I made these little gadgets when I was a kid and had access to a darkroom and light-sensitive film, but here's my attempt to bring the camera obscura to the digital age, using my cell phone instead of film to record the image.
The result? Well, hum, zero in terms of the advancement of science - but I did manage to combine one of history's most advanced cameras with the most primitive, which is kind of neat. Anyway, it was a fun morning's project and might be useful for anyone out there teaching optics.
Step 1: What Is a Camera Obscura?
A camera obscura, or pinhole camera, is the earliest form of camera. It utilizes the principles of optics to project an image through a tiny hole, which functions as a basic lens. Early cell phone cameras functioned exactly the same way, incidentally.
Step 2: Start With a Box...
A pinhole camera is a box with a pinhole through one side. So you will need a box.
For an effective camera, there should be no internal reflections. Paint the inside black and seal up all the cracks (I used black electrician's tape). Paint the internal wall facing the pinhole white, to form your projection screen - or glue in a square of white cardboard.
Note that in the photo above, even without the pinhole or closing the box, the apartment opposite mine is already projected on the back screen through the rough hole I cut for the lens. Pretty cool. It gets better.
Step 3: Make a Pinhole
Take an ordinary washer and glue some aluminium foil to it. When it is dry, poke a little pinhole through the centre of the foil with a needle (or a pin, if you insist). This is your lens. You could just poke a hole through the box I suppose, but foil works better.
Glue the lens over the top hole you cut in the box (being careful not to damage your tiny pinhole).
Step 4: Mount the Pinhole
Cut a couple of holes in the box facing the projection screen wall on the inside. One of the holes will hold your lens, the other will be the opening you set your cell phone camera up to. The phone is mounted on the front of the box, facing backwards towards the projection screen.Yes, it is a bit clumsy.
Step 5: Add a Cell Phone
Attach your cell phone to the other hole (just below the pinhole) with tape or an elastic band so that the camera is viewing into the box towards the projection screen.
Now, cell phones are not good at long exposure photography, and the dim light projected by the pinhole is not easily picked up by the phone camera. You will need to download an app, but the good news is they are free. Search for a variant on "slow shutter cam". Then position your pinhole camera somewhere pointing at a scene with good lighting, and experiment with exposure times. Depending on your app, and the ambient light, it should take around 2-15 seconds. You are ready to make your first blurry historic image. Yay photography!