Despite its generally good functionality, a small magnifying glass is recommended to be used in a survival kit only as a backup or backup source for producing fire.
Magnifying glass or Fresnel lens in a survival kit, their use for producing fire during survival in emergency or extreme situations.
The main and irreparable disadvantage of magnifying glass is that they can only get fire in the presence of direct sunlight. But if you still decided to put a magnifying glass in your wearable survival kit, then you should give preference not to ordinary small glass magnifying glasses, but to a Fresnel lens in a plastic version and the size of a bank card.
A Fresnel lens is a flat lens containing a series of closely spaced grooves. They provide refraction and concentration of light flux in a narrow angle of dispersion. Proposed in 1823 by the French physicist, one of the founders of the wave theory of light, Augustin Fresnel, the lens design provides it with a small thickness and lower weight compared to classical.
Fire production with a magnifying glass and a Fresnel lens.
The stronger the direct sunlight, the better and faster the results. But in winter it will be much more difficult to create with a magnifying glass or a Fresnel lens enough heat to reach the ignition temperature. It’s worth starting fire production by placing the lens at a slight angle in direct sunlight and a few centimeters from the prepared tinder. The light amplified through the lens forms a semicircle on the tinder. Rotating the lens slightly makes it possible for the semicircle to turn into a circle. Then carefully move the lens up and down until the circle becomes as small as possible.
If everything is done correctly, then this place of concentrated sunlight will begin to smoke in two to three seconds. Then after some time a fire will appear. In addition to concentrating solar radiation, and thus producing fire, a magnifying glass or a Fresnel lens will help to make out details on topographic maps, to remove a splinter from a finger or a mote from the eye.
Extraction of fire with a transparent plastic bag and condom.
As an alternative to a classic magnifying glass or a Fresnel lens, you can consider a transparent plastic bag or condom. By collecting water or your own urine into it and thus getting a makeshift lens, you can likewise make fire on a sunny day. True, with a pack or condom it’s a little harder and longer to do than with a lens.