Why doesn't my pinhole camera work?

Question

We all know that light travels in straight a line, which can be proved by pinhole imaging as in the picture shown :

But when I'm doing this little experiment with an apple, no matter how I change the distance between the object and the pinhole, an image can never be observed on the cardboard behind. So what's going wrong? Please help!

Answer 1

It actually is providing an image, you just cannot see it because of contrast. The light you have in the picture is flooding the room with enough ambient light that the image that is actually formed has no contrast.

1. Pinhole camera image quality heavily depends on the pinhole size. However, the smaller the pinhole, the "dimmer" the image will be, this is the problem that you have.
2. In order to be able to view the image you will need to make the pinhole basically in a box. The box could be an entire room (e.g. cover all windows in a room with aluminum foil so it is very dark, then prick a pinhole in the foil on one of the windows) or a smaller box with a "viewing screen." The key think is that whatever "box" that you use needs to be relatively dark inside.

A viewing screen can be something clear but diffuse, like parchment paper or privacy glass. Even with the viewing screen, you need to somehow make it dark enough so that your eyes can see it.

You could also make an enclosure large enough for you head to fit into, but still maintain a good level of darkness.

If you have an old webcam, this might work inside of an enclosed box, then you can view the image on your computer.

This is one of the things that makes using pinhole cameras in demonstrations difficult, you want the object being imaged to be well lit, but you need the viewing screen to be dark.