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Gallery 2

Fresnel Lens

Lenses that magnify images can come in different shapes and sizes.

How it works

Look at a friend's face through the Fresnel lens and see your friend's nose magnified many times!

Things to try or ask around the exhibit

  • 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?

Background

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!

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.

Finding the science in your world

Fresnel lenses can be found on the back windows of cars, in lighthouses, on traffic lights and overhead projectors and inside some car tail lights. They are often used in outdoor settings because they can be made from plastic (making them lightweight and cheap) and they tend to be thinner and more durable than other types of lenses that would be needed to create the same level of magnification.

Many hand-held plastic magnifying sheets that are used to enlarge text for people with vision impairments are also Fresnel lenses.