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A lens is a clear (transparent) object (like glass, plastic or even a drop of water) that changes the way things look by bending the light that goes through it. They may make things appear larger, smaller, or upside-down. Some places lenses are used include spectacles (eyeglasses), contact lenses, cameras, projectors, microscopes, telescopes, magnifying glasses, etc. Each eye also has a lens.
They work by refraction, or the bending of light.
Lenses have three main shapes. Each different shape changes the image (making it bigger or smaller). The three types are:
The power of a lens is the reciprocal of its focal length: P = 1/focal length.