Follow these instructions to make your own pinhole camera and learn about how physicists use them.
You don't need an expensive camera to take photographs. Try making your own pinhole camera out of a few simple items from around the house. Pinhole cameras allow light through a tiny hole, making pictures with a soft, blurred, dreamy effect (with practice, you may be able to take sharply focused photos).
Pinhole cameras usually consist of a sealed box with a pinhole on one side and some film or photographic paper on the other side to record the image. Here we'll make a pinhole camera that doesn't use film, so you'll see the image but not record it. Using greaseproof paper instead of film you can test the theory of pinhole projection for yourself and view the world upside down.
What you need
To do this activity you will need the following items:
What to do
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Paint the insides of both boxes black.
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When they're dry, cut a small square in the centre of one side of the first box. Using a pin, make a small hole in the aluminium foil. Tape the foil on the side of the box so the pinhole is in the centre of the square you cut out. Cut off the opposite end of the box and stick a piece of greaseproof paper over it, making sure it's stuck tightly without any creases.
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Cut out another small square in one end of the second box, just big enough to look through. Next, cut off the opposite end of the second box. Use tape to attach the open end of the second box to the greaseproof paper end of the first box. Look through the viewing hole at the greaseproof paper. Use tape to cover any holes that allow light to leak through into the box from anywhere other than the pinhole and viewing hole.
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Take your pinhole 'camera' outside and look through the viewing hole. You should be able to see the world upside down on the greaseproof paper. If you can't see anything, try making the hole a bit bigger until you get an image on the paper. Experiment with different sized holes to find out which size gives the best effect. The hole is called the aperture: the bigger the aperture, the brighter the image. But as it gets bigger, the picture gets more out of focus.
What's happening
Here's how a pinhole projects an image. Light travels in a straight line unless it's diverted, so light travelling from the base of an object will travel in a straight line through the hole and hit the top of the surface opposite the hole. This is why the image appears upside down.
Leaves on a tree created a natural pinhole projection image of a solar eclipse!
Photo: Justin McGuire, CSIRO. Pinhole effects were discovered long ago when people noticed images of the sun beneath trees. Overlapping leaves can form pinholes through which light passes to form a circular image of the Sun on the ground. Physicists today use multiple pinhole optics to take photos of high-energy X-rays and gamma rays from black holes and exploding stars.
It can be expensive and tricky to process film or use photographic paper, but with an adult's help you might like to try converting your pinhole viewer into a camera.
Be careful, as the film or photographic paper must not be exposed to the light - load the camera in a dark room.
Caitlin White
For more hands-on activities, join CSIRO's Double Helix Science Club.
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