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Here's one from Amazon for $8 that's A4-sized and probably weighs a few grams. Great for magnifying or building a solar oven. If you can find one a meter square

• dmix 7y ago
  > I had one of these for years and somehow lost it. I recently replaced it. One of the uses I put it to was starting fires. It will ignite a pine board in seconds. Don't get your hand at the focal point with the sun shining through it or you will burn the peewadden out of your hand. It's not as good as a magnifying glass for reading. I have taken pictures through one to blow a small picture up into a larger one. You’ve got to love Amazon reviews sometimes. Googling “peewadden” also has an interesting story from the American civil war.
• ljf 7y ago
  I used to run a site that showed people how use these to create a projection tv (a bad one!) from a fresnel lens and a CRT tv. Was a fun and simple project for kids.
  • PhasmaFelis 7y ago
    Anyone remember AcidWarp? It was a DOS program from the early '90s, distributed through BBSes, that generated lovely flowing color patterns. It came zipped with a text file with instructions for building a Fresnel-based projector for your PC monitor. Looks like it's still online: http://www.noah.org/acidwarp/ http://www.noah.org/acidwarp/