Photo credit: Gisle Noel; photo courtesy of Philip Greenspun; image source
Properties of a Liquid-Drop Variable Lens
Notice that both the ant and the small image of the flower are in focus in this photograph (high-res version)--therefore, both must be at approximately the same distance from the camera lens. Since a drop of water has a small radius of curvature, its focal length is short, only about half a centimeter, so the image is close to the drop and is much smaller than the flower itself.
-- For related activities and information, see Properties of a Liquid-Drop Variable Lens.
-- Build your own water drop lens at Kitchen Science Experiments: Drop Magnifier.
(This feature was updated on July 15, 2013.)
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Exploratorium: Snacks About Light
To do a simple experiment with a convex lens, go to Exploratorium: Snacks About Light, scroll down to the bottom of the list of activities, and click on "Water Sphere Lens." Try using a fishbowl of water as a lens. You can do the same activity with a magnifying glass, but be sure NOT to look through the magnifying glass into a bright light, or into the sun.
(This feature was updated on July 16, 2013.)