Smile please, for our PINHOLE CAMERA What you’ll need: • Toilet roll • Tracing paper • Black paper / marker pen • Drawing pin • Magnifying glass • Masking tape / elastic bands What to do: • Cover one end of a toilet roll with black paper. • Cover the other end with tracing paper. • Make a small hole in the black paper. Start with a small hole. Face the hole to a light source and watch the window. Increase the size of the hole, and use a magnifying glass to make the image in focus. • A small hole will give you a sharp image. A large hole means more light will get in from different directions, which will lead to a less focused image. Using the magnifying glass will allows you to focus the light better. What's happening? The diagram below illustrates how the projection pinhole camera works. The light enters the small pinhole in the front of the camera, and projects onto the wax paper screen (blue line). The image the person sees projected onto the wax paper is upside-down and backwards. The cartridge camera works the same way, but instead of having a wax paper screen, the image projects onto film. Ideally, the pinhole in a pinhole camera would be small enough so that only a single "ray" of light from each point of the object would be allowed to reach the screen. This would create perfectly sharp images. Unfortunately, even if this were possible, the images thus produced would be very dim, and would be difficult to see in our camera. (In the cartridge camera, it would require long exposure times, allowing the image to blur due to motion of the object being photographed.) To create a brighter image, we can increase the pinhole size, allowing more light in. This blurs the image, because "rays" of light from the same point on the object traveling in slightly different directions would all be allowed to enter the camera. It's an upside down world... Note that image formed on the screen is upside down. The same thing happens to images that form on the retina at the back of your eyes. Hmmmm – so how come we don’t see the world upside down? The answer is that our brains ‘know’ to reverse the incoming images, so that up is still up and down is still down. But that hasn’t stopped psychologists from experimenting with the phenomena. Experiments have been recorded in which subjects were asked to wear up/down reversing prisms on their eyes to explore whether their brains could cope with a "real" upside down view of the world. And the answer was: after several days of banging into things, yes, the subjects’ brains were able to readjust, so that the world looked the right way up again… Go back