Applications of Light & Lenses
Camera obscura and pinhole camera
Leon is in the basement getting his camping gear. It’s always so dark in here, even during the day. It’s a bit spooky… Oh no, Leon's torch has gone out! When his eyes adjust to the darkness, suddenly he sees a moving silhouette on the wall. Aaa!
What is that? A ghost? I’m dead. One second, Leon! Take a closer look… Wait, it’s Lina in the garden just outside!
It looks like a film playing on the wall… But she’s upside down! Hmm. What is happening here? When Leon’s torch is off, the only source of light is a tiny opening to the garden. Light rays from outside come through this opening.
When the rays hit the white wall on the other side of the basement, they form an image. Remember Lina is standing in the garden. Light rays outside, reflected from Lina’s head, travel in a straight line, through the opening, and hit the basement wall at what is the bottom of the image Leon can see. The rays reflected from her feet travel in a straight line and are projected onto the wall closer to the ceiling, at the top of the image. The image is inverted.
This optical phenomenon is known as camera obscura or a pinhole image. And you don’t have to be in a dark basement to see a pinhole image. You can observe this phenomenon using a device called a pinhole camera. And you can make this device yourself! How?
To make a pinhole camera, you will need: - two sheets of thick black card, - some thinner black paper or aluminium foil, - sticky tape, - a pin or a needle, - and some thin semi-transparent paper, such as baking paper or tracing paper. Start with making the body of your pinhole camera. Take one sheet of card and roll it to form a cylinder. Tape along the edge. Then, place the thin black paper or aluminium foil tightly against one end of the tube, creating a flat surface.
Secure it with tape. Using the needle, make a tiny hole in the centre of this flat surface. This is where the light will come through — the aperture. Take the other sheet of card, and roll it into a cylinder just a tiny bit smaller than the first tube. Secure with tape.
This tube should fit very tightly inside the first one. Place the semi-transparent paper tight against one end of the smaller cylinder and secure with tape. This will be the screen you’ll be able to see the image on. Now, slide the smaller tube, covered end first, about half way into the bigger tube. Your pinhole camera is ready!
Point the end with the pinhole at a bright object, and look through the open end of the smaller tube. You should be able to see an inverted image of the object you’re looking at on the screen inside! You might need to cover the spaces between your eye and the tube with your hands, to make sure that the only light coming in enters through the aperture. If the image is blurry, you can try to focus it, either by sliding the smaller tube further inside the bigger one, or by moving closer or further away from the object. I wonder what would happen if I make more pinholes… Or if I use a shoe box for the camera body… Well, why don’t you carry on and experiment yourself?