A lens that changes shape

The idea

The eye contains a convex lens that can change its shape, which allows us to see both nearby objects and things far away.

Book, then tree

You read a book. Then you look up at a tree far away. In a moment, both look sharp.

What do you think lets your eye do this?

• A lens inside the eye changes its shape
• The eye moves closer to the tree
• The book and the tree change their size

Focus the eye

Look at the book, then at the tree. Make the eye's lens thinner or thicker until the picture is sharp.

An amazing lens

The eye contains a convex lens that can change its shape. This allows us to see both nearby objects and things far away.

Lenses are used everywhere: eyeglasses, cameras, telescopes and microscopes all use lenses.

• Looking at | The eye's lens
• A book nearby | Thicker
• A tree far away | Thinner

Notes

The eye contains a convex lens that can change its shape, so we can see both nearby objects and things far away.

Check yourself

What kind of lens is there in our eye?

What lets us see both a book and a tree far away clearly?

Which of these use lenses?

• A concave lens. The eye's lens is a convex lens.
• A convex lens — correct. Yes. It is thicker at the middle.
• A plane mirror. Light passes through the eye's lens to the back of the eye. It is a lens, not a mirror.
• The lens changes from convex to concave. It stays a convex lens. Only its shape, how thick it is, changes.
• The eye's lens changes its shape — correct. Yes. It becomes thicker or thinner.
• We walk closer to everything we look at. We see a far tree clearly without walking to it. The lens changes shape.
• Eyeglasses, cameras and microscopes — correct. Yes. All of them use lenses.
• Torch reflectors. A torch reflector is a concave mirror, not a lens.
• Side-view mirrors of vehicles. These are convex mirrors, not lenses.