Make a camera obscura

February 1, 2022

The “Camera Obscura”, which literally means the “dark room”, was the world’s first camera. In this activity, we turn a room into a camera.

Parts

Black duct tape
A room with windows.
White chart paper.
Black chart paper.
A pin

Safety instructions

Once you get the room perfectly dark, it might be difficult to move around. Make sure unnecessary obstacles are removed from the room.

Steps

Tape up all the windows

Using as much of the black chart paper as you need, tape up all the windows in the room. Ensure that almost all the light is blocked off. This will take some time, but do it patiently and thoroughly.

Note: The above image shows the use of electrical tape, which can be used, however black duct tape is recommended. Electrical tapes will tend to expand and warp over time, unlike duct tape.

Make a pin hole

At a spot where the sun is shining on the window, make a hole with a pin - a 2mm hole is fine. Try to make the hole as a perfect circle.

Watch the magic!

Take the white chart paper and place it in the part of the light that’s coming in through the hole. Wait for your eyes to acclimatise to the low light conditions. And voila - you should see the an upside down image of the scene outside your window.

Make it sharper

Bring the white chart paper closer to the pin hole and you will notice the image becomes brighter, but smaller. Move it away, it will grow dimmer, but larger. Experiment to find the best position.

How does it work?

In a normal room, with light coming in from all directions, it falls on the objects in the room and reflects back in all directions. A portion of all of that light also enters our eye, and that’s why see the room and all the objects in it. But what happens when the room is completely dark? We see nothing, just pitch darkness, as you would expect.

Now, in this pitch black room we made a hole to let in just a few rays of light. This light, is now reflecting off an object outside the room and entering the pin hole and falling on the white paper we’re holding up. Light from each point that’s outside the room is directing a ray of light inwards…and ultimately re-creating the image on the paper.

Why is the image inverted?

A simple sketch will show why the image is turned upside down. Interestingly enough, our eye works just like a pin hole camera and also captures what we see upside down.

Camera obscura and the eye - same thing!

It’s the brain that then inverts the image so we see things the way they are in nature. It would be awfully hard to pick an apple from the tree, if the brain did not turn things right side up.

Why does the image grow brighter when moved closer

If you move the white chart paper closer to the pin hole, you will notice the image looks brighter and you can see the colors clearly. Moving it away from the pin hole has the reverse effect. Remember that the amount of light is the same in both cases; however, in the first case the light is spread over a smaller area thus appearing bright. In the latter case, the amount light covers a larger area and is “less dense”, thereby less bright.

Points to ponder

To focus, or not to focus?

Every camera lens a setting to adjust “focus” of the lens being used - when you have adjusted the focus correctly, the picture you take is crisp, and “in-focus” as one would say. But what about the pin hole camera? Can we adjust the focus? Or is the image always in focus?

What happens if you make another hole?

If you were to take the pin and make one more hole just next to the one that already exists, what would it do to the image? Would you see two similar images?