If you live in the US (or you know someone), and you have bulk-trash pickup (or can scavenge otherwise) - look around for an old 40 or 50 inch rear-projection t

If you live in the US (or you know someone), and you have bulk-trash pickup (or can scavenge otherwise) - look around for an old 40 or 50 inch rear-projection television. All of them use a large fresnel lens for the screen (they also have an interest lenticular lens as well - but that isn't as useful due to it's short focal length). This lens, properly mounted, is capable of melting glass, rock, steel, etc. IE - if you use one as a solar concentrator, know what you are doing, as they can be very dangerous (not a toy). There are plenty of instructables and such online detailing how to build and use one - for instance: http://www.instructables.com/id/Giant-Fresnel-Lens-Deathray-An-Experiment-in-Opti/ http://www.instructables.com/id/Giant-Fresnel-Lens-Deathray-...