We see like a camera
Do you like taking photographs? Perhaps you have someone in your family who appears on almost every photograph you take. Photographs are so widely used in newspapers, magazines and books that we take them for granted. A hundred and forty years ago the taking of a family photograph would have caused great excitement as photographs were only invented in the nineteenth century.

The first cameras were developed much earlier. The earliest cameras were developed in the sixteenth century and were so large that you sat inside them! A camera of this type was really a darkened room with a small hole in one wall. When light shone through this hole, a picture was formed on the opposite wall. This type of camera was called a camera obscura.

Over the centuries cameras were developed in different ways. Some camera obscuras remained the size of rooms but the hole was equipped with lenses and mirrors. These made a larger, clearer picture inside the camera obscura. The lenses and mirrors could be moved so that they presented different views. Camera obscuras of this type were set up in towns, and people could go inside them and see different views of the town. They could see people and traffic moving which caused great excitement as the only other pictures available to people were drawings and paintings.

Other camera obscuras were made smaller and smaller and became portable. One of these was like a wigwam that was set up over a table. It had lenses and mirrors on the top and the light from them passed onto a table below. Camera obscuras of this type were used by artists to help them make pictures of landscapes.

Perhaps you have used a very small camera obscura. It is called a pin hole camera. You can make one of these from a small cardboard box about twelve centimetres long. Cut a hole in opposite ends of the box and cover one hole with greaseproof paper and the other with a piece of aluminium foil. Make a pin hole in the centre of the aluminium foil and point the camera at a light, such as a reading light. If you look at the back of the camera you will see a picture of the lamp appear on the sheet of greaseproof paper. A picture forms in the pin hole camera because light rays travel in straight lines. Some light rays from the top of the reading lamp, pass through the pin-hole and form part of the picture at the bottom of the greaseproof paper. Some light from the bottom of the reading lamp passes through the pin-hole and forms part of the picture at the top of the greaseproof paper. This change in position of the light rays means that the picture of the reading lamp is upside-down.

The great disadvantage of the camera obscura was that its pictures could not be permanently recorded as a photograph. However, this changed in 1822 when the French inventor Joseph Niepce put a light sensitive material inside a camera obscura and left it for eight hours. The material was made of pewter and was flat like a plate. After eight hours Niepce found that a photograph had formed on it. These flat devices on which photographs formed became known as photographic plates. After Niepce's discovery, many scientists began working on improving photographs and cameras. In 1839 Louis Daguerre used a photographic plate made of copper to take the photograph of a person. The person only had to pose for a minute while the photograph formed on the plate. Until about 10 years ago, cameras took photographs onto a roll of film. Today, cameras take photographs in a fraction of a second and the photograph forms on a small piece of light-sensitive chip.

Next time you take a photograph think what happens when you press the button on the camera. A door, called the shutter, behind the lens opens for a fraction of a second. Light rays pass through the lens and through the door to form a small, upside-down picture of the view in front of the camera. The energy in the light making the picture causes changes in the detector which is then saved onto a chip inside your camera or phone.

What does a camera lens do?
It gathers light from the view and directs it onto the film at the back of the camera. A lens is made from transparent glass or plastic. It has a bulging or convex surface. If a light ray strikes the centre of the lens it passes straight through to reach the detector. If a light ray strikes other parts of the surface away from the centre the lens bends its path so that the rays come together on the detector and form a clear picture or image of the view.

Can a lens on an ordinary camera gather light from any distance?
No. It can gather light from the horizon down to a metre or so in front of the camera. It cannot gather light close to the camera and form a clear image on the film. Special lenses can be fitted to some cameras so they can take pictures of objects which are very close to the camera. Photographs of insects are made in this way.

Some cameras have settings for sunlight and cloud. What are they for?
The quality of a photograph depends on the amount of light that enters the camera. A poor photograph will be made if too much light or too little light enters the camera. The amount of light entering the camera depends on the size of the hole behind the lens. If the hole is large and a photograph is taken on a sunny day, too much light will enter the camera and this will spoil the photograph. If the hole is small and the weather is cloudy, too little light will enter the camera and this will also spoil the photograph. When you set the camera for bright sunlight, a small hole is made behind the lens, which prevents too much light entering. When you set the camera for cloud, a large hole is made behind the lens to allow more light to enter the camera and form the photograph.