What sort of camera lens would be best for starting a fire?
I just wondered if I was stranded somewhere and I wanted to start a fire using camera lenses, would it be best to use a telephoto or a wide angle lens, assuming they had the same aperture?
Dave - I think the biggest effect is essentially just the aperture of the lens and how big the lens is to start with. It's basically to do with how much light you can focus in onto that spot of the sun, so you want essentially something which will work in the dark as much as possible - so as low an F-stop as possible. A wide angle lens will work better and get more heat in that small space and cause ignition. But the amount of energy you can get in is limited by the radius of your lens so a big lens is better.
The biggest effect I would say is you want to use a cheap lens because the focal length of these lenses - designed to focus onto a sheet of film at the back of your camera - that's probably only 2 or 3 centimetres away from the back of the lens. And so, any fire you start is going to be very, very close to your lovely camera lens, so use as cheap a lens as possible.