A camera obscura is the most basic form of analog photography and a great way to demonstrate how the eye works. Despite many decades of advances in technology, they can still be pretty magical.
Warning: this activity can be challenging. I have tried to design these instructions so that a 4th grader and older could do them alone, however, younger kids who have lots of experience making can probably handle it too. Young kids and anyone with fine motor challenges will need help. But it's worth it.
There are many types of cameras obscurae, but I will show two versions here. I will go into more detail with the first since it is more accessible, but if it feels easy, then try the second too.
For the first type, you need: tape (any kind will work), scissors, a pin, foil, a piece of translucent material (the inner liner of a cereal box, shown here, works really well; you could also use parchment, wax paper, or tracing paper), rubber bands (optional, but makes it easier to take apart), a toilet paper roll and a paper towel roll.
First, cut the toilet paper roll lengthwise, and reshape so that it will fit into the paper towel roll. Tape it so that it maintains its shape.
Then, wrap the translucent material around one end of the toilet paper roll and hold it in place with tape or a rubber band. Try to keep it as smooth as possible over the opening.
Repeat this with the foil on the other end of the toilet paper roll. Then, poke a hole in the middle of the foil with a pin. The hole should be as small as possible. Larger holes will let in more light and therefore help see in lower light conditions, but the image will be blurrier. Best to start with a small hole. However, this is a good area for experimentation: it is easy to replace the foil and try a different hole.
Lastly, fit the translucent end of the toilet paper tube into the paper towel roll. It should fit snugly; any gaps will make it harder to see the image. However, if you do have gaps, don't fret! It is easy to fix.
Test out your camera obscura by pointing the foil end at something brightly lit with high contrast, like a tree outside. If you see a ring of light where the two tubes meet, then the gap can be covered with foil wrapped around it and taped down. When you have fixed the gap, you should see an upside-down image projected on to the translucent material. Sometimes it takes experimentation and relaxation to see it.
So what is happening? When the light bounces off of objects and into the tiny hole, it bends slightly and consistently, causing the image to be projected upside-down. The screen created by the translucent material catches the image so that you can see it. Your eye works the same way except it is WAY more sophisticated, so what you see is more complex. Light that bounces off objects in your view enters the eye through a small hole (the pupil), is focused (by the lens) and caught on the "screen" in the back of your eye (retina). It is also upside-down, but once it travels through to optical nerve to your brain, your brain turns it right side up again.
A camera obscura can be made out of anything, as long as you block out all light except for one pin prick. People have even made them out of entire rooms, and there is one in Santa Monica that is open to the public.
Therefore I couldn't resist making another, this time out of a cereal box. For this one, I used an empty cereal box and liner, tape, scissors, and foil.
I cut the end so that I could fit a piece of foil over it to get a nice clean hole. I also taped up the corners to keep out light.
Then, I cut slits in the top and bottom of the box, almost the width of the box. The slits are a little less than halfway to the other end.
After cutting a piece of the lining to size, I threaded it through the slits.
and taped it securely on both sides, keeping it flat on the inside while not crushing the box.
I added more tape and foil to block out light coming in around the slits.
Then, I peeked through:
As you can see from this photo, it is a little hard to see because the light coming in from the viewing side reflects off the "screen." However, the image is bigger than the tube version, and I could always tinker around to block out more light. The frustrating thing about these photos is that they can't communicate how magical it is to experience this in person, so I recommend you try it!
So there you go! Please email me if you have trouble. Also, if you have a different design, I'd love to see!