Category Everyday Science

With a modern camera, you need do no more than press a button to take a photograph – to snap the action of a sporting event or record the beauty of a prizewinning rose, for example –and make a permanent record of a fleeting moment.

Technology has taken the guesswork out of the picture taking, there are now computerized automatic cameras that focus themselves, set their own controls, and wind-on the film after each shot. In contrast there are also simple throwaway cameras that are disposed of once the film has been processed.

All cameras, no matter how sophisticated or how simple, work in much the same way. When you click your camera to take a picture, you are opening the shutter for a brief moment to let light through the lens to a dark interior. In this moment, the light rays from an inverted image of the scene in front of you on the light-sensitive film at the back of the camera.

Processing the film completes the chemical changes begun by the light striking the film, and printing the film provides a pictures of the scene you snapped.

 

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Sunlight is broadly made up of the three primary colours of light: blue, green and red. All colours can be made by different mixtures of the three. Pairs of primary colours produce secondary colours: magenta (blue and red), yellow (green and red), and cyan (green and blue). If secondary colours are paired, they produce the primary colours. Magenta and yellow make red, cyan and yellow make green, cyan and magenta make blue. Each of the six colours takes no part in making up the colours opposite to it in the charts. Blue and yellow are ‘opposites’, so are green and magenta, and red and cyan.

Negative and print

A colour film has three layers, each sensitive to one of the primary colours. When a photograph is taken, each layer records a primary colour but forms an image in dye of the opposite colour to the primary.

The negative is then printed by light in a darkroom on paper that contains similar colour-sensitive layers. When normal light passes through the blue wheel on the negative, the yellow dye blocks the blue rays but lets through the red and the green. The paper records the red and green cyan and magenta dyes (their ‘opposites’). When you look at the photograph the combination of cyan and magenta appears blue. All the other colours are produced in the same way.

 

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When you take a photograph the subject that you see through the viewfinder is recorded on the film during the brief moment that the shutter opens to let in light through the lens. The film is coated with an emulsion that is chemically affected by light. ‘Fast’ films are more sensitive to the light than ‘slow’ films, so can be used in duller conditions. The speed of the film is indicated on the box and the spool by the ISO number. The higher the number, the faster the speed.

The camera lens concentrates light from the subject of the photograph and projects an inverted image of it onto the film at the back of the camera.

The diaphragm has overlapping leaves that form an aperture which can be made larger or smaller. A big aperture lets more light enter the camera.

A common type of shutter has two blades that open to form a slit that crosses the film. The smaller the slit, the faster the shutter speed.

 

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Busy executives and technicians can carry their own personal buzzer – rather like a pocket electric bell – to warn them which they are wanted. Doctors on their rounds in a sprawling hospital, for example, can be called to a particular ward, or firemen on routine duty to a fire alert.

The pocket alarm, known as bleeper (or beeper) because of the sound it emits, to a battery-powered miniature radio receiver turned to one station. The bleep is made by a tiny crystal that vibrates to produce sound when electric signals are passed to it. The signals are generated in the bleeper’s electronic circuits, triggered by a radio signals transmitted at the touch of a button from the control unit.

The simplest bleeper can emit several different signals, rather like the dots and dashes of Morse code. Four long bleeps, for example, could mean ‘Ring the office’, or interspersed long and short ones ‘Come to reception’. More advanced types can display short message, or can store messages.

The system is known as radio-paging. A small network can call up to about 100 receivers, either separately or simultaneously in a group. Each receiver has a number, and the controller makes contact by sending the receiver number and then the required message.

Long-range paging services are operated by commercial companies who transmit messages to their subscribers’ bleepers from a control room. The world’s largest paging network is operated by British Telecom, who have transmitters covering various zones throughout the country.

Radio-paging systems all have to be licensed, and are allocated a frequency, generally around the 27mHz waveband in Australia. The operating range varies according to the power of the transmitter but could be 100 miles (160km).

 

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Newspaper have been using facsimile machines to send photographs (wire photographs) since 1907, when a photo from Paris was wired to the Daily Mirror in London. In 1959, a Japanese newspaper Asahi Shimbun
(‘Morning Sun’), sent whole pages from its main office in Tokyo to a printing works at Sapporo 600 miles (960 km) away. Now it sends a complete copy daily by satellite link to London, where it is printed, for sale in Europe.

In recent years, technological advances have resulted in cheaper machines able to give good quality reproduction. Newspapers and business firms are not the only users. Police forces can send each other copies of fingerprints and photo fit pictures.

The earliest fax machines took about six minutes to transmit a document the size of an A4 typing sheet. Later machines cut the time by half. Modern machines take less than 30 seconds. They code the information digitally although it is transmitted as analogue (like sound-wave) signals. Machines available in the 1990s will both code and transmit digitally, cutting A4 sheet transmission time to four or five seconds.

 

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Telephone cables carrying messages at the speed of light have given a new lease of life to telecommunications. The amount of information now transmitted – telex, fax and computer data as well as telephone calls – was straining the copper-cable system to the limit. Fibre optic cables, with thir high capacity, small size and freedom from electrical interference, are the key to development.

The first uses of optical fibres was in medicine in 1955, for lightning up parts of the inside of the body. The light loss through the fibres was at first too great for many other uses. But in 1966, Dr Charles Kao and Dr George Hockham, two scientists working in Britain at the Standard Telecommunications Laboratories, discovered that the loss was due to impurities in the glass. By 1970, due to impurities in the glass, Corning Glass, had produced fibre optics good enough to transmit telephone signals.

Fibre-optic cables are now gradually replacing copper ones between exchanges. The first transatlantic fibre optic cable, TAT-8 – jointly laid by American, French and British companies – began service in 1988, its capacity of around 40,000 simultaneous telephone calls is three times as great as the seven existing copper transatlantic cables put together.

 

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