Cameras are everywhere these days. In phones, computers, tablets, and sometimes even all alone by themselves. In the modern age most cameras are digital, which means they store pictures using electronic memory like computers. In the not-too-distant past, cameras used materials that were photosensitive, which means that they change when light is shined on them. Light from the outside world would shine on the photosensitive materials and leave an image on it.

Back before anyone invented photosensitive materials, though, people were still experimenting with ways of capturing an image of the world with a box they could look through. The camera obscura (Latin for “dark chamber”) is one of the ways they did this, and humans have been building camera obscuras for thousands of years, since ancient Greece.  Some are so big you can sit inside! (This one is in New York).

Today you’re going to follow in that grand tradition and build your own camera obscura that will allow you to see the world in a very different way!

You’ll need:
A piece of deli paper
A toothpick
Black electrical tape
A push pin
Painters tape or other tape
An empty cereal box or other, similarly shaped box
A pencil or pen
Good scissors

(1) Using your scissors, cut all the way around the cereal box a few inches above the bottom. You want your cut to be as straight as possible. When you are finished, the cereal box should be in two pieces: the short bottom section and the rest of the box.

(2) Trace the box bottom on the piece of deli paper and carefully cut out the tracing.

(3) Using your tape, attach the paper rectangle to the box bottom. Fold any extra paper over the sides of the box and tape it down. Make sure the paper is as smooth and flat as possible by pulling all four sides nice and tight as you tape them down.

(4) Using the electrical tape, tape the bottom of the cereal box back into position, so that the paper you just attached is sandwiched between the two pieces.  Electrical tape is opaque, which means light can’t get through it and into your camera obscura.

(5) Cut an eye hole out of one of the top flaps on the box.  Then use the electrical tape to tape the top closed.
NOTE: We recommend putting your eye hole in the middle – where the “ee” in the Cheerios box is located, not over to one side like we’ve done in this box.

(6) Tape all the seams on the bottom of the box so light can’t get through them.  Then use your pin to poke a hole right in the center of the bottom of the box.  If you look close, you can see the head of a pin in the middle of one of the “e’s” in the picture below.

(7) Use your toothpick to make the hole a bit bigger.  This hole lets the light into the box.  The light will shine on the rectangle of paper and will project an image of whatever the box is aimed at.

(8) Go outside. Point the bottom of the box at something well lit by sunshine.  Look through the eye hole on the top of the box.

HINTS:
You may need to use one hand to shade your eyes from the sunshine.
You will need to give your eyes a few moments to adjust to the dim light inside the box.
Things with a lot of contrast work best – like a tree with the sky behind it.

What do you see on the paper inside the box?  What’s weird about what you see?  Why do you think that is happening?

What to know more?  Read on!

Did you notice anything weird when you were looking through your camera obscura? Maybe you noticed that everything you look at looks upside-down? It’s pretty strange!

This happens because of the way the light moves through the pinhole. You’re looking at objects that are way bigger than the pinhole. The light coming off of them only travels in straight lines, so when the light from the top of the object goes through the pinhole, it’s moving down towards it. It keeps going down and ends up on the bottom of your paper screen. The opposite is true of the light from the bottom of the object: it moves up to the pinhole and ends up on the top of your paper! Think of it like spraying a garden hose through a little hole in the fence. If you spray from above the hole, the water will shoot down out the other side, and if you spray from under the hole it will shoot up when it comes out.

Your eye actually works the same way. The light gets flipped going through your eyes, since they’re small holes, too, and when it hits the back of your eye and starts to travel to your brain the whole world is upside-down! Luckily, your brain knows better and flips it back right-side up for you.

Experiment with the size of the pinhole. You can wiggle the toothpick around in the hole to make it bigger or use something else to make the hole bigger. Bigger holes will let more light through so you can see dimmer objects, but they will make it harder to focus and get a good view of what you’re looking at.  If you decide your hole is too big, you can always cover it with a small piece of electrical tape and make a new hole.

We got this activity from The Children’s Museum of Indianapolis.  If you liked it, check out their other activities!