Lenses are used to focus light. Because focusing light is so important, you can find lenses in many places.
Perhaps the most common lens that we see are the ones in peoples
glasses. There is a small lens in each of our eyes. When that lens
isn't shaped quite right, light doesn't focus clearly and it's hard to
see things. Glasses put another lens in front of the eye to help focus
the light better for us. Then we can see clearly.
Another place to find a lens in in a CD player. A CD player works
by shining a laser (which is a type of light) onto a disc. The lens in
the CD player helps focus the laser onto the disc. Without that lens,
the CD player can't read anything.
Lenses are also used in telescopes. When we look up at the sky, we
see lots of stars. But we can use a telescope to look at a specific
star. The lenses in the telescope focus the light from a single star so
that the star we're looking at appears larger so it is easier to see.
(published on 10/22/2007)