What are the advantages of a Fresnel over a small magnifying glass (out of a microscope) in a small PSK?

A Fresnel lens will have a larger light-collecting area for the same weight. That's important if you are trying to start a fire with it.

I have never had very good success with a fresnel lens. I live in Arizona and you would think the sun would start about anything, but not so.
Anyone else had problems starting a fire with a fresnel lens??

In the UK I've never had any success with either fresnel lens or proper magnifying glass. It must be possible, but you probably need a lens bigger than a credit-card at this latitude.

When I tried the "polish the bottom of a soda can" thing, I had lousy results until I smeared some charcoal onto a piece of white cotton (gun cleaning pad, actually). I think the main thing the charcoal did was to increase the amount of light absorbed by the cotton. I got a "coal" this way I was able to start a fire with. Wrapped the smouldering pad in a handful of dried grass and blew. Worked better than I ever expected. <img src="/images/graemlins/smile.gif" alt="" />

So. I'm thinking it's all about the tinder. Maybe try the standard cotton ball / vaseline but with something on the cotton to darken it up enough to catch. I'd imagine the fresnel lens would work at least as well as (and probably better than) the bottom of a coke can.

I live in the 37 latitude and when I was a kid I couldnt burn things in winter when overcast with my favourite lense which was almost an inch across. I havent had a fresnel lense to try and see how that goes.

As a kid in northern Alberta, at latitude 58'24" (way up North) I could easily start fires with a magnifying glass in the summer. We darned burned down a couple of houses doing it. It's not hard to do, on a bright sunny day, with a little patience. As I remember it(45 years ago), you had to use dark colored tinder to make it work best.

Hi Biggzie, that's got to be 37 degrees south. In my post to this subject I also neglected to mention north or south for latitude. I guess given the global nature of this forum we should be more precise. When I was reading your post, I was trying to figure out in my mind where in the US you were, until I read your name and location beside your post. As a Canuck, I always assume anything south of 49 degrees is US. How's the weather way down there?

Being the angle from the equator I didnt think it would matter that much, apart for you guys being upside down <img src="/images/graemlins/smile.gif" alt="" />
If you click here mirror.bom.gov.au/products/IDR143.shtml you can see for yourself <img src="/images/graemlins/smile.gif" alt="" /> The inner circle on the map is basically my stomping ground. Its a nice 18 degree C semi overcast day out, which makes a change from yesterday where my place took the brunt of a storm cell at 5am and full cloud cover most of the day. I now have a roof to fix over the weekend. I wouldn't have a prob with a lense between clouds today.

One thing I will say about the local weather is that when I was a kid, in winter we would get 2 to 3 weeks of overcast constant drizzle to full rain. Now all that weather seems to pass below the bottom of Aust out to sea. So global warming is going full steam ahead.

I'll trade you an Aussie radar map for a Canuck one. http://www.weatheroffice.ec.gc.ca/radar/index_e.html

I'm just above the "a" in Vancouver on the west coast. Rain today and the 7 day outlook is for rain every day. They don't call this the wet coast for nothing.

Im about 15 km SW from the crosshairs on the map.
I assume by the term Canuck, you mean Canadian?

This place is the wettest part of the state, But this is the dryest state in Aust. We are the first point to slow the bad weather down before it hits Melboune. The weather comes streaming accross the Bight from the bottom of Western Australia then hits us. There is a standing joke with the locals about knowing you are getting close to Mount Gambier by the clouds overhead. Thats quite a contrast considering that we have a desert 400km North of here, but looking locally you wouldn't know it apart for 3 months over summer.

fordwillman,

I have had the same result. I live in Phoenix. I tried 3.5" glass magnifying glass. I can get wood to smoke a little but that is all. It is also very hard on your eyes. I have decided that even if it could start a fire I would not use it because it could damage my eyes. I want to keep what vision I have left.