empty Pringles® chip can
marker
ruler
X-Acto knife or utility knife (ask a grown-up to help you cut)
thumbtack or pushpin
masking tape
aluminum foil
scissors (if you want)
bright sunny day, or a burning candle on a cloudy day

Take the plastic lid off the Pringles® can and wipe out the inside. (Save the lid!)

Marking the can Draw a line with the marker all the way around the can, about 2 inches up from the bottom. Have a grown-up cut along that line so the tube is in two pieces.

The shorter bottom piece has a metal end. With the thumbtack, make a hole in the center of the metal.

Put the plastic lid onto the shorter piece. Put the longer piece back on top. Tape all the pieces together.

To keep light out of the tube, use a piece of aluminum foil that's about 1 foot long. Tape one end of the foil to the tube. Wrap the foil all the way around the tube twice, then tape the loose edge of the foil closed. If you have extra foil at the top, just tuck it neatly inside the tube.

Go outside on a sunny day. Close one eye and hold the tube up to your other eye. You want the inside of the tube to be as dark as possible-so cup your hands around the opening of the tube if you need to. Look around your yard through the tube. The lid makes a screen that shows you upside-down color pictures!

On a cloudy day, go indoors and view the flame of a lit candle.

Hold your hand below the tube and move it very slowly upward. Your hand is moving up, but you'll see its shadow move down the screen!

What's going on

How does a pinhole let you see the images carried by light? And why are these images upside-down and backward?

The simplest way to understand pinhole images is to take a look at what happens to light rays radiating from an object, such as a candle and it's flame, that vou are looking at with your pinhole viewer. Light radiates from all parts of the flame, and bounces off the candle body. A pinhole lets through only a portion of these light rays. Most of these rays are blocked bv the cardboard surrounding the pinhole. Only a few of the rays of light from the flame or candle are heading in just the right direction to shine through the pinhole of your viewer. Light rays from the top of the flame must slope down to pass through the pinhole. These rays hit the bottom of the screen. Rays of light from the base of the flame or candle itself must slope up to pass through the pinhole. These upward moving rays will hit the top of the screen. Think about this: if the rays from the top of the flame hit the bottom of the screen, and the rays from the bottom of the flame hit the top of the screen, then it seems like you should see an upside-down picture of the flame on your screen. (And you do!) The same logic applies to right and left so that the image is also reversed this way.

The flame has more points than the top and bottom. The same rules apply to light rays emanating from every part of the flame, and reflecting from every point on the body of the candle: only the light rays that are heading in just the right direction will pass through the pinhole. On the other side, these rays of light line up geometrically to make an upside-down and backward image of the flame and candle.

Your Eye Works Like This, Too!

Yes, yes, we know that the drawing for the eye is wrong, and that it is the lens of the eye, not the pupil, that serves the same function as the pinhole, but we didn't see the error until it was too late to find a nice drawing! We'll fix it next year!

Cereal Box Pinhole Viewer

Bob Miller, SF Exploratorium
with modifications by Tony Alfrey, Nixon Elementary Parent

You can make a simple pinhole viewer that lets you see the images carried by light shining through a pinhole. All you'll need is:

an empty cereal box or laundry detergent box that is at least 12 inches tall
waxed paper or tracing paper from an art supply store.
black tape or silver duct tape, the more opaque, the better.
an X-acto knife, a single-edged razor blade, or scissors
a pushpin or thumbtack

Making a pinhole viewer

If you're using a cereal box, remove the lining. Cut a big flap in the front of the box, cutting across the middle down one side, and across the bottom. I cut off the flaps from the top of the box at this point. You might find it useful to save these pieces for later use. It can be cut into strips and taped over the seams to help reduce light leaks.

Cut a piece of waxed paper that's as wide as the bottom of the box but a few inches longer. Tape it inside the box as shown, about two inches from the bottom of the box.

Use your pushpin or thumbtack to make a hole in the bottom of the box. Then close the flap and tape it back in place with black tape. Be sure to tape all around the flap so that no light can leak into the box except through the hole in the bottom. This step is very important, especially if the viewer is to be used outdoors. Also, use the tape to cover up corners of the box that may have light leaks.

Cut a slight curve along one edge where you removed the boxtop, so that the curve of the box more or less matches the curve of your forehead. You may also want to use the black tape to make a flexible flap along the edges where you removed the boxtop and the flaps. This will help block out light.

Using the pinhole viewer

We found that the pinhole viewer works well outside on a sunny day. It helps to stand in the shadow of a building, with the Sun behind you, so that the subject is in front of you and brightly lit. This helps reduce the light that may leak into your viewer. However, on a cloudy day, or indoors, a burning candle makes a good object to observe.

Look into the opening in the top of the box, squeeze the box so it fits tightly around your face, and use your hands to block light leaking in from around your face. You'll see an upside-down and backward image of the scene in front of you on the waxed paper screen inside the box.

If you make the hole bigger, the image will get brighter (but not bigger), and also more blurry. If you make more than one hole in the bottom of the box you'll get more than one image.

Credits

Material for this handout was shamelessly stolen, modified, disassembled, reassembled and edited for Noon Science at Nixon Elementary School by Tony Alfrey, and contains material from www.exploratorium.edu/science_explorer/pringles_pinhole.html, www.exploratorium.edu/light_walk/pinhole_todo.html and "The Usborne Big Book Of Experiments", Usborne Publishing, Ltd. Go out and buy the Usborne book; it has loads of fun stuff for kids to do, even if some of the explanations have errors. And, of course, what can we say about the Exploratorium, except to suggest that you become a member if you can!