Something has been troubling me for a while -- a lot of people advocate including a Fresnel or magnifying lens in their fire kit for starting fires. That's great, I wholeheartedly agree especially since the benefit-to-weight ratio is so high.

But so often I see vendors advertising higher magnification lenses and I see on Dave Canterbuy's videos and others advocate high magnification type lenses. I scratch my head and say "WHY?" the magnification has absolutely nothing to do with its ability to start a fire. You are simply taking the light gathering ability of the surface of your lens and concentrating it into a dot of high intensity light. Simply put, the larger the surface of the lens the greater then intensity of the dot of light when focused. A 2" dia. lens will gather 4x the light as a 1" dia. lens and concentrate 4x the energy making it easier to start a fire. A 4" lens will gather 16x the light into a point and so on. A really good quality lens with little spherical aberration is better because of its ability to generate a tighter focus point is worth the money but a higher magnification isn't. Similarly, a non-scratched lens will work better than one clouded with scratches.

The magnification affects the focal point not the ability to gather light. Am I missing something about simple physics here? Do these survival gurus know something I don't? Are you paying more for a high magnification lens that does nothing for you? Do we need snake-oil salesmen who trick you into spending more than you need to?