The kids and I had some time to build a camera obscura this summer. It wasn’t very hard to do. But it did take some time. We used our entertainment room. By blacking out all the windows with 4mil black plastic we managed to remove all light from entering into the room. This is the key to creating a camera obscura, total control of the light.
Now that the room is completely dark. It is time to allow a source of light into the room. Using a dime for the initial aperture. I cut a hole in the plastic with an exacto-knife, tracing the diameter of the dime. With the dime hole created we were now standing inside of the camera. With the single source of light coming through the hole in the plastic there was a reflected image projected inside the entertainment room. Though difficult to see at first due to the sudden source of light and the fact that the image is upside down and backwards from the source. As your eyes adjust the image from outside the the hole is clearly projected into the entire room.
Setting up a projector screen the image became very clear. With the screen becoming a flat focal plane you could see all of the world outside the hole clearly projected onto the screen. The thing that amazed me was the clarity of the image even without a lens. Also the width of the image. The dime sized hole acted as one of the widest angle lens’s I have ever seen. Amazingly wide. Anything that was outside was clearly visible almost to 180 degrees from the aperture.
Then we decided to create several different apertures to see how that changes the image. First we took a piece of card board an punched a hole in it with a Bic pen. Then taped it up in front of the the dime sized hole. This dramatically reduced the available light into the camera obscura. But the images focus became much sharper. Then we took a black piece of construction paper and placed a jewlers #2 screw driver hole in it. Taped that on top of the hole made wit the bic pen. The image again dropped in lumanance, but in the case the focus was not sharper.