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It's possible to do it with ice that has been shaped into a convex lens. The ice needs to be clear and fairly large like 5 inches across. Obviously this won't work in the summer, and the cold temperatures won't help either, but it does look like it can be done.

See,

• How To Start A Fire Using Magnifying Glass Made Of Ice




• How Do You Start a Fire With Ice?




• Starting Fire With an Ice Lens




• Fire from Ice




• Build a Fire with a Slab of Ice

All of the above links are for starting a fire with a magnifying glass made from ice, would be interesting to see if there are other materials that can do this as well.

(Taking into account that we do have an "ice" answer already)

The one magnifying lens that is fast and easy to get and that does have an optical quality that actually helps vision as a magnifying glass are in fact drops of water. But that's for the "home-made field microscope" application of a magnifying glass.

If you consider starting fire by sunlight, you expect conditions where it may be easier to get directions during day via the sun rather than during the night via stars. I.e. either find south if you still have (local) time, or east-west from shadow if you don't have local time (slower - and precision depending on how much time you are willing to spend for this).

For starting a fire, depending on latitude and weather conditions, the quality of the lens may be far lower. And it may be an option to have a rough mirror: it may be far easier to collect sun from a much larger area by aluminum/rescue foil.

As has been mentioned in other answers, for vision, a pinhole device, similar to what is used for pinhole cameras, is your best bet. Short of water (which you have already ruled out), that's about the only natural option you have.

For fire though, you have multiple options:

• Don't discount making your own glass. Yes, it's hard, but you don't need high quality glass for a simple focusing lense for starting a fire, it just has to be reasonably clear.


• Ice has been mentioned already. This is pretty much your best option in really cold climates. Shaping a usable lens out of ice is not trivial, but it's not super difficult either.


• Mirrors are also an option. If you have some aluminum foil or, better yet, a mylar survival blanket, you can put together a convex reflector to focus the light. You could also just make a solar oven though if you only need the fire for cooking.


• This will probably sound utterly stupid, but you could make a lens out of sugar glass. Same general principals as for regular glass, just lower temperatures and therefore slightly easier.


• Don't discount other methods of creating a fire. Friction-based fire making is covered in survival training for a reason, it needs almost nothing and it works reliably (if you practice).

A clear mineral crystal can be worked to a lens shape with enough time and effort. Quartz, sapphire and ruby are likely candidates. Ruby lenses were common on wand style barcode reader pens.

Even some salt crystals are routinely used as lenses and optical windows in certain applications (lasers, IR and UV systems). Many of these salts and those you may crystallise or find will likely have a problem with moisture.

If you can recover a source of glass, you should be able to melt it using a charcoal fire with bellows to force air and increase the temperature. You'd need a mould, for which clay would be good. This can be worked into shape, smoothed, and dried before casting the glass.

This requires real glass, not plastic as is commonly used in spectacles , and not laminated (many car windows). Thermoplastics have a lower melting point but would be very easy to burn.

The resulting lens should be able to start a fire, but getting anything like the right form or surface quality for use as a magnifier or corrective lens is probably too much - for that you'd need to polish it (though jeweller's rouge is made from finely ground rust, so it's not completely impossible to improvise a polish).

Though, this probably won't help making a fire, but ...

As I'm short sighted by myself, I'm using this simple technique to focus my eyesight, if I'm out of my glasses. It works pretty good at night, but you need to have a general clue where to look before you apply it.

The one I use, is creating a kind of resizable diamond by putting thumb and index fingers together, then connect both hands (kind of 3mm-by-3mm square hole)

The one used in video, is a small hole created by one single finger closed to the palm itself.

And, in fact, any small hole would help, but the fingers are readily available and, more than that, are adjustable.

Similar to demigod's answer: grab a chunk of cardboard, or a sheet of bark, and punch two small holes spaced at the separation between your pupils. Wear this as though they were goggles. Due to the magic of optics :-) , you won't have a great field of view but what you can see will be in near-perfect focus.

As to firestarting, forget about using solar heating unless you can find a big chunk of obsidian and a near-spherical rock to grind a concave mirror. Use direct friction techniques to start your fire. See for example, this bow & peg tool.

It's also possible to start a fire using a plastic bag filled with water.

If by any chance you stumble open some waste of people that left it behind, or you happen te have kept that one sandwich bag of yours, you could use the lens-like properties and start a fire.