I carry three or four different means to set a fire in the backpack I carry when I go hiking; a credit-card sized fresnel lens is one of them. I also like to s

I carry three or four different means to set a fire in the backpack I carry when I go hiking; a credit-card sized fresnel lens is one of them. I also like to scavenge the huge fresnel lens from larger (40+ inch) rear-projection TVs - these are often thrown out by people during our "bulk-trash pickup" days. It only takes a few minutes of work to remove the front screen of the TV (they are designed to be removed). A few more minutes will net you a huge silver first-surface mirror, too. The fresnel lens from one of these TVs - mounted in a proper frame - can easily melt steel and rock. You have to be very careful when using it (wear proper clothing, plus welding goggles and gloves), and store it properly out of the sun afterward (because it can easily set things randomly on fire you don't want set on fire).