
palm fronds 10 seconds
pine needles 10 seconds
crumpled up paper 5 seconds
paperbark 30 seconds (one type went up no problems another type struggled, I could get it alight but had to keep going at it to keep it alight)
birchbark 15 seconds
cattail fluff failed
cotton wool rounds failed
amadou and chaga as soon as you focus the focal point
my dried egg carton biscuits, 20-30 seconds to develop an ember, some times you did have to do again to reestablish the ember.
**as soon as you get a focal point you should see smoke
 
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