Make a Camera Obscura From a Cereal Box — or Practically Anything Else

The camera obscura can be mesmerizing, projecting a live image of the word in miniature. In this Instructable, they serve as an engaging introduction to how lenses work, as well as helping to explain the workings of cameras and our eyes. Artists have used camera obscura as an aid to drawing, and have made camera obscura out of hotel rooms, tents, cars, and matchboxes. You can make a camera obscura with (or without) almost any materials, so it lends itself to a remote learning project.

There are many Instructables with designs for camera obscura that range from simple to complex. These instructions use a cereal box, although I also give other examples. You will need a lens — a simple school magnifier is used here (and if you really do not have a lens, there are ways around that too).

The point is, once you understand the basic optical idea, it is fun to build camera obscura out of everything and anything!

• Magnifying glass (plastic school magnifiers are fine)
• Small recycle box (the example uses a cereal box)
• Translucent plastic from a plastic lid, milk carton, or the bag from inside a cereal box
• A sheet of white paper
• Tape
• Scissors
• Optional: Additional lenses to experiment with, aluminum foil, paint, toilet paper tubes and other craft and recycle materials to create alternative designs

Have students experiment with using their lens, a sheet of paper, and an overhead light, flashlight or lamp.

Be safe: NEVER use the sun in these experiments, this can start a fire or injure your eyes. Also, do not look through the magnifier at lights -- rather shine the flashlight or lamp through the lens onto the paper or other surfaces.

A magnifying glass bends the rays of light as they pass through it, causing the light rays to converge and cross over. By experimenting with the distance between the light, lens, and the paper, you can find the distances at which you can project focused images of the light source onto the paper. (Search for camera obscura on the web for diagrams showing the path of light.)

If you have access to different lenses, experiment with how they work:

• What happens with bigger lenses?
• Stronger magnifiers?
• Differently shaped lenses?

After students have had a chance to get to know their lens, have them find the distance between their lens and the paper that forms an in-focus image on the paper. It is easiest to work underneath an overhead light, but you can also set up a flashlight or lamp several feet away as a light source and work horizontally. Have students measure and record the distance between the lens and the paper when the image of the light source is in focus.

Note: If you do not have a lens, you can use a pinhole — essentially making a pinhole camera minus the film. Use a pushpin to poke a hole in a 3” square of aluminum foil. The foil will help make a clean hole. You can use the pinhole in the same way as the lens, but the image will not be very bright (the pinhole lets in less light than a larger lens). For this activity, a lens produces a more satisfying result.

Now that we know how to project an image on paper we are halfway there. Putting the paper inside a dark box keeps our image from being overwhelmed by other light in the room.

Find a box that is the right size: one dimension of the box (ie front to back or side to side) should be approximately the same length you measured between your lens and the paper when the image was in focus.

Cut a hole in the front of the box (or one side if you are using that dimension) that is just a bit smaller than your lens/magnifying glass. Tape the magnifying glass over the hole.

If you use a thin-walled box — like a cereal box — you can squeeze the box a bit as you use it, changing the distance from front to back, and focusing your image! Can students think of other ways of focusing?

You have two options for a screen:

You can tape or glue a piece of white paper on the inside surface of the back of the box to serve as a screen. To see the screen you will need to keep one side of the box open, or cut a hole.

Alternatively, you can make a “rear projection screen”. Look at the size of the image projected in the box, and cut a hole in the back of the box a little bigger than the image. Tape a square of translucent material over the hole.

In the example, the screen is about 5” across. A screen made from a translucent plastic lid or translucent plastic milk carton works well; so does a square of the translucent plastic bag inside many cereal boxes. You can also experiment with tracing paper, plastic lids, wax paper, or other materials.

Experiment!

• Try pointing the camera obscura out the window. (Be safe: Never point at the sun!)
• Try looking from a bright room into a dark room, or vice versa.
• Try putting things in front of the lens, or blocking part of the lens.
• Can you improve the design -- for example painting the inside of the box a dark color may help reduce stray light.
• Try out different materials and new designs. You can make a fun camera obscura with a toilet paper tube — cut it to the length that brings your image into focus. What happens if you change the shape of the screen?

A camera obscura is a good model of the workings of a camera. Instead of the screen, a camera has a sheet of film. (Look up Instructables for making a pinhole camera if you want to try it.)

A camera obscura is also a good model of how your eye works. Instead of the screen, your eye has a retina — a layer of light-sensitive cells that transmit the image to your brain. Your eye also has a flexible lens that is pulled by muscles — the lens changes shape to focus! If you want to make your camera obscura even more like an eye, you can add an iris to change how much light gets through — the iris opens in low light, and contracts to a small opening in bright sunlight (see resources).

Wikipedia, and many other sites, offer information on the long history of the camera obscura, and diagrams of how they work and the path of light.

Search Instructables for a great variety of Camera Obscura and Pin Hole Camera ideas. Also see:

https://www.exploratorium.edu/video/camera-obscura...

https://www.exploratorium.edu/snacks/personal-pinh...

Instructables also has many options for making an Iris out of cardstock or other materials, for example; https://www.instructables.com/Mechanical-Iris-Car...

Abelardo Morell is an artist who makes and uses camera obscura to produce amazing images. You can find others by searching the web for "camera obscura photographers".

This work is made possible by support from STAR, a Biogen Foundation Initiative. The team at Lesley supporting this initiative includes faculty and staff in the Lesley STEAM Learning Lab, Science in Education, the Center for Mathematics Achievement, and other related Lesley University departments and programs.