Why do you always hear about curved lenses? I have a magnifying lens that's flat. Explain that!
The surface of the lens is the most important part because that’s what bends light as it moves into and out of the lens. In 1820, Augustin Fresnel made this discovery and then created lenses that eliminated the glass in the middle, making a lens that was all surface. Today you can buy flat, plastic Fresnel magnifying lenses.
A drop of water makes a fine magnifying lens.   HERE’S WHAT YOU NEED
Clear plastic wrap
A newspaper
An eyedropper
1. Tear off a piece of plastic wrap and put it on top of a sheet of newspaper.
2. Using the dropper (or your finger if necessary), put different-sized drops of water in random spots on the plastic wrap.
3. Look at the words on the newspaper through the drops. Do the words appear bigger?
4. Look at the drops from the side. Notice that they’re curved out. You just made yourself a bunch of convex, or magnifying, lenses.

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This activity is from Exploratopia, © Exploratorium, published by Little, Brown, and Company