Physics Lesson for Survivor (tm)

I was reading some commentary about the latest installment of Survivor. For those who may have missed the show, the castaways were not given any means to make a fire, and since their water is contaminated they really need to get some fire going pronto.

After three days or so, the castaways have all failed to produce any flames at all, and the situation is looking grim. Some armchair survivor-geniuses have wondered why they don't use the eyeglasses that some tribe members are wearing to start a fire? After all, that's what they did in the Lord of the Flies, right?

Well, William Golding may have been a fine author, but he didn't know crap about physics.

Near-sighted (myopic) people wear lenses that are concave. While concave mirrors focus light, concave lenses diffuse light. If you stick a pair of glasses worn by a near-sighted person over a piece of paper or other clear surface, you will notice a penumbric shadow where the lenses are. This is not a shadow! It's the light being directed away by the lenses in the glasses.

Far-sighted people wear lenses that are convex and that focus light. Sadly, there isn't much reading material when stranded in Panama, so it is unlikely that any far-sighted tribe members brought their glasses. Of course, even if they did, you would need to have someone who was very seriously far-sighted to get a pair of glasses that actually focused the light in any reasonable way.

Sadly, that means that our castaways are unlikely to produce that much fire in the near future through optics alone... they'll have to make it themselves or... more likely, have it given to them by Mark Burnett when he realizes that his precious contestants are going to die.