A "camera" is, in its simplest form, like a box with a hole in front of it. There is a special piece of glass in front of the hole called a lens. To take a photograph of something, the lens makes a small picture of the object inside the camera. The lens does this by focusing light. A lens in a camera works like a lens in glasses (spectacles) or a magnifying glass. One type of camera called the Pinhole camera has no lens but uses a very small hole to focus light.
To make a photograph with a camera the shutter release button is pressed. Pressing the button opens the shutter. The shutter is like a door. It covers the hole in the camera box. The shutter is behind the lens. When the shutter is closed no light can enter the camera box. When the shutter is open light can enter the camera. When the button is pressed the shutter opens and then closes. This happens very fast. The amount of time the shutter stays open for is called the shutter speed. The shutter speed can change between 1/1000th of a second (0.001 s) to a few seconds. Normally the time taken for the shutter to open and close is far less than 1 second.
Some cameras have an aperture ring. It controls how much light enters the camera box.
The photograph in a camera may be made on film or, if it is a digital camera, using an electronic sensor.
The picture the lens makes is recorded on photographic film. Film is placed inside the camera box. Light coming through the lens, aperture and open shutter shines on the film. Photographic film is coated with chemicals that react when light shines on it. Letting light shine on the film is called exposing the film.
There are many different types of photographic film. There are films for taking colour photographs and films for taking black and white photographs. There are different sizes of film. The most common size is 35 mm. It is called 35 mm because the width of the film is 35 millimetres.
Another difference between films is how sensitive they are to light. Films have a code number, called an ISO number. The number tells how fast a film reacts when light shines on it.
Once the film has been exposed it is processed. Processing has to be done in total darkness or the film will be exposed too much and the picture will be lost. Processing stops the film reacting to light any more. After the film has been processed the picture can be seen on the film.
A photographic print is a photograph made on paper. A light sensitive paper is used. The picture on the film is placed in an enlarger. An enlarger is a machine that shines light through the film and makes a bigger picture on the light sensitive paper. A chemical reaction happens in the paper, which turns the areas hit with light black when the paper is 'developed'. (The more light, the darker the area.) Developing makes the picture appear on the paper – now it is a photograph. Then the paper is put into other chemicals that make it not sensitive to light any more. This is called "fixing". Last, the paper is washed so that there are no more chemicals on it and then dried. Then it is finished.
Digital photography uses a digital camera. Sometimes it is called digital imaging. Like other cameras a digital camera has a lens, aperture, and shutter. The picture the lens makes is recorded by a light-sensitive electronic sensor. A digital camera does not use photographic film to record a picture. Digital photographs are stored in storage devices such as SD cards. They can later be transferred to a computer. Paper prints can also be made from digital pictures. Digital cameras are also not expensive to use, as there is no film to buy.
Taking a photographEdit
One of the most important things when taking a photograph is focusing the lens. If the lens is not focused well, the photograph will be blurry. Autofocus cameras focus automatically when the shutter release is pressed. There are also manual focus cameras (usually older ones).
Three other things are important when taking a photograph. These control how bright or dark the photograph will be.
- The shutter speed – how long the shutter is open for. This is written in the form "1/400," or one four-hundredth of a second.
- The aperture – how big the aperture in the lens opens. This changes how much light is let in. This is written in the form "f/5.6," which describes the ratio between focal length and the size of the aperture opening.
- The film speed – how quickly the film/sensor records the picture. This is also called ISO, and is written in the form "400."
A slower shutter speed, a bigger aperture, and faster film/higher ISO sensor all make a brighter picture. A faster shutter speed, a smaller aperture, and a slower film/lower ISO sensor all make a darker picture. A good picture is not too bright and not too dark. When it is too bright it would be called "overexposed". An automatic camera changes these things by itself when the shutter release is pressed.