Cameras and photography
A view inside a digital single-lens reflex cameraA camera is a device that records an image of a scene, either electronically as a digital photograph or on photographic film. The main features of a camera are a lens and a shutter. Light from a scene is let into the camera when the shutter opens. The lens focuses the light on to the back of the camera. In this way it makes a small copy of the scene called an image. The image is captured on a charge-coupled device (CCD) or on a strip of photographic film. Today most cameras are digital, and digital cameras are often incorporated into devices such as smartphones.
How a camera works
A camera's main features are a light-proof body, a lens and a shutter. The lens gathers rays of light from the scene that the camera is pointed at and bends them so that all the rays from one point on the scene are focused to meet at the same place at the back of the camera. In this way it makes a small copy of the scene called an image. The shutter opens to allow light from the lens to reach the light sensors or film. The shutter speed (how long the shutter opens for) and size of the aperture (an opening behind the lens) can be adjusted to regulate the light sensor or film's exposure to light.
Digital cameraA digital camera is a camera in which photographs are stored electronically in digital form rather than on traditional film. The lens focuses the light on to a special microchip, called a charge-coupled device (CCD). This divides the image into thousands of pixels, measures the brightness and colour of each one, and digitizes the readings. The digitized image is stored in memory chips or cards, or on a disc. The photographs are transferred to a computer. Here they can be viewed on screen, edited, added to documents, used to make greetings cards, attached to emails or uploaded to social media or other cloud storage websites.
Single-lens reflex camera
A film single-lens reflex camera in cutawayA single-lens reflex camera is often known as an SLR. It allows a greater range of photographic effects to a compact (point-and-shoot) camera or a camera phone, because the photographer can manually control functions such as the focus, exposure and flash. A digital single-lens reflex camera (DSLR) combines the workings of a single-lens reflex camera with, instead of film, a digital "back": a charge-coupled device (CCD) to capture the image. In an SLR, a mirror and a pentaprism reflect the light from the lens into the viewfinder so that the photographer sees exactly what the image will be. When the shutter-release button is pressed, the mirror flips up out of the way and the shutter opens to let light reach the CCD or film.
The fastest production camera is the streak camera. It is used in scientific and industrial research. The streak camera can reveal what happens when a high-speed bullet hits a target, for example. Light entering the camera is converted into an electron beam (like the inside of a cathode-ray tube). This forms an image that can be recorded on a screen. There is less than one trillionth of a second between each image, which means that a sequence of a trillion images could be taken in one second—fast enough for scientists in December 2011 to capture images of a beam of light travelling through a plastic bottle.
Recording an image on film
Nowadays, most people use digital technology rather than film—but some professional photographers still use film, believing that its range of light and colour effects are as yet unmatched by digital cameras. Photographic film consists of a plastic strip coated on one side with a layer of light-sensitive chemicals. When light from a scene is focused on to the film in a camera, the chemicals in the bright areas of the image begin to change. The brighter the light, the greater the change. The chemicals remain unchanged in the dark areas. At this stage, the image is simply a pattern of chemicals. It only becomes visible when the film is processed. Colour film contains three layers of chemicals, one to record each of the primary colours of light, which are red, green and blue.A dark room Film is processed, or developed, in a dark room. Dark rooms are often lit by red light, because most photographic paper is sensitive only to blue and green light. During the developing process, photographic film or paper is chemically treated to create a fixed image. It is first soaked in chemicals called developer, which reveal the images. Then it is soaked in a stop bath to halt the developer, and then finally washed in water.
Consultant: Chris Oxlade