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.