A camera is a device that records images, either as a still photograph or as moving images known as videos or movies. The term comes from the camera obscura (Latin for "dark chamber"), an early mechanism of projecting images where an entire room functioned as a real-time imaging system; the modern camera evolved from the camera obscura. Cameras may work with the light of the visible spectrum or with other portions of the electromagnetic spectrum. A camera generally consists of an enclosed hollow with an opening (aperture) at one end for light to enter, and a recording or viewing surface for capturing the light at the other end. A majority of cameras have a lens positioned in front of the camera's opening to gather the incoming light and focus all or part of the image on the recording surface. The diameter of the aperture is often controlled by a diaphragm mechanism, but some cameras have a fixed-size aperture. A typical still camera takes one photo each time the user presses the shutter button. A typical movie camera continuously takes 24 film frames per second as long as the user holds down the shutter button. The forerunner to the camera was the camera obscura.[1] The camera obscura is an instrument consisting of a darkened chamber or box, into which light is admitted through a convex lens, forming an image of external objects on a surface of paper or glass, etc., placed at the focus of the lens.[2] The camera obscura was described by the Arabic scientist Ibn al-Haytham (Alhazen) in his Book of Optics(1015–1021).[3] Alhazen's work appeared in Latin translation as De Aspectibus ("Concerning vision") in about 1200, and the book influenced Roger Bacon's reflections on producing images using pinholes. The actual name of camera obscura was first applied to the technique by mathematician and astronomer Johannes Kepler in his Ad Vitellionem paralipomena of 1604; he would later improve the apparatus by adding a lens and making it transportable, in the form of a tent.[4][5] Irish scientist Robert Boyle and his assistant Robert Hooke later developed a portable camera obscura in the 1660s.[6] The first camera that was small and portable enough to be practical for photography was built by Johann Zahn in 1685, though it would be almost 150 years before technology caught up to the point where this was practical. Early photographic cameras were essentially similar to Zahn's model, though usually with the addition of sliding boxes for focusing. Before each exposure, a sensitized plate would be inserted in front of the viewing screen to record the image. Jacques Daguerre's popular daguerreotype process utilized copper plates, while the calotype process invented by William Fox Talbot recorded images on paper. The first permanent photograph was made in 1826 by Joseph Nicéphore Niépce using a sliding wooden box camera made by Charles and Vincent Chevalier in Paris. Niépce built on a discovery byJohann Heinrich Schultz (1724): a silver and chalk mixture darkens under exposure to light. However, while this was the birth of photography, the camera itself can be traced back much further. Before the invention of photography,there was no way to preserve the images produced by these cameras apart from manually tracing them. The development of the collodion wet plate process by Frederick Scott Archer in 1850 cut exposure times dramatically, but required photographers to prepare and develop their glass plates on the spot, usually in a mobile darkroom. Despite their complexity, the wet-plateambrotype and tintype processes were in widespread use in the latter half of the 19th century. Wet plate cameras were little different from previous designs, though there were some models, such as the sophisticated Dubroni of 1864, where the sensitizing and developing of the plates could be carried out inside the camera itself rather than in a separate darkroom. Other cameras were fitted with multiple lenses for making cartes de visite. It was during the wet plate era that the use of bellows for focusing became widespread. The first colour photograph was made by Scottish physicist James Clerk Maxwell, with the help of English inventor and photographer Thomas Sutton, in 1861[7] The electronic video camera tube was invented in the 1920s, starting a line of development that eventually resulted in digital cameras. Traditional cameras capture light onto photographic film or photographic plate. Video and digital cameras use electronics, usually acharge coupled device (CCD) or sometimes a CMOS sensor to capture images which can be transferred or stored in tape or computer memory 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 effectswork and modern digital cameras are often able to trivially switch between still and motion recording modes. A video camera is a category of movie camera that captures images electronically (either using analogue or digital technology). 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 18th 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. 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 camerasuse 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 e.g. by fishing.[8] 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. 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 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 or consisting of a series of metal plates moving either vertically or horizontally across the film plan. As the curtains or blades move at a constant speed, exposing the whole film plane can takes much longer than the exposure time. 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. When photographing rapidly moving objects, the use of a focal plane shutter can produce some unexpected effects. Focal plane shutters are also difficult to synchronise with electronic flash and it is often only possible to use flash at shutter speeds below 1/60th second although in some modern cameras that can be as fast as 1/100second/ The Copal 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. This disadvantage of such shutters is their inability to reliably produce very fast shutter speeds and the additional cost and weight of having to include a shutter mechanism for every lens. 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 standardisation 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 exposures , principally inBrownie 125 cameras and 35mm film providing 12, 20 or 36 exposures - or up to 72 exposures in bulk cassettes for the Leica Camera range. For cine cameras, 35mm film was the original film format but 16mm film soon followed produced by cutting 35mm in two. An early amateur format was 9.5mm. Later formats included 8mm film and Super 8. There are many accessories to a camera, those accessories are mainly for care, protection, special effects and functions. The earliest cameras produced in significant numbers used sensitised glass plates and are now termed plate cameras. Light entered a lens mounted on a lens board which was separated from the plate by an extendible bellows. Many of these cameras, had controls to raise or lower the lens and to tilt it forwards or backwards to control perspective . Focussing of these plate cameras was by the use of a ground glass screen at the point of focus. Because lens design only allowed rather small aperture lenses, the image on the ground glass screen was faint and most photographers had a dark cloth to cover their heads to allow focussing and composition to be carried out more easily. When focus and composition were satisfactory, the ground glass screen was removed and a sensitised plate put in its place protected by a dark slide (photography) . To make the exposure, the dark slide was carefully slid out and the shutter opened and then closed and the dark-slide replaced. In current designs the plate camera is best represented by the view camera. The large format camera is a direct successor of the early plate cameras and remain in use for high quality photography and for technical, architectural and industrial photography. There are three common types, the monorail camera, the field camera and the press camera. All use large format sheets of film, although there are backs for medium format 120-film available for most systems, and have an extensible bellows with the lens and shutter mounted on a lens plate at the front. These cameras have a wide range of movements allowing very close control of focus and perspective. The medium-format cameras has a film negative size somewhere in between the large format cameras and the smaller 35mm cameras. Typically these systems use 120- or 220-film. The most common sizes being 6x4.5 cm, 6x6 cm and 6x7 cm. The designs of this kind of camera shows greater variation than their larger brethren. Ranging from monorail systems, via the classic Hasselblad model with separate backs, to smaller rangefinder cameras. There are even compact amateur cameras available in this format. The introduction of films enabled the existing designs for plate cameras to be made much smaller and for the base-plate to be hinged so that it could be folded up compressing the bellows. These designs were very compact and small models were dubbed Vest pocket cameras. Box cameras were introduced as a budget level camera and had few if any controls. The original box Brownie models had a small reflex viewfinder mounted on the top of the camera and had no aperture or focussing controls and just a simple shutter. Later models such as the Brownie 127 had larger direct view optical viewfinders together with a curved film path to help As camera and lens technology developed and wide aperture lenses became more common range-finder cameras were introduced to make focussing more precise. The range finder had two separated viewfinder windows one of which was linked to the focusing mechanisms and moved right or left as the focussing ring was turned. The two separate images were brought together on a ground glass viewing screen. When vertical lines in the object being photographed met exactly in the combined image, the object was in focus. A normal composition viewfinder was also provided. In the single-lens reflex camera the photographer sees the scene through the camera lens. This avoids the problem of parallax which occurs when the viewfinder or viewing lens is separated from the taking lens. Single-lens reflex cameras have been made in several formats including 220/120 taking 8, 12 or 16 photographs on a 120 roll and twice that number of a 220 film. These correspond to 6x9, 6x6 and 6x4.5 respectively (all dimensions in cm). Notable manufacturers of large format SLR include Hasselblad, Mamiya,Bronica and Pentax. However the most common format of SLRs has been 35 mm and subsequently the migration to digital SLRs, using almost identical sized bodies and sometimes using the same lens systems. Almost all SLR used a front surfaced mirror in the optical path to direct the light from the lens via a viewing screen and pentaprism to the eyepiece. At the time of exposure the mirror flipped up out of the light path before the shutter opened. Some early cameras experimented other methods of providing through the lens viewing including the use of a semi transparent pellicle as in the Canon Pellix [12] and others with a small periscope such as in the Corfield Periflex series[13] Twin-lens reflex cameras used a pair of nearly identical lenses, one to form the image and one as a viewfinder. The lenses were arranged with the viewing lens immediately above the taking lens. The viewing lens projects an image onto a viewing screen which can be seen from above. Some manufacturers such as Mamiya also provided a reflex head to attach to the viewing screen to all the camera to be held to the eye when in use. The advantage of a TLR was that it could be easily focussed using the viewing screen and that under most circumstances the view seen in the viewing screen was identical to that recorded on film. At close distances however, parallax errors were encountered and some cameras also included an indicator to show what part of the composition would be excluded. Some TLR had interchangeable lenses but as these had to be paired lenses they were relatively heavy and did not provide the range of focal lengths that the SLR could support. Although most TLRs used 120 or 220 film some used 127 film. A ciné camera or movie camera is a type of photographic camera which takes a rapid sequence of photographs on strips of film. In contrast to a still camera, which captures a single snapshot at a time, the ciné camera takes a series of images, each called a "frame" through the use of an intermittent mechanism. The frames are later played back in a ciné projector at a specific speed, called the "frame rate" (number of frames per second). While viewing, a person's eyes and brain merge the separate pictures together to create the illusion of motion. The first ciné camera was built around 1888 and by 1890 several types were being manufactured. The standard film size for ciné cameras was quickly established as 35mm film and this remains in use to this day. Other professional standard formats include 70 mm film and 16mm film whilst amateurs film makers have used 9.5 mm film, 8mm film or Standard 8 and Super 8 before the move into digital format. The size and complexity of ciné cameras varies greatly depending on the uses required of the camera. Some professional equipment is very large and too heavy to be hand held whilst some amateur cameras were designed to be as small and light as possible enabling single-handed operation.History
[edit]Mechanics
[edit]Image capture
[edit]Lens
[edit]Focus
[edit]Exposure control
[edit]Shutters
[edit]Film formats
[edit]Camera accessories
[edit]Camera designs
[edit]Plate camera
[edit]Large format camera
[edit]Medium format camera
[edit]Folding camera
[edit]Box camera
[edit]Rangefinder camera
[edit]Single-lens reflex
[edit]Twin-lens reflex
[edit]Ciné camera
[edit]Image gallery
Camera
Tuesday, December 22, 2009
For other uses, see Camera (disambiguation).
Main article: History of the camera
Main article: Photographic lens
Main article: Photographic lens design
Main article: Shutter (photography)
Main article: Film formats
Main article: View camera
Main article: Medium-format
Main article: Rangefinder camera
Main article: Single-lens reflex camera
Main article: Twin-lens reflex camera
Main article: Movie camera
เขียนโดย Rueang ที่ 11:56 PM
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