from The New Book of Knowledge®


When most people think of photography, they think of using a camera to "take a picture." People around the world will take over 10,000 pictures in the time it takes you to read this sentence, and several hundred million on this day alone. Photography is so much a part of daily life that we can forget how much it has changed the world.

The encyclopedia you are now reading would have been impossible without photography--and not just because of the photos used in the article. Books, magazines, and just about everything in print today--words as well as pictures--are printed by photographic processes. If you are reading this online, the same holds true. The microchips that make your computer work have their tiny circuits imprinted by a kind of photography.

Photography enables us to record our lives, as well as the events that shape history. It lets us see things we cannot normally see, freezing a baseball in midair or revealing tiny molecules that can be viewed only through a microscope. Special types of photography let physicians detect disease and injuries sooner and treat them better. Cameras carried by spacecraft have photographed all the planets, and some of these are now going beyond our solar system.

Skilled and imaginative photographers have made photography an art form. The beautiful pictures they take increase our appreciation and understanding of the world. Photographs documenting social problems and human suffering have moved people to take action and governments to change laws.

Today photography can be done almost in real time--people using digital cameras can see their pictures about as fast as they can take them. News photographers can instantly transmit photos from the scene of breaking news. A person sitting at a home computer can send a digital image halfway around the world in seconds.

How Photographs Are Made

The word "photography" comes from two Greek words meaning "writing" and "light," and photography is much like making a painting or drawing with light. To take a photograph, you need only three things: light, a camera, and a recording medium. For the first 150 years of photography, the recording medium was film--transparent plastic coated with crystals of a light-sensitive silver compound. In more and more cameras today, the recording medium is an electronic sensor or "imager" that converts the light that strikes it into digital information that can be stored in computer memory. Whether a camera uses film or a digital imager, though, the cameras are otherwise very similar.

When you take a picture, light reflected from your subject enters the camera through the lens, which focuses it on the film or on the digital imager. If you use film, the light rays form a latent (not visible) image of the subject on the film. The film has now been exposed, but to make the latent image visible, the film must be developed, or treated with chemicals. In digital recording, the focused light strikes a grid of tiny picture elements, or pixels. Each pixel records the brightness and color of the light that strikes it. Circuits in the camera then process the information into a bundle of organized information (an image file) that can later be read by a computer and reassembled into a picture.

Photographic Equipment

The camera and the recording medium are the basic tools of photography. Other important equipment includes interchangeable lenses, lights, flash units, and filters.

The Camera

All cameras, whether simple or complex, have five basic parts—the body, lens, shutter, film holder (in a digital camera, this is the imager), and viewfinder. More complex cameras may have special features as well.

The body of a camera is a lightproof framework, or box. It keeps out all light except what passes through the lens.

The lens—one or more pieces of glass or plastic with curved surfaces—is somewhat like a small magnifying glass. The lens concentrates the light entering the camera to make a sharp image of the photographed object on the film. All lenses must be focused so that the subject is as clear as possible.

The simplest cameras have a fixed-focus lens. This means the focus was set at one distance when the camera was made and cannot be changed. They are set to focus on objects beyond about 5 feet (1.5 meters).

With a more complex camera, the focus can be changed. Cameras that let you do this yourself--usually by turning a ring on the lens--are called manual-focus cameras. Those that change the focus automatically are called autofocus cameras. Some cameras are a combination of both.

The shutter is a mechanical device behind the lens that opens and closes to admit light. The photographer operates the shutter by pressing the shutter release, a button on the camera. In many cameras you can change the shutter speed. In dim light, a slower speed is preferable. This keeps the shutter open longer so that more light enters the camera. In bright sunlight, the shutter can be set at a faster speed, since there is plenty of light to produce an image on the film. A fast shutter speed lets you take pictures of subjects without blurring, even if they are moving.

When you press the shutter release on some digital cameras, the camera turns the digital imager on and off. This works much like the shutter on a film camera. Some digital cameras use mechanical shutters, however.

Very simple cameras have only one shutter speed. More complex and expensive cameras have many shutter speeds, ranging from 30 seconds to 1/8,000 of a second or even faster. Some cameras also have a setting that keeps the shutter open for long exposures.

Most cameras also have a diaphragm, which is used to make the aperture, or lens opening, larger or smaller to admit more or less light. Apertures are measured in f-numbers. The lower f-numbers, such as f/1.4 and f/2, are wide openings. These transmit more light to the film. The higher f-numbers, such as f/11 and f/16, are small lens openings. They transmit less light to the film.

The diaphragm also controls a photograph's depth of field. This is the amount of space in front of and behind the subject that is in focus. Higher f-stops increase the depth of field, and lower f-stops decrease it.

Film cameras include film holders to keep the film flat so that the image can be accurately focused. With small cameras, the film holder is built into the back of the camera. You load the film into the holder and close the camera. After taking a photograph, you advance the film so that the next blank spot on the roll (called a frame) is in place for the next picture. Most popular film cameras use cartridges of film that produce from 12 to 36 pictures and have frame counters to keep track of exposed pictures.

In digital cameras, the imager takes the place of the film holder. You do not have to load or advance film. But you will still have to store and keep track of the pictures you have taken, just as with a film camera. When you take a digital picture, the camera must move the image file to another place in the camera so you can take another picture. Some cameras have built-in memory, but that limits the number of pictures you can take—if you use all the memory, you have to either download the pictures to a computer or erase some of them. So most digital cameras instead store images on a memory card, which uses the same kind of memory chips a computer uses. These are about the size of postage stamps and are inserted into a side of the camera. The camera will indicate how many photos are stored on the card and how many more photos you can take before the card is filled up.

Every camera has a viewfinder—usually a small plastic or glass window—that shows the scene you are focusing on. Viewfinders in better cameras may also include lenses or reflecting prisms to provide a more accurate view of the picture being taken.

In a complex camera, the viewfinder may be combined with a device to aid in focusing. One older system is the rangefinder. This is a device on the camera that splits the image of the subject. When you look through the viewfinder, you see two images. To focus, you turn the focusing ring until the two images come together.

Another system that combines viewfinding and focusing is the reflex finder. In this, the image coming through the lens goes into an optical system that shows you the scene on a focusing screen. As you turn the focusing ring, you can see the image go in and out of focus, and you adjust the lens to make the image look sharp.

All but the simplest cameras include electronic circuits that measure the amount of light coming from the subject. In many cameras the proper exposure settings are shown in the viewfinder as the user adjusts the shutter speed and f-stop. This is called manual exposure setting. Some cameras set the exposure automatically, which is called autoexposure.

Film Cameras. Film cameras range from tiny pocket-sized units to very large cameras used primarily in professional studios.

The simplest cameras are called one-time-use cameras, or OTUC's. Also known as disposable cameras, these are the small cardboard and plastic cameras that are taken back to a store to get developed. An OTUC has a fixed-focus lens and a single exposure setting. You can get OTUC's with or without built-in flash. Some are designed for specific uses, such as taking black-and-white or underwater photography.

The point-and-shoot camera is more complex but is very popular because of its ease of use. It has an autofocus lens and different shutter speeds and lens openings that are set automatically, although some allow the user to make small changes in the exposure. This camera has a built-in flash that will fire when needed, unless it is turned off. It automatically loads the film, advances it to the next frame, and rewinds it when you finish the roll. Because you cannot change the lens, many point-and-shoot cameras have zoom lenses, which let you change the view from wide-angle to telephoto. Most point-and-shoot cameras use 35mm film, but some types use Advanced Photo System (APS) film, which comes in a small cartridge that is easier to load.

Instant cameras produce a fully developed print shortly after the picture is snapped. This is possible because the film includes the developing chemicals. After an image is exposed, the film comes in contact with the developers and is automatically processed. Instant cameras are less popular now that digital cameras allow pictures to be viewed right away.

Cameras that can be focused and use different lens openings and shutter speeds are called adjustable cameras. Most of these measure the light and indicate the correct lens opening and shutter speed or set them automatically. Today the most widely used adjustable camera is the single-lens reflex.

The single-lens reflex (SLR) is the most popular type of camera for serious photography, whether for film or digital capture. In the SLR camera, a mirror behind the lens reflects the image upward through a prism and onto a viewing screen. You can then see your picture and focus it. When you shoot the picture, the mirror automatically swings up out of the light path. The image strikes the film or imager as the shutter opens, and the exposure is made.

Most SLR's now use both autoexposure and autofocus, but better models also allow you to focus manually and make your own exposure settings. Many use interchangeable lenses, have built-in electronic flash, and take pictures on 35mm (millimeter) film.

Some SLR's use a type of roll film known as 120/220. This is larger than 35mm film, and the photos taken with it can show finer detail. These cameras are usually larger than 35mm SLR's, so they are often used with tripods. (A tripod is a three-legged stand that holds the camera steady and prevents blurring of the image.)

View cameras are another type of adjustable camera. They are most common in professional studios, but they are also used outdoors for photographing landscapes and architecture. They are much larger than SLR's and use individual sheets of film (usually 4 by 5 inches, but sometimes larger). They are used mostly by photographers who make pictures of products for advertising or other types of photography that require precise control of the image.

Many roll-film SLR's, as well as view cameras, have interchangeable film backs that can be switched with digital backs. This way, a photographer can shoot both film and digital versions of a subject.

Digital Cameras. Most digital cameras for amateurs are the point-and-shoot type. They focus automatically, set the lens opening and shutter speed automatically, and fire the flash when needed. Digital cameras have various other kinds of adjustments, but a digital point-and-shoot can set these automatically, too.

A digital point-and-shoot camera usually has an LCD monitor screen, which is like a small computer screen on the back of the camera. You can compose a picture using this screen—for this reason some digital cameras have no viewfinder—as well as view pictures you have already taken. Digital point-and-shoot cameras use memory cards to store pictures. The most popular are the Compact Flash (CF) and the Secure Digital (SD) types. Because digital pictures are electronic files, memory cards are not measured in frames but in megabytes, as in computer memory (1 megabyte equals about 1 million bytes). Memory cards come in sizes from 8 megabytes to 1 gigabyte (1 gigabyte equals 1,000 megabytes), and even larger ones are becoming available.

Most digital cameras for professional use are based on 35mm SLR's. These cameras use interchangeable lenses and allow a wide range of adjustments. They can take pictures that are sharper and clearer than digital point-and-shoot cameras and can often take pictures in a fast burst--several in less than a second. Digital SLR's are now widely used by news and nature photographers, among many others.

A new type of digital camera, the Electronic Viewfinder (EVF), works much like a SLR. However, the viewfinder eyepiece is really a tiny monitor. This eliminates the need for expensive and complex optical parts such as the mirror and prism.
Recording Media

Film. There are three main types of photographic film for general use: Black-and-white negative film for black-and-white photographs (usually prints), color negative film for color prints, and color reversal film (usually called color slide film) for color slides or transparencies.

All film has a plastic base thinly coated with crystals of a silver-bromide compound. The crystals are mixed in a transparent gelatin called an emulsion. Black-and-white film usually has just one layer of emulsion. Color film has three (or more) layers. Each is sensitive to, or records, one of the three primary colors of light--blue, green, and red.

When choosing general-use film, three factors must be considered--speed, graininess, and contrast. Film speed refers to a film's sensitivity to light, which can vary. Graininess is the degree of visibility of the silver crystals, or grains, in the photographic image. Graininess is especially noticeable when a photograph is enlarged. Contrast is the degree of difference between the light and dark areas of the subject. Generally, the faster the film, the grainier the photograph will be and the less contrast it will have. Photographs with too much contrast or too much grain lack fine detail.

Film speed is measured on a scale called the ISO film-speed index (for International Organization for Standards). Each film is given an ISO number that indicates its speed. Fast films have high numbers, and slow films have low numbers. The faster the film is, the more sensitive it is to light. Films for general purposes range from ISO 25 to ISO 3200. Films between ISO 200 and ISO 400 are the most commonly used all-purpose and outdoor films, but there are slower and faster special-purpose films.

Cameras that accept different kinds of film must be set to the proper film speed. Most do this automatically. With older cameras, however, you may have to set the film speed yourself by adjusting a dial at the top of the camera.

Digital Imagers. Digital cameras do not use film but a digital imager—either a charge-coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS). Both devices have a chip containing millions of tiny receptors (pixels) that record the color and intensity of the light falling on them. The more pixels an imager contains, the sharper and finer grained the resulting picture will be. (That is, it has a higher resolution.) Digital camera imagers are rated by the maximum number of pixels they can use. If a camera can take a picture made up of 1,600 by 1,200 pixels, for example, that means it has a resolution of 1,920,000 pixels (just multiply 1,600 by 1,200). This would be called a 1.9 megapixel camera. A 2,560 by 1,920 imager works out to 4,915,200 pixels, or about 4.9 megapixels.

A digital camera can take pictures at different quality levels, not just the highest available. For instance, a typical 3.2 megapixel camera can take pictures at the full 3.2 megapixels or at 2 megapixels, 1 megapixel, or at 640 by 480 pixels. What resolution should you use? A simple rule is to divide the resolution measurements by 200. This will tell you how big a print you can make, in inches, with full photographic quality. For example, if you take a picture at 1,600 by 1,200 pixels, you should be able to make an inkjet print of about 8 by 6 inches that looks as good as one you took with film. (Going a little bigger might give prints some grain and duller colors.) If you are just making a picture to e-mail, 640 by 480 is fine.

Another setting on digital cameras is compression. This is a method of squeezing the information in a digital file so it takes up less memory. This lets you put more pictures on a memory card. When the computer opens the picture, it uncompresses it, but some information may be lost. For the very best pictures, you should use as little compression as possible. But if you only want to e-mail pictures or make small prints, you can use more compression.


For SLR and view cameras, additional lenses are important accessories. These can be used to create images of different sizes and to take pictures of subjects that are far away or very close up.

Lenses come in a number of different focal lengths: normal, short, and long. With 35mm cameras, a normal-length lens—about 50mm—shows what the eye sees when looking at a scene.

Lenses with very short focal lengths are called wide-angle lenses. They take in a very large area but produce a small image of any object in a scene. One of the most interesting wide-angle lenses is the fish-eye lens. An 8mm fish-eye has a 180-degree angle (half circle) of view.

Telephoto lenses—those with long focal lengths—show less of the scene from a given spot. But they focus on a particular part of the scene and enlarge it, the way binoculars or telescopes do. Telephoto lenses are usually used for wildlife and sports photos.

Lenses with focal lengths that can be changed are called zoom lenses. You can get zoom lenses that stay in the telephoto range, such as 70-200mm, or zooms that stay in the wide-angle range, such as 17-28mm. The most popular zooms let you range from wide-angle to telephoto.

Lenses designed to focus very close up are called macro lenses. With these, you can photograph tiny details and small objects. You can also use simple, inexpensive lenses attached to the front of your normal or zoom lens to allow close focusing. These are called close-up lenses.

Lighting, Flashes, and Filters

How can you tell whether the light is bright enough to take a picture? You use an exposure meter. This measures the light and provides the proper exposure settings for the type of film you are using. Most cameras have exposure meters built into them. You can also buy a separate, handheld meter.

With an electronic flash, you can take pictures even when the other light is not bright enough. Most point-and-shoot cameras, and many OTUC's, have flash units built in. These automatically provide the correct exposure for subjects up to about 20 feet (6 meters) away.

Better cameras such as SLR's can use bigger add-on flash units. These are more powerful and provide more light. Some photographers use several flash units at once for a picture. They may also use continuous lighting (called hot lights), which are like powerful lightbulbs.

Filters are transparent pieces of glass or plastic that are placed over the lens. They change the light that hits the film. When used with black-and-white film, they change the tones of gray. When used with color film, they usually change the actual colors. In some cases, filters improve the light reaching the camera. For example, a polarizing filter gets rid of reflections, so that pictures can be taken through windows. Polarizers can also make a blue sky darker without altering other colors. Other filters are used for special effects, such as mist or soft focus.

Storing Images and Making Prints

When you finish a roll of film, the next step is developing and printing. If you take the film to the photofinishing counter in the supermarket or drugstore, it is usually sent to a large processing lab, especially if it is black-and-white or slide film. However, some places (minilabs) process color negative film at their own on-site labs, often within an hour.

Photofinishers can also make digital files from your negatives or slides and put them on a CD. This lets you view the images on a computer or television screen, then e-mail them, post them on your Web site, or use them for greeting cards, school reports, and other printed material. Photofinishers can also send these pictures to a Web site where your family and friends can view them.

If you take pictures with a digital camera, you can download them to a computer and see them almost immediately. To download, you can use a cable supplied with most cameras that connects the camera to the computer; a dock (a little cradle that holds the camera); or a card reader. The card reader is like a small disk drive that can read your camera's memory card. After downloading, you can look at the pictures on the screen and e-mail them.

If you want prints or enlargements of your digital pictures, you can bring your memory card to a photofinisher or you can make them yourself. Fairly inexpensive color inkjet printers can make very good color prints and enlargements.

Using software for desktop publishing, you can put your photos into greeting cards, calendars, and announcements. You may also want to enhance these photos with image-editing software. This process is often called the digital darkroom. (For more information, see the feature accompanying this article.)

Careers in Photography

At one time, most professional photographers were either self-taught or learned the trade as apprentices. Today, studying photography at a college or university is the best way to learn the profession. Those who just want to learn some of the basics—or perhaps concentrate on a specific topic in photography—can take individual courses in many colleges, universities, and some high schools. Taking one or two of these courses can also be a good way to decide if you want to pursue photography as a career.

Competition is strong for jobs in this field. Most professional photographers specialize in one or two kinds of pictures, such as advertising work, weddings and portraits, medical photography, nature photography, photomicrography, or photojournalism.

Stock photographers provide pictures to agencies, called stock agencies, which provide pictures to magazines and advertisers on a fee basis. The photographer usually shares a percentage of the fee. Stock photographers often specialize in specific areas.

History of Photography

A forerunner of the camera, the camera obscura, was invented hundreds of years before photography. It was actually a dark room with a tiny hole in one wall. Light came through the hole, producing an image on the opposite wall of the subject outside the hole.

For about 500 years, the camera obscura was used primarily for watching solar eclipses. Then artists and mapmakers realized it could be useful to them. As a result, portable versions were developed.

In time, the camera obscura was reduced to a small box much like a modern camera. A lens was placed in the hole where the light entered to help concentrate the light rays. There was also a diaphragm to control the amount of light coming in. The back of the box was a translucent screen. (Something translucent lets light pass through, but we cannot see detail through it.) A sheet of paper could be placed over the screen and the image traced on the paper. Artists such as Jan Vermeer used the camera obscura to make more realistic paintings.

In 1727, a German doctor, Johann Schulze, made the discovery that finally led to film. Schulze found that sunlight would blacken chalk that had been treated with a solution of silver nitrate. Modern photography is based on Schulze's discovery that light affects certain silver compounds.

The first successful photograph was made by a French inventor, Joseph Nicéphore Niepce, in 1826. He succeeded in capturing an image that did not immediately fade when light struck it. He placed the exposed metal plate (coated with an asphalt compound) in a solution that brought out the picture. The solution also washed away all the compound that had not yet been exposed to light. In other words, he fixed the picture. In 1829, Niepce became a partner of Louis Daguerre, a French theatrical designer. Before they had finished improving a developing process, Niepce died. Daguerre continued work on the process. In 1839, he revealed what became the first widely successful system of photography. His pictures were called daguerreotypes. Each was unique. There was no negative, and no prints could be made.

At about the same time, in England, William Henry Fox Talbot invented the first practical process that produced a negative from which prints could be made. This process, called calotype, began with a negative image on paper. It was then printed on another sensitized piece of paper to make a positive print.

Paper negatives had a drawback, however. The natural grain of the paper made the details of the picture somewhat unclear. To avoid this, people began experimenting with glass plates. Unfortunately, photographic chemicals would not stay on the glass. In 1847, Abel Niepce de Saint-Victor, the nephew of Joseph Niepce, tried something new. He coated a glass plate with albumen (the white of an egg). This sticky coating held the chemical fast.

In 1851, Frederick Scott Archer, an English chemist, introduced the wet collodion process. This process uses a syrupy, transparent liquid called collodion to hold the silver compounds on glass. The response of collodion plates to light was much faster than in other processes. But the photographer still had to coat the glass plate and load it into the camera. Then the plate had to be exposed, and the image developed, before the collodion dried. By the 1870's, gelatin-based dry emulsion began to replace the wet collodion plates.


In the 1880's, two developments changed photography. First, flexible, roll-up film was introduced by George Eastman, founder of the Eastman Kodak Company in Rochester, New York. A few years later, Eastman brought out a hand-held roll-film camera. This camera was easy to carry and use. Eastman's company even processed the film, so amateur photographers no longer had to do their own developing. This marked the beginning of photography's popularity as a hobby.

Along with its increasing popularity, photography began to be recognized as an art. Some photographers of the early 1900's experimented with new printing techniques to make their photographs look more like paintings. Later photographers produced abstract compositions through various darkroom techniques and multiple exposures. Others continued to use the shapes and textures of the natural world to create beautiful photographs.

In the 1920's and 1930's, more technical advances affected amateur and professional photographers alike. In 1924, the Leica camera was introduced in Germany. This miniature 35mm camera came with a wide range of accessories and attachments. The Leica gave photographers new flexibility, allowing them to take sharp, detailed pictures under many conditions. It was the forerunner of today's 35mm cameras. The range of photography was further extended with the development of convenient flash equipment in the late 1920's and early 1930's.

Many photographers used this new flexibility to dramatize social issues, such as poverty, with moving candid shots. This became known as documentary photography. Other photographers concentrated on recording news events. With advances in printing, newspapers and magazines were demanding more and more photographs for illustration.

Meanwhile, color photography had been developing since the early 1900's. In 1935, Kodachrome slide film was introduced. It became the first popular, affordable color film and is still used today. Early in the 1940's color-negative film appeared. This captured images on a negative, and so it could be readily printed on color printing paper. Color-negative film quickly became the most popular type of film in the world and remains so today.

Instant film, which develops within seconds, appeared in 1947. It was invented by the American scientist Edwin H. Land for use in his Polaroid Land Camera.

One of the most important developments in photography was the electronic flash, invented in the 1930's by Dr. Harold Edgerton of the Massachusetts Institute of Technology (MIT). This consisted of a burst of electricity shot through a tube to create a short but brilliant light. Unlike the single-use flash bulbs that had come before, a flash could be fired many times. It could also be made one-millionth of a second or shorter. This enabled photographers to freeze motion.

From the 1950's on, many of the advances in photography were for systems that automated various camera adjustments. In recent years remarkable improvements have been made in film, especially high-speed color-negative films.

History of Electronic Photography

Discoveries about electricity and magnetism in the early 1800's led to the invention of the electric telegraph. Inventors soon began seeking ways to transmit pictures over telegraph wires by electrical signals and to record them as electronic impulses, without the use of film or chemicals. The first facsimile (fax) machine was patented in 1843. By the end of the 1800's, facsimile machines that could send pictures were being developed, and in 1920 a photograph was transmitted across the Atlantic via the underwater telegraph cable. This was one of the first digital transmissions of phot