Functional Description-
A camera may work with the light of the visible spectrum or with other portions of the electromagnetic spectrum A still camera is an optical device which creates a single image of an object or scene, and records it on an electronic sensor or photographic film. All cameras use the same basic design: light enters an enclosed box through a converging lens and an image is recorded on a light-sensitive medium. A shutter mechanism controls the length of time that light can enter the camera. Most photographic cameras have functions that allow a person to view the scene to be recorded, allow for a desired part of the scene to be in focus, and to control the exposure so that it is not too bright or too dim. A data display, often a liquid crystal display (LCD), permits the user to view settings such as film speed, exposure, and shutter speed.
A film or video camera operates similarly to a still camera, except it records a series of static images in rapid succession, commonly at a rate of 24 frames per second. When the images are combined and displayed in order, the illusion of motion is achieved.
History-
The forerunner to the photographic camera was the camera obscura. In the fifth century B.C., the Chinese philosopher Mo Ti noted that a pinhole can form an inverted and focused image, when light passes through the hole and into a dark area. Mo Ti is the first recorded person to have exploited this phenomenon to trace the inverted image to create a picture. Writing in the fourth century B.C.,Aristotle also mentioned this principle. He described observing a partial solar eclipse in 330 B.C. by seeing the image of the Sun projected through the small spaces between the leaves of a tree. In the tenth century, the Arabic scholar Ibn al-Haytham (Alhazen) also wrote about observing a solar eclipse through a pinhole, and he described how a sharper image could be produced by making the opening of the pinhole smaller. English philosopher Roger Bacon wrote about these optical principles in his 1267 treatise Perspectiva. By the fifteenth century, artists and scientists were using this phenomenon to make observations. Originally, an observer had to enter an actual room, in which a pinhole was made on one wall. On the opposite wall, the observer would view the inverted image of the outside. The name camera obscura, Latin for "dark room", derives from this early implementation of the optical phenomenon. The term was first coined by mathematician and astronomer Johannes Kepler in his Ad Vitellionem paralipomena of 1604.
The Italian scientist Giambattista della Porta described the camera obscura in detail in his 1558 work Magia Naturalis, and specifically suggested that an artist could project a camera obscura's images onto paper, and trace the outlines. The camera obscura was popular as an aid for drawing and painting from the 1600s to the 1800s. Portable set-ups were devised in the 17th century. For example, Kepler had built a portable tent, and outfitted the camera obscura with a lens by 1620. This set-up remained popular up to the early 1800s. The scientist Robert Hooke presented a paper in 1694 to the Royal Society, in which he described a portable camera obscura. It was a cone-shaped box which fit onto the head and shoulders of its user. A hand-held device with a mirror reflex mechanism was first proposed by Johann Zahn in 1685, a design that would later be used in photographic cameras.
Before the development of the photographic camera, it had been known for hundreds of years that some substances, such as silver salts, darkened when exposed to sunlight. In a series of experiments, published in 1727, the German scientistJohann Heinrich Schulze demonstrated that the darkening of the salts was due to light alone, and not influenced by heat or exposure to air. The Swedish chemist Carl Wilhelm Scheele showed in 1777 that silver chloride was especially susceptible to darkening from light exposure, and that once darkened, it becomes insoluble in an ammonia solution. The first person to use this chemistry to create images was Thomas Wedgwood. To create images, Wedgwood placed items, such as leaves and insect wings, on ceramic pots coated with silver nitrate, and exposed the set-up to light. These images weren't permanent, however, as Wedgwood didn't employ a fixing mechanism. He ultimately failed at his goal of using the process to create fixed images created by a camera obscura.
The first permanent photograph of a camera image was made in 1826 by Joseph Nicephore Niepce using a sliding wooden box camera made by Charles and Vincent Chevalier in Paris. Niepce had been experimenting with ways to fix the images of a camera obscura since 1816. The photograph Niépce succeeded in creating shows the view from his window. It was made using an 8-hour exposure on pewter coated with bitumen. Niépce called his process "heliography". Niépce corresponded with the inventor Louis-Jacques-Mande Daguerre, and the pair entered into a partnership to improve the heliographic process. Niépce had experimented further with other chemicals, to improve contrast in his heliographs. Daguerre contributed an improved camera obscura design, but the partnership ended when Niépce died in 1833.Daguerre succeeded in developing a high-contrast and extremely sharp image by exposing on a plate coated with silver iodide, and exposing this plate again to mercury vapor. By 1837, he was able to fix the images with a common salt solution. He called this process Daguerreotypie, and tried unsuccessfully for a couple years to commercialize it. Eventually, with help of the scientist and politician François Arago, the French government acquired Daguerre's process for public release. In exchange, pensions were provided to Daguerre and Niépce's son, Isidore.
The first photographic camera developed for commercial manufacture was a daguerreotyp camera, built by Alphonse Giroux. Giroux signed a contract with Daguerre and Isidore Niépce to produce the cameras in France, which each device and accessories costing 400 francs. The camera was a double-box design, with a landscape lens fitted to the outer box, and a holder for a ground glass focusing screen and image plate on the inner box. By sliding the inner box, objects at various distances could be brought to as sharp a focus as desired. After a satisfactory image had been focused on the screen, the screen was replaced with a sensitized plate. A knurled wheel controlled a copper flap in front of the lens, which functioned as a shutter. The early daguerreotype cameras required long exposure times, which in 1839 could be from 5 to 30 minutes.
Similar cameras were used for exposing the silver-surfaced copper plates, commercially introduced in 1839, which were the first practical photographic medium. The collodion wet plate process that gradually replaced the daguerreotype during the 1850s required photographers to coat and sensitize thin glass or iron plates shortly before use and expose them in the camera while still wet. Early wet plate cameras were very simple and little different from Daguerreotype cameras, but more sophisticated designs eventually appeared. The Dubroni of 1864 allowed the sensitizing and developing of the plates to be carried out inside the camera itself rather than in a separate darkroom. Other cameras were fitted with multiple lenses for photographing several small portraits on a single larger plate, useful when making cartes de visite. It was during the wet plate era that the use of bellows for focusing became widespread, making the bulkier and less easily adjusted nested box design obsolete.
For many years, exposure times were long enough that the photographer simply removed the lens cap, counted off the number of seconds (or minutes) estimated to be required by the lighting conditions, then replaced the cap. As more sensitive photographic materials became available, cameras began to incorporate mechanical shutter mechanisms that allowed very short and accurately timed exposures to be made.
The first camera utilizing digital technologies to capture and store images was developed by Kodak engineer Steven Sasson in 1975. He used a charge-coupled device (CCD) provided by Fairchild Semiconductor, which provided only 0.1 megapixels to capture images. Sasson combined the CCD device with movie camera parts to create a digital camera that saved black and white images onto a cassette tape. The images were then read from the cassette and viewed on a TV monitor.
Image capture-
Traditional cameras capture light onto photographic film or photographic plate. Video and digital cameras use an electronic image sensor, usually a charge coupled device (CCD) or a CMOS sensor to capture images which can be transferred or stored in a memory card or other storage inside the camera for later playback or processing.
Cameras that capture many images in sequence are known as movie cameras or as ciné cameras in Europe; those designed for single images are still cameras.
However these categories overlap as still cameras are often used to capture moving images in special effects work and many modern cameras can quickly switch between still and motion recording modes.
A video camera is a category of movie camera that captures images electronically (either using analog or digital technology).
Lens-
The lens of a camera captures the light from the subject and brings it to a focus on the film or detector. The design and manufacture of the lens is critical to the quality of the photograph being taken. The technological revolution in camera design in the 19th century revolutionized optical glass manufacture and lens design with great benefits for modern lens manufacture in a wide range of optical instruments from reading glasses to microscopes. Pioneers included Zeiss and Leitz.
Camera lenses are made in a wide range of focal lengths. They range from extreme wide angle, wide angle, standard, medium telephoto and telephoto. Each lens is best suited to a certain type of photography. The extreme wide angle may be preferred for architecture because it has the capacity to capture a wide view of a building. The normal lens, because it often has a wide aperture, is often used for street anddocumentary photography. The telephoto lens is useful for sports and wildlife but it is more susceptible to camera shake.
Focus-
Due to the optical properties of photographic lenses, only objects within a limited range of distances from the camera will be reproduced clearly. The process of adjusting this range is known as changing the camera's focus. There are various ways of focusing a camera accurately. The simplest cameras have fixed focus and use a small aperture and wide-angle lens to ensure that everything within a certain range of distance from the lens, usually around 3 metres (10 ft) to infinity, is in reasonable focus. Fixed focus cameras are usually inexpensive types, such as single-use cameras. The camera can also have a limited focusing range or scale-focus that is indicated on the camera body. The user will guess or calculate the distance to the subject and adjust the focus accordingly. On some cameras this is indicated by symbols (head-and-shoulders; two people standing upright; one tree; mountains).
Rangefinder cameras allow the distance to objects to be measured by means of a coupled parallax unit on top of the camera, allowing the focus to be set with accuracy. Single-lens reflex cameras allow the photographer to determine the focus and composition visually using the objective lens and a moving mirror to project the image onto a ground glass or plastic micro-prism screen. Twin-lens reflex cameras use an objective lens and a focusing lens unit (usually identical to the objective lens.) in a parallel body for composition and focusing. View cameras use a ground glass screen which is removed and replaced by either a photographic plate or a reusable holder containing sheet film before exposure. Modern cameras often offer autofocus systems to focus the camera automatically by a variety of methods.
Some experimental cameras, for example the planar Fourier capture array (PFCA), do not require focusing to allow them to take pictures. In conventional digital photography, lenses or mirrors map all of the light originating from a single point of an in-focus object to a single point at the sensor plane. Each pixel thus relates an independent piece of information about the far-away scene. In contrast, a PFCA does not have a lens or mirror, but each pixel has an idiosyncratic pair of diffraction gratings above it, allowing each pixel to likewise relate an independent piece of information (specifically, one component of the 2D Fourier transform) about the far-away scene. Together, complete scene information is captured and images can be reconstructed by computation.
Some cameras have post focusing. Post focusing means take the pictures first and then focusing later at the personal computer. The camera uses many tiny lenses on the sensor to capture light from every camera angle of a scene and is called plenoptics technology. A current plenoptic camera design has 40,000 lenses working together to grab the optimal picture
The size of the aperture and the brightness of the scene controls the amount of light that enters the camera during a period of time, and the shutter controls the length of time that the light hits the recording surface. Equivalent exposures can be made with a larger aperture and a faster shutter speed or a corresponding smaller aperture and with the shutter speed slowed down.
Shutters-
Although a range of different shutter devices have been used during the development of the camera only two types have been widely used and remain in use today.
The Leaf shutter or more precisely the in-lens shutter is a shutter contained within the lens structure, often close to the diaphragm consisting of a number of metal leaves which are maintained under spring tension and which are opened and then closed when the shutter is released. The exposure time is determined by the interval between opening and closing. In this shutter design, the whole film frame is exposed at one time. This makes flash synchronisation much simpler as the flash only needs to fire once the shutter is fully open. Disadvantages of such shutters are their inability to reliably produce very fast shutter speeds ( faster than 1/500th second or so) and the additional cost and weight of having to include a shutter mechanism for every lens.
The focal-plane shutter operates as close to the film plane as possible and consists of cloth curtains that are pulled across the film plane with a carefully determined gap between the two curtains (typically running horizontally) or consisting of a series of metal plates (typically moving vertically) just in front of the film plane. The focal-plane shutter is primarily associated with the single lens reflex type of cameras, since covering the film rather than blocking light passing through the lens allows the photographer to view through the lens at all times except during the exposure itself. Covering the film also facilitates removing the lens from a loaded camera (many SLRs have interchangeable lenses).
Complexities-
Professional medium format SLR (single-lens-reflex) cameras (typically using 120/220 roll film) use a hybrid solution, since such a large focal-plane shutter would be difficult to make and/or may run slowly. A manually inserted blade known as a dark slide allows the film to be covered when changing lenses or film backs. A blind inside the camera covers the film prior to and after the exposure (but is not designed to be able to give accurately controlled exposure times) and a leaf shutter that is normally open is installed in the lens. To take a picture, the leaf shutter closes, the blind opens, the leaf shutter opens then closes again, and finally the blind closes and the leaf shutter re-opens (the last step may only occur when the shutter is re-cocked).
Using a focal-plane shutter, exposing the whole film plane can take much longer than the exposure time. The exposure time does not depend on the time taken to make the exposure over all, only on the difference between the time a specific point on the film is uncovered and then covered up again. For example an exposure of 1/1000 second may be achieved by the shutter curtains moving across the film plane in 1/50th of a second but with the two curtains only separated by 1/20th of the frame width. In fact in practice the curtains do not run at a constant speed as they would in an ideal design, obtaining an even exposure time depends mainly on being able to make the two curtains accelerate in a similar manner.
When photographing rapidly moving objects, the use of a focal-plane shutter can produce some unexpected effects, since the film closest to the start position of the curtains is exposed earlier than the film closest to the end position. Typically this can result in a moving object leaving a slanting image. The direction of the slant depends on the direction the shutter curtains run in (noting also that as in all cameras the image is inverted and reversed by the lens, i.e. "top-left" is at the bottom right of the sensor as seen by a photographer behind the camera).
Focal-plane shutters are also difficult to synchronise with flash bulbs and electronic flash and it is often only possible to use flash at shutter speeds where the curtain that opens to reveal the film completes its run and the film is fully uncovered, before the second curtain starts to travel and cover it up again. Typically 35mm film SLRs could sync flash at only up to 1/60th second if the camera has horizontal run cloth curtains, and 1/125th if using a vertical run metal shutter.
Film formats-
A wide range of film and plate formats have been used by cameras. In the early history plate sizes were often specific for the make and model of camera although there quickly developed some standardisation for the more popular cameras. The introduction of roll film drove the standardization process still further so that by the 1950s only a few standard roll films were in use. These included 120 film providing 8, 12 or 16 exposures, 220 film providing 16 or 24 exposures, 127 film providing 8 or 12 exposures (principally in Brownie cameras) and 135 (35 mm film) providing 12, 20 or 36 exposures – or up to 72 exposures in the half-frame format or in bulk cassettes for the Leica Camera range.
For cine cameras, film 35 mm wide and perforated with sprocket holes was established as the standard format in the 1890s. It is still used for nearly all film-based professional motion picture production. For amateur use, several smaller and therefore less expensive formats were introduced. 17.5 mm film, created by splitting 35 mm film, was one early amateur format, but 9.5 mm film, introduced in Europe in 1922, and 16 mm film, introduced in the US in 1923, soon became the standards for "home movies" in their respective hemispheres. In 1932, the even more economical 8 mm format was created by doubling the number of perforations in 16 mm film, then splitting it, usually after exposure and processing. The Super 8 format, still 8 mm wide but with smaller perforations to make room for substantially larger film frames, was introduced in 1965.
