My Science School

Although the helicopter in its present form is scarcely 50 years old, the principle of the rotary wing has been known for centuries. The Chinese used it some 2500 years ago for their flying top — a stick with propeller-like blades on top which was spun into the air. And Leonardo da Vinci actually sketched a helicopter in 1483. The English flight pioneer Sir George Cayley was among several people to design a model helicopter in the late 1700s, but the first man-carrying helicopter, which rose a few feet in the air, was not built until 1907 — by a Frenchman, Paul Cornu, at Lisieux. Problems with stability and other design aspects led to helicopters being abandoned for nearly 30 years in favour of fixed-wing aircraft. Many of the design problems were, however, solved by the Spanish inventor of the autogiro, Don Juan de la Cierva, in 1919. This aircraft had a large rotor that was not driven by the engine but turned freely in the airflow. It could not take off vertically — it had to taxi to get the rotor turning enough to lift it.

Not until 1936 did the German Professor Heinrich Focke, of the Focke-Wulf Company, design a practical helicopter with twin rotors. Three years later a Russian-born engineer, Igor Sikorsky, produced a successful single-rotor helicopter, the VS-300, in the USA. This was the true ancestor of the modern rotorcraft — the most versatile of aircraft.

The development of jet engines in the 1950s led to the adoption of turboshaft engines that have considerably increased the range and speeds possible. Today the helicopter is invaluable not only as a military transport, hedge-hopping patrol plane and sky crane — for lifting steeples onto churches, for example — but also for rescuing people from remote mountainsides, sinking ships and burning buildings.

 

Picture Credit : Google

Submarines often travel in the ocean depths for weeks on end. They do not need to surface to check their position by the Sun, Moon or stars, because the latest navigation systems allow them to know where they are to within less than 320ft (100m) of their actual position while still submerged.

 These systems are known as inertial navigation systems and are computer-controlled. There are usually at least two on a submarine, operating independently. They are a modern version of 'dead reckoning' — calculating where you are by measuring exactly how far you have come from your starting point, and in what direction.

The inertial navigation system is held absolutely horizontal and pointing in a fixed direction by gyroscopes, whatever the attitude of the submarine.

 At the start of the voyage, the instruments are fed with the submarine's exact position. An accelerometer then measures movement in every direction, and the computer works out the overall distance and direction travelled, thus establishing the present position.

Sonar is used to determine the water depth below the vessel to prevent it running aground. Inertial systems are on the whole accurate, but the small errors they do make gradually accumulate. They have to be realigned regularly. This is done by picking up radio signals from satellites in space, which form part of the American NAV-STAR Global Positioning System (GPS). The submarine has to partly surface.

 The satellites transmit a radio message which contains precise details about their orbit, and a time signal controlled by an atomic clock. In effect, the signal says 'It is now time X'. The submarine uses its own clock to calculate how long it takes the signal to arrive. As radio waves travel at 186,000 miles (300,000km) per second, the navigators can calculate the sub-marine's distance from the satellite by the time the signal takes. By calculating the distance from three GPS satellites, the ship's position can be pinpointed on a chart.

During the 1990s, the last 04 18 satellites in the GPS system will be placed in orbit at a height of 12,500 miles ,20.000km), orbiting the Earth at 12-hourly intervals. They will ensure that at any time at least four satellites will be available for navigators to calculate their position to within 550yds (500m;

The GPS system has virtually replaced older forms of submarine navigation such as the OMEGA system, but submarines still carry it as a back-up. This system detects radio signals broadcast from eight stations dotted around the Earth's surface — in Japan. Hawaii, Australia, Argentina, North Dakota. Norway. Liberia and Reunion Island. These stations broadcast at very long wavelengths, so their signals carry all around the world. The signals are synchronised, and by measuring the time differences in their reception, a sub-marine's position can be estimated to within about miles (3.2km)

 Inertial navigation also mounted in long-range intercontinental launched from submarines .

 

Picture Credit : Google

Medieval castles had all sorts of traps pitfalls to keep out intruders. Homes of today can have an equal number of defences, without having to resort boiling pitch. Modern defence devices include floodlights or alarms that are triggered when an intruder upsets a circuit monitored by hidden magnets or micro. chips, or by invisible beams.

The outer defences

The modern burglar might first have to face  a strategically placed invisible infrared detector that is affected by temperature changes caused by body heat. When anyone approaches the house, a sensor in When the detector switches on floodlights. If the caller is legitimate, the lights show the Way but anyone planning burglary will feel very exposed and less likely to continue.

The sensor is pyroelectric — that is, made from a ceramic material such as tourmaline, which, when heated, generates a voltage across it. The system is designed so that the sensor will respond to a temperature change caused by human body heat, but is less likely to be set off by changes in the weather.

 A burglar who dodges a floodlight - barrier may then face a door connected to a noisy alarm. A magnetic switch IL inserted between the door and its frame. When the door is shut, two contacts keep switch circuit closed. This switch is monitored electronically by an alarm circuit. If the door is opened arid switch circuit is broken, the alarm circuit triggers the alarm.

But a resolute burglar, out of sight of passers-by, might attack the door with a chisel or drill. This type of attack can be foiled by a vibration detector fitted to the door. This is a device in which a ball is disturbed by vibrations. The ball rests on sharp metal points wired to a microchip that is programmed to accept certain vibrations — such as those caused by wind or passing traffic — as normal. If the ball bouncing on the points sets up vibrations not in the program, it sets off the alarm.

The inner defences

If the burglar succeeds in getting through a door or window, he may face a battery of inner defences. These include pressure Dads concealed under the carpet and inked to an alarm circuit. They have two metal plates or foil sheets separated by a layer of spongy plastic. The two plates are pressed together if anyone treads on them, and this sets off the alarm.

Anyone who prowls around inside the house may be caught by a 'magic eye'. This is a photoelectric cell with an invisible infrared beam shining onto it. If the beam is interrupted, the photocell triggers an alarm.

Other types of indoor detector use either ultrasonic waves (too high pitched for humans to hear) or microwaves (high-frequency radio waves) transmitted by

devices called transducers. They transmit the waves at a certain frequency (a given number per second), and the waves are reflected back to the unit from objects in the room. If anyone moves through the room, the reflected waves get bunched up or pulled apart, so their frequency is altered. The sensor detects the frequency change and feeds signals to a microchip which assesses the speed and bulk of the intruder. Anything assessed as typically man-sized makes it set off the alarm.

A commoner type of indoor detector uses an infrared system similar to the outdoor floodlight type. in the detector. a many-faced mirror or special lens creates a number of sensitive zones. If anything moving in and out of these zones is at a different temperature to the room surroundings, it generates a voltage. The detector electronically monitors the voltage, and is designed to set off the alarm if the temperature increase is likely to be caused by human body heat.

 

Picture Credit : Google

When lightning struck the roof of York Minster, one of Britain's finest medieval cathedrals, in 1984, it started a fire that was if trapped between the ceiling and the wooden roof. Firefighters could not get into the area, and the enormous heat that built up destroyed most of the roof.

If lightning should strike York Minster twice, space-age science has ensured that the same type of damage will not happen again. The new roof is fitted with trap doors to let the heat out and the firefighters in, and the doors have latches operated by springs made from memory metals, which will open automatically if they get hot.

Memory metals have two different shapes they can 'remember', and will switch from one to the other under certain conditions. The York Minster trap-door springs are made to remember a certain temperature, at which they will expand and withdraw the bolt, releasing the door.

One of the first uses of memory metals has been for hydraulic pipe couplings in aircraft, which came into use in 1971. The couplings are made too small to fit at a certain temperature, and are then cooled to well below room temperature and stretched to fit. When they warm up to their normal operating temperature, they shrink to the first shape, forming a tight joint. The same idea is used in surgery, with metal couplings to bind together broken bones. Body heat keeps them constantly tight.

Metals that change their shape under heat now have all kinds of uses, such as operating switches and valves in automatic coffee machines, and opening greenhouse windows when it is hot and closing them when it is cold. Most metals are made up of crystals (arrangements of atoms). When two or more metals are combined into an alloy, the alloy can form different crystal structures under different conditions.

Some alloys, if they are cooled rapidly, will undergo an abrupt change to a different alignment of crystals at a certain temperature. This transition temperature varies with the make-up of the alloy. The changed structure it brings about is called martensite, after the German metallurgist Adolph Martens who first identified it.

If such an alloy is shaped by heat treatment so that it becomes martensite at, for example, 122°F (50°C), it will change its shape at that martensitic temperature, but revert again at a different temperature.

Shaped for shaping

A Japanese company has found an unusual use for memory metals — as a super-elastic wire frame in brassieres. The alloys used will stretch up to ten times more than ordinary metals. When stretched in use, the bra wire gradually returns to its original bust-supporting shape.

Another use for super-elastic wire is in straightening teeth. Conventional stain-less-steel wires have to be regularly tightened, often by turning a tiny key. Super-elastic alloy wires exert a continuous gentle pressure ideal for coaxing teeth in the right direction.

 

Picture Credit : Google

When someone blows into a breathalyzer bag, any alcohol in their breath is turned into acetic acid (vinegar). This chemical reaction changes the colour of the crystals in the blowing tube. The more crystals that change colour, the more alcohol they have in the body.

The first breathalyzer was developed by an American doctor, Rolla N. Harger (he called it a 'Drunkometer'), and it was introduced by the Indianapolis police in 1939. Similar breathalyzers began to be widely used by the police in many Countries in the 1960s, as a yardstick for judging a driver's ability to drive. A high Intake of alcohol dulls the nervous system and slows up coordination.

To begin with, the commonest type of breathalyzer was a plastic bag, similar to a balloon, with the crystals in the blowing tube. and the driver was asked to inflate the

bag. If the crystals changed colour as far as a level marked on the tube, the driver was possibly 'over the limit', and needed further tests. The crystals used were an orange-yellow mixture of sulphuric acid and potassium dichromate. They turned the alcohol into acetic acid (vinegar), and in doing so they were changed into colourless potassium sulphate and blue-green chromium sulphate.

The breathalyzers used by the police today, however, are usually electronic, and much more accurate than the inflatable-bag type. They use the alcohol blown in through the tube as fuel to produce electric current. The more alcohol the breath contains, the stronger the current. If it lights up a green light, the driver is below the legal limit and has passed the test. An amber light means the alcohol level is near the limit, a red light above the limit, and in both cases  the driver has failed the breath test and needs further testing.

This type of breathalyzer is about the size of a TV remote control, and contains a fuel cell that works like a battery. Breath from the tube is drawn into the cell through a valve, and meets a platinum anode (a positive plate). which is against a spongy disc impregnated with sulphuric acid. The platinum causes any alcohol in the breath to oxidise into acetic acid — that is, its molecules lose some of their electrons. This sets up an electric current through the disc, and it flows to a cathode (a negative plate) on the other side.

 

Picture Credit : Google

Most drivers have experienced the frightening moment when the wheels lock and the car slides uncontrollably toward the vehicle in front. Although drivers ate taught to leave a sufficient gap for braking, and to take extra care on wet or icy roads, the huge number of rear-end collisions every year is ample evidence they do not.

Skidding and sliding happen because the behaviour of a car changes rapidly when the wheels begin to lock. Up to a point, pressing the brake pedal harder produces greater deceleration. But once the wheels have locked, their grip on the road is lost, they begin to slide instead of turn, and the driver can no longer control the car's direction. Panic follows, and the natural reaction is to stamp ever harder on the brake, which makes things worse.

Advanced driving manuals recommend cadence braking, in which the brake pedal is pumped up and down in quick succession to ensure that the wheels never lock. But, in practice, few drivers have the skill or experience to do this in an emergency.

Anti-lock brakes are designed to auto-mate the technique of cadence braking, taking the skill out of the hands and feet of the driver and entrusting it to a package of electronics and hydraulics. They consist of two parts: an electronic sensor that can detect how rapidly the wheels are decelerating, and a system for automatically controlling the hydraulic pressure on the brakes to achieve the best and safest deceleration.

The sensor consists of a slotted or toothed exciter disc attached to an axle or inside a brake drum. As the axle turns, each tooth and gap in this disc pass close to a monitor and generate a current, which varies according to the rate at which the disc is rotating.

The signals are interpreted by electronic circuits, which determine both the speed of the disc and the rate at which it is decelerating. If the disc is slowing down too rapidly and is about to lock, the circuits instruct the hydraulic controls to reduce brake pressure, preventing a skid. As the driver continues to press the brakes, pressure rises again, and the system repeats the operation until the vehicle has stopped. The system can produce up to 45 cadences a second, if required.

The details of how the electronic signals are used to control brake pressure depend on individual designs. Some of earliest non-skid brakes, in the 1960s, were fitted to trucks, which use air under pressure to activate their brakes. In these systems it is relatively simple to bleed off some of the air through a valve to reduce pressure. The air lost can easily be replaced by drawing on air stored under pressure in the vehicle.

The same simple arrangement cannot be applied to cars, which use hydraulic fluid. This is because there is little fluid in reserve, and also it would be both expensive and dangerous to spill bled-off hydraulic fluid all over the road. One alternative is to reduce pressure by briefly increasing the volume of the hydraulic system — with a piston arrangement, for example — and then to restore pressure again. Among the systems that have been developed are some that even allow sharp turns to take place safely during heavy braking.

Although anti-locking brakes were originally available only on the most expensive cars, they are increasingly becoming standard, or optional, on most new cars.

 

Picture Credit : Google

The Czech playwright Karel Capek introduced the name robot in the early 1920s. He wrote a play called Rossum's Universal Robots in which an army of industrial robots became so clever that they took over the world. Capek coined the word robot from the Czech robota, which means 'slavery'. Since then men have worried not so much about robots taking over the world, but more about robots taking over their jobs.

Robots have indeed taken over some jobs — dull, mechanical, routine work. They save costs because there is no need for them to change shifts, they do not tire or lose concentration, they do not take tea or coffee breaks, they do not fall ill (although they may need repairs), and they do not go on strike. But even though American and British researchers have produced robotic four-fingered hands capable of picking a flower, robots are still a long way from having the perception, dexterity or flexibility of human beings.

 It is, however, generally accepted that the responsible use of robots in industry is beneficial because it saves people from doing dull and dangerous jobs. Robots were used to clear up the radioactive debris after the Three Mile Island nuclear accident in America in 1979. They are also being developed for inspecting and manufacturing nuclear plants, fighting fires, Felling forest trees, and acting as security guards — walking burglar alarms that can warn human guards of an intruder. And I four-legged, 72 ton robot was used to roll boulders to build up the sea wall in Tokyo Bay, Japan, in 1986 — saving 50 divers from the risky task.

Experiments are also under way with robots that can help infirm and disabled people to be independent. Researchers in Britain and America are developing robots that can respond to spoken commands. They will be able to undertake such tasks as brushing teeth, serving soup, loading a computer, opening filing cabinets and picking up mail.

 

Picture Credit : Google

American motorists were able to buy petrol with oil company credit cards before the First World War, but the age of the credit card dawned in 1950 with the introduction of the Diners Club charge card by American businessman Frank McNamara. The idea came to him after dining in a New York restaurant and discovering he had mislaid his wallet. The Diners Club card is not strictly a credit card because the whole bill has to be paid when the invoice is received — most other cards carry forward a debit balance.

Today there are more than 350 million credit or charge cards in use in the United States alone. Worldwide, cards are numbered in billions.

Smart cards are likely to have a wider use than for money transactions. in the late 1980s some medical authorities in parts of Europe, the USA and Japan began trials with medical identity cards —smart cards carrying the holder's medical history. The cards save time and paperwork, as they can be consulted by doctors and chemists in computer terminals at hospitals, surgeries and pharmacies, and updated each time the patient is seen. The European trial programmes aim to produce a standardized EEC care or health smart card for use in the 1990s.

Also available are laser cards, developed in the USA, in California. They are not as smart as smart cards, but are able to carry a much larger store of personal information, contained in a pattern of tiny holes — only a thousandth of a millimetre across — on a photosensitive strip. The dots, like the pits and flats on a compact disc, can he read by a laser scanner in a special terminal.

The card can hold coded identification details, including fingerprints, signature, voice print, and even a photograph,' as well as various hidden security codes making it -virtually impossible to counterfeit Its information storage space is so vast there is plenty room for such things as bank accounts, medical history and educational attainments. Information is filed on the card under separate access codes, so the bank, for example, could read out only financial information and the doctor only medical information.

 

Picture Credit : Google

Every successful shopkeeper needs to know which goods are selling well and which are going slowly, so that he can restock or phase them out, as appropriate. For the small shop, tidy bookkeeping and a glance at the shelves may give all the information necessary. But supermarkets and other big stores need quick and accurate records of a much larger flow of merchandise. That is why they use bar codes, which are printed on the packaging.

A bar code can be read by a laser scanner, which passes it to a computer. This supplies the details and price of the goods, records the sale for storekeeping, totals the bill, and feeds the information to the cash register which prints out a receipt.

Common bar codes are European Article Numbers (EAN), based on a number with 13 digits, and Universal Product Code (UPC), based on a number with 12 digits. The Australian Product Number (APN) is also based on 13 digits. Each digit is represented by a series of parallel straight lines and white spaces. The laser scanner translates the information into binary digit signals, which it feeds to the computer.

The code gives the manufacturer details of the product and the package size, and includes a security code that prevents anyone altering it or the scanner misreading it. The computer supplies the price from the product information. So the only way to change the price of an item is by altering it in the computer.

 A laser scans a bar code with a beam of light passed from one end to the other. It is sensitive enough to read from left to right or right to left. Although the bar codes are usually printed in black on a white background, a laser can read a bar code which is printed in any dark colour except red, and the background can be any pale or pastel colour. Some of the lasers used scan with red light, so cannot pick up a reflection from red.

Bar coding is faster and more accurate than other systems. Human error is limited because staff do not have to mark a price on every item, and checkout assistants do not have to key in prices at the register. However, because the computer sup-plies the prices at the checkout, the store management has to ensure that the goods on the shelves display the same prices. Also that the shelf price is changed if a computer price is altered, or a customer may appear to he charged the wrong price.

 

Picture Credit : Google

Chips are produced several hundred at a time on a slice of ultra pure, artificially formed silicon crystal, so thin that it would take about 250 slices to form a piece 1in (25mm)thick. Layout diagrams for circuits are prepared on a computer, then each reduced to chip size and set out side by side on a glass plate known as a mask. Because witches and other components are built up in separate layers on the chip, a mask is made for each operation. The masks – which block out the unwanted parts – are made many times larger than the chip and reduced photographically.

The chips are built up by forming each layer – p-type or n-type layers or insulating layers of silicon dioxide – and etching out the unwanted parts. This is done by treating the layer with a coating sensitive to ultraviolet light, masking it, then exposing it to ultraviolet light. The exposed parts become resistant to acid, but the blocked-out parts do not – they are etched away when the layer is coated with acid.

Parts such as aluminium contacts are deposited in the areas etched for them as a vapour. When hardened, the aluminium is etched to add the required circuit connections, which lead to contact pads at the edges of the chip.

All completed chips on slice are tested with delicate electrical probes to check that they are working properly. About 70 per cent prove faulty. They are marked as rejects and thrown away. After testing, the slice is cut into individual chips under a microscope with a diamond-tipped cutter. The good chips are each mounted in a frame that is encased in plastic. The contact pads are linked to metal connectors are in turn linked to protruding legs, or pins, that plug into the external circuit.

 

Picture Credit : Google

Transistors are the commonest components in a microchip. They are used mostly as switches, letting current through to represent the binary digit 1, or cutting it off to represent 0.

A widely used type of transistor has two islands of n-type semiconductor in a larger base of p-type. While the transistor is switched off. The free electrons from the layers drain into the p layer and are absorbed by the free holes. The transistor is switched on by applying a voltage from a separate low-power circuit to an aluminium gate above the p base. This voltage attracts the free electrons from the p base towards the gate. They then form a bridge between the two n islands and provide a path for the current through the circuit in which the switch is operating.

The transistor is switched off by cutting off the power. The free electrons then drain back to the p base and are absorbed by the free holes. Without the bridge they formed between the islands, current cannot flow through the circuit.

 

Picture Credit : Google

Pure silicon is an insulator — it does not conduct electric current However, if it is impure — containing certain other elements — it will conduct a weak current. So it is called a semiconductor, halfway between an insulator and conductor. Semiconductors allow the delicate control of current needed for demonic devices, such as transistors, to an extent impossible with full conductors such as metals. A semiconductor is made by adding elements - usually phosphorus or boron — to the silicon. if a small amount of the phosphorus is introduced as a gas while the silicon crystal is being formed into a chip, the phosphorus atoms bond together with some of the silicon atoms. Four electrons in the outer layers of each type of atom pair off, but one phosphorus electron is spare, so it is left free to form an electric current when a voltage is applied. Electrons are negatively charged, so this type of crystal is called an n- type (negative) semiconductor.

If small amount of boron is mixed with the silicon, there is one electron short in the bonding system, leaving a hole that attracts five electrons. Free holes create a positive charge so the crystal is called a p-type (positive) semiconductor. These two types of semiconductor are formed in sections within one crystal for most microchip components.

 

Picture Credit : Google

Within an area no bigger than a shirt button, a microchip holds as many as 450,000 electronic components. They are linked into electric circuits and are visible only under a microscope.

Microchips have transformed modern life and made some of the science fiction of the past into reality. They regulate digital watches, set programs on washing machines, and beat us at video games. They also manipulate robots on car-production lines and control national defence systems.

Electronically, the circuits that make up a microchip are not particularly complex —many are just switches. Their wizardry lies in their minute size, which allows signals to flow through at lightning speed. So they can carry out up to 250 million calculations in a second.

Most microchips are made of silicon, one of the most abundant elements on earth, and easily obtained from sand and rocks. A few are made from gallium arsenide — a compound of arsenic and the metal gallium, found in minerals such as coal.

 Chips for everything

There are various kinds of microchip. A microprocessor chip can be a computer in itself - in a washing machine, for example. Or it can be the nerve centre of a larger computer, controlling all its activities.

Memory chips store information in computers on sets of identical circuits —either permanently or temporarily. Interface chips translate the signals coming into the microprocessor from outside — such as from a keyboard — into binary code so that the electronic circuits can handle it. They also translate the outgoing signals back into figures or words for the computer screen.

Clock chips provide the timing needed for all the computer circuits to process electric signals in the right sequence. Each is linked to a quartz crystal that vibrates at a precise frequency.

 

Picture Credit : Google

In 1944, a child’s disappointment having to wait several days to see the photograph her father had taken led him to devise a quick method of film processing.

He was an American, Dr Edwin Land of Cambridge, Massachusetts, and in just a few months he had come up with a solution. Within three years the first instant-picture camera came on the market, capable of producing a finished black-and-white picture in about a minute. He called it the Polaroid-Land camera.

Today, a Polaroid camera can produce a black and white print in as little as ten seconds and a colour print in only a minute. The secret behind instant photography lies in the film, not in the camera. The film not only has a coating of light sensitive emulsion like a normal photographic film, but also carries the chemicals necessary to process it.

The film pack has both negative and positive sections – in a colour film each is many-layered, with dye developer layers alongside was colour-sensitive negative layer. The processing chemicals that trigger off the developing and printing process are in jelly-like form in a tiny plastic pod between the negative and positive sections.

The pod bursts when the film is removed from the camera through a pair of rollers. The chemicals are spread evenly over the film, and diffuse through it to set the picture processing in motion. The sandwich of film and print material develops in daylight outside the camera, and a positive picture is revealed when the negative and positive layers are pulled apart.

 

Picture Credit : Google

Two of the mist widely used cameras are the compact and the single-lens reflex (SLR). Both use 35mm film, although a few SLRs, including the Hassrlblad, use 120 film – 2¼ in (60 mm) wide – which needs less enlarging so gives better definition.

The two types differ in two main ways. First, most compacts have one built-in lens whereas the SLR can be fitted with a variety of interchangeable lenses. Secondly. The compact has a separate viewfinder whereas the SLR has a reflex viewfinder which ‘sees’ through the camera lens.

With a separate viewfinder, the photographer’s view does not coincide exactly with that of the lens (this is known as parallax error), so some compensation is needed for close-ups. With a reflex viewfinder, the photographer can see exactly the image that will be thrown onto the film, because light entering the camera lens is reflected by a mirror through a pentaprism (a five-sided prism)

 to the viewfinder eyepiece. The pentaprism reverses the mirror image and presents it to the eye the right way round. When the shutter release is pressed, the mirror springs upwards to let the light from the image onto the film.

The compact is smaller than the SLR, is easy to operate, and has few controls. The most expensive models have automatic focusing, automatic exposure, a zoom lens, built-in flash, and motor-driven film wind-on. They can take pictures comparable in quality to many SLRs.

SLR cameras can be programmed for auto-exposure in different ways – for example, a suitable aperture is automatically chosen for a manually selected shutter speed, or the other way round. Often the exposure meter has an indicator in the viewfinder to show the combination of aperture and shutter speed being set for optimum exposure.

The latest S;R models have built-in microprocessors controlling auto-focusing, auto-exposure and motor-driven wind-on. They can be fitted with a range of interchangeable backs offering different features, such as using different film and printing various information on the film.

 

Picture Credit : Google