The simplest way to project an image onto a screen is with a pinhole. What the heck is a pinhole? It's a hole so tiny it has to be made with a pin. See, science isn’t that hard.
People have been building image viewers with this trick for hundreds of years; it was originally known as a camera obscura, which means “dark chamber.” The idea was, you get some people in a dark room with only a tiny hole open to the outside. It seems magical, but the light from that hole would project an image of the outside world onto a wall in the room.
Of course, later on, if you didn’t want to get in a dark room, you could replace the people with chemical film, and boom: You had a pinhole camera. I’m going to go one further today and build a pinhole video camera. You can do it too! I have a video at the end of this article that will show you how, using basic materials you have at home.
But first, how does it all work? Let's start with some simple experiments to find out.
With a Point Light Soruce
In fact, let’s go back to the simplest possible case. What happens if I have a point light source in front of a barrier with a pinhole in it. Here is a diagram:
Most of the light rays go off in different directions and have their own story in some other blog post. Some of them hit the barrier and bounce off or get absorbed. But a few, at just the right angle, get through the hole to the viewing screen. These rays then reflect off the screen and give the appearance of a bright spot.
Now let’s take it up a notch. What if I have two lights? Suppose I put an orange light above a green light, about 6 inches apart. What will appear on the screen? This isn't too hard to set up. I taped two LEDs to the ends of a pencil and used button cell batteries to light them up: