Fresnel Lens

Magnify yourself or a friend using this flat lens! Light bends as it makes its way through the lens, making you (or just your nose) appear much larger.

Explanation

A normal magnifying glass bulges out in the middle. Its curved surface bends light so that things look bigger, much as a drop of water magnifies.

A Fresnel lens (pronounced “fruh-nell”) is a flat lens that magnifies. The small circular grooves on the surface are shaped like the curved sections of a normal magnifying glass. These sections bend the light in the same way as a normal lens—without needing as much material!

Fresnel lenses are used where cost and weight need to be kept low and great accuracy is not needed. The thinner lens allows more light through compared with a conventional lens.

Lighthouses, traffic lights, overhead projectors and some car tail lights use these lenses. Many hand-held plastic magnifying sheets are also Fresnel lenses.

Extras for Experts

Lenses can also be used to focus light.

Light travels at different speeds through different mediums (such as water, air, glass). Light can also speed up or slow down as it passes from one medium to another such as from air to glass lens.

As light hits the lens (particularly at an angle), some of the light continues to travel through the water or glass and bends (refracts), while some light bounces back and is reflected.

If the lens is shaped properly, then light beams hitting the glass at different places will be bent at exactly the right angle so that they all converge to a single point: the focal point.

It’s also possible to make small oven using the light from the sun and a lens!

Things to Try

Run your finger over the surface of the lenses to feel the grooves.
Poke your nose near the centre of the lens and get your friend to look at you from the other side.
Look at distant objects through the lens. These objects are beyond the focal length of the lens—what is different about them?

Questions to Ask

Have you seen plastic, grooved magnifying sheets before? Can you guess how they work?

Explore More

Frozen Shadows
Use phosphorescence in your favour—strike a pose in front of this special wall and a flash of light will cause your shadow to freeze behind you.

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