Pinholes and Optics
Pinholes are a great way to observe a solar eclipse… but frankly they’re super cool in their own right.
Here’s three different pinhole viewers; make them and play with them and you’ll have a pretty good idea about how pinholes function like lenses.
Pinhole Projector 1
Gather: Lamp with metal shade (like a desk lamp) Foil Pin Clear bulb
Insert the bulb and cover the opening of the shade with foil. Point the light at a blank wall and poke holes in the foil.
What do you notice? Is the image shaped more like the pinhole or more like something else? Let the lamp cool and study the bulb, what do you see?
Pinhole Projector 2
Gather: Small cardboard tube Wax paper Black or dark construction paper Foil Pin Rubber band
Cover one end of the tube with a square of waxed paper. Secure with a rubber band; try to keep this as smooth as possible. Roll the tube in a piece of black paper which is a few inches wider than the tube, aligning the open end of the tube with the edge of the paper. Locate the end of the tube that is farthest from the wax paper and cover it with foil; secure with a rubber band if needed. Poke a hole in the foil with a pin. Point the foil end of the tube at a bright sky and look through the other end at the waxed paper screen. NEVER POINT THIS AT THE SUN!! Look for clouds or trees against a bright sky.
Notice: What do you notice? How does the image look like the scene you’re seeing? How does it differ?
Pinhole Projector 3
Gather: Cardboard White paper/cardboard Foil Pin Tape
Cut a small hole (2 or more inches square) in the cardboard. Cover this hole with foil using the tape. Poke a hole in the foil using the pin. Hold the projector outside so the sun shines on it and its shadow lands on a piece of white paper/cardboard. You should see a small, round, dot of light. As you move the cardboard farther from the white paper screen, you should notice that the round dot becomes larger and dimmer. Try changing the shape of the hole in the foil so that it’s still small but no longer round and repeat this.
Notice: What does the shape look like when you use a small pinhole? How does this change when you change the shape of the pinhole? This is the projector you will use during the eclipse. Can you think what you will see instead of a round image of the sun? If you’re looking for a more advanced version that makes a larger and relatively brighter image, check out this webpage posted by the Exploratorium.
Evaluate: In each case you should notice that the pinhole is projecting an image of the object behind it: 1) the filament, 2) the sky, 3) the sun. In each case, the image is upside down and reversed, but this fact is only noticeable with projector #2! Pinholes act a lot like lenses, though they tend to produce dimmer images—if you’re into pinhole cameras, you will know that it takes much longer to expose the film than with using conventional cameras.