Saturday Science: Camera Obscura
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. 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!
- Cereal Box (make sure you eat all the cereal first!)
- The bag that came inside the cereal box
- Pen or marker
- Duct tape or electrical tape
- A pushpin or thumbtack
- Take the wax paper bag out of the cereal box and make sure all the cereal dust is cleaned out. Flatten it out on a table and set the bottom of the cereal box down on top of it. Using your pen or marker, trace a rectangle on the bag that is a couple of inches bigger than the bottom of the cereal box. Then take your scissors and cut the rectangle out.Using your scissors again, 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’re finished, the cereal box should be in two pieces: the
- Using your scissors again, 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’re finished, the cereal box should be in two pieces: the bottom, and the rest of it, that is now open at both ends.
- Using your tape, attach the wax paper rectangle to the cut-off end of the top half of the cereal box. Fold the extra over the sides of the box and tape it down as securely as you can. Make sure the paper is as smooth and flat as possible by pulling all four sides nice and tight before you tape them down.
- Tape the bottom of the cereal box back into position, so that the paper you just attached is sandwiched between the two pieces. You’ll want to use duct tape or electrical tape because they are opaque, which means light can’t get through them and into your camera obscura.
- Using your pushpin, poke a hole right in the very center of the bottom of the cereal box. This will let the light in so that it can hit the rectangle and project an image.
- Look through the top of the box and point your camera obscura at all sorts of things. The lighter they are, the better it will work!
Did you notice anything weird when you were looking through your camera obscura? Like, maybe, that everything you look at looks upside-down? It’s pretty strange!
This is 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 wax 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 wax 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. 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.