Hello!

 

I am trying to start fire from the sun using a lens (from ice, water in a plastic bag and glasses) in Norway. I haven't had success.

 

The midwinter sun is much lower here as you can imagine. I am interested to know if the 'weaker' mid winter sun is less likely to begin a fire? and if there are physical ways around this. can I simply leave the tinder in the focus point for longer, or will it simply not get hot enough?

 

Many thanks.

The Sun's rays at the Earth's surface in high northern latitudes in the winter is "weaker" because it travels through more atmosphere due to its lower angle to the horizon, so it'll take more time or you'll need a larger lens to focus more rays on the object.

 

Important! Keep in mind that you want to focus the "heat" (infrared) from the sun and not the sun "light" (visible spectrum). The diagram below shows that IR has a longer focal length than visible light. Because we can't see the heat rays, it's hard to tell if they are focused optimally on the object. All I can recommend for now is that you focus the sunlight, and then back off the lens a bit.

 

Ewmon,

 

Beautifully explained, and a useful IR tip.

 

 

Thanks very much.

 

 

 

 

Cotton wool should be a good candidate provided it absorbs IR well. Its filaments' heat inertia is tiny, and the autoignition temperature is low. Protect well from wind. Possibly better than tinder. I used cotton wool as a child (a long long time ago!) to make fire when my mom hid the matches for incomprehensible reasons.

Edited November 3, 201213 yr by Enthalpy

Another great tinder is tumble-dryer fluff

I am going to try tumble dryer fluff!

The thin silvery outer skin of the Silver Birch tree is very flammable if you have them around...just peel some slivers off.

Edited November 27, 201213 yr by StringJunky

Thanks StringJunky, Natural tinder is a wonderful thing! King alfred cakes have to be my favorite. http://www.mushroomdiary.co.uk/2010/06/cramp-balls/ they have a good glow.

The thin silvery outer skin of the Silver Birch tree is very flammable if you have them around...just peel some slivers off.

Thanks StringJunky, Natural tinder is a wonderful thing! King alfred cakes have to be my favorite. http://www.mushroomdiary.co.uk/2010/06/cramp-balls/ they have a good glow.

 

I shall watch out for them. I go night fishing and a friend and I were plagued by mosquitos one night and we found that smouldering pine cones waved around oneself kept them off...at least while they were burning anyway!