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- A camera is an optical instrument used to capture an image. At their most basic, cameras are sealed boxes (the camera body) with a small hole (the aperture) that allow light in to capture an image on a light-sensitive surface (usually photographic film or a digital sensor). Cameras have various mechanisms to control how the light falls onto the light-sensitive surface. Lenses focus the light entering the camera, the size of the aperture can be widened or narrowed to let more or less light into the camera, and a shutter mechanism determines the amount of time the photo-sensitive surface is exposed to the light. The word camera comes from camera obscura, which means "dark chamber" and is the Latin name of the original device for projecting an image of external reality onto a flat surface. The modern photographic camera evolved from the camera obscura. The functioning of the camera is very similar to the functioning of the human eye. The first permanent photograph was made in 1825 by Joseph Nicéphore Niépce.

Camera History
- The forerunner to the photographic camera was the camera obscura. Camera obscura (Latin for "dark room") is the natural optical phenomenon that occurs when an image of a scene at the other side of a screen (or for instance a wall) is projected through a small hole in that screen and forms an inverted image (left to right and upside down) on a surface opposite to the opening. The oldest known record of this principle is a description by Han Chinese philosopher Mozi (ca. 470 to ca. 391 BC). Mozi correctly asserted that the camera obscura image is inverted because light travels in straight lines from its source. In the 11th century Arab physicist Ibn al-Haytham (Alhazen) wrote very influential books about optics, including experiments with light through a small opening in a darkened room. Ibn al-Haytham (c. 965–1040 AD), an Arab physicist also known as Alhazen, wrote very influential essays about the camera obscura, including experiments with light through a small opening in a darkened room.[2] The invention of the camera has been traced back to the work of Ibn al-Haytham,[3] who is credited with the invention of the pinhole camera.[4] While the effects of a single light passing through a pinhole had been described earlier,[3] Ibn al-Haytham gave the first correct analysis of the camera obscura,[5] including the first geometrical and quantitative descriptions of the phenomenon,[6] and was the first to use a screen in a dark room so that an image from one side of a hole in the surface could be projected onto a screen on the other side.[7] He also first understood the relationship between the focal point and the pinhole,[8] and performed early experiments with afterimage. Ibn al-Haytam's writings on optics became very influential in Europe through Latin translations, inspiring people such as Witelo, John Peckham, Roger Bacon, Leonardo Da Vinci, René Descartes and Johannes Kepler.[2] Camera obscuras were used as drawing aids since at least circa 1550. Since the late 17th century, portable camera obscura devices in tents and boxes were used as drawing aids. The first photographic camera developed for commercial manufacture was a daguerreotype camera, built by Alphonse Giroux in 1839. Giroux signed a contract with Daguerre and Isidore Niépce to produce the cameras in France,[9]:8–9 with each device and accessories costing 400 francs.[13]:38 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.[9][13]:39
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- A camera captures light photons, usually from the visible spectrum for human viewing, but in general could also be from other portions of the electromagnetic spectrum.[1]:vii All cameras use the same basic design: light enters an enclosed box through a converging or convex lens and an image is recorded on a light-sensitive medium (mainly a transition metal-halide). A shutter mechanism controls the length of time that light can enter the camera.[2]:1182–1183 Most cameras also have a viewfinder, which shows the scene to be recorded, and the ability to control focus and exposure so that it is not too bright or too dim.[3]:4
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- The aperture, sometimes called the diaphragm or iris,[4][5] is the opening through which light enters the camera.[6] Typically located in the lens,[7] this opening can be widened or narrowed to control the amount of light that strikes the film.[8] The aperture is controlled by the movements of overlapping plates or blades that rotate together and apart to shrink and expand the hole at the center.[8][9] The diameter of the aperture can be set manually, typically by adjusting a dial on the camera body or lens, or automatically based on calculations influenced by an internal light meter.[8] The size of the opening is set at standard increments, typically called "f-stops"[a][8] (but also "f-numbers", "stop numbers", or simply "steps" or "stops"), that usually range from f/1.4 to f/32 in standard increments: 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, and 32.[4] As the numbers increase, each increment (or "stop") halves the amount of light entering the camera.[7] Conversely, the lower the number, the larger the opening, and so the more light that is let into the camera.[8] The wider opening at the lower f-stops narrows the range of focus so the background of an image is blurry when focusing on the foreground, and vice versa. This "depth of field" increases as the aperture closes, so that objects that are at differing distances from the camera can both be in focus; when the aperture is at its narrowest, the foreground and background are both in sharp focus.[5]
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Shutter Speed
- The shutter, along with the aperture, is one of two ways to control the amount of light entering the camera. The shutter determines the duration that the light-sensitive surface is exposed to light. The shutter is opened, light enters the camera and exposes the film or sensor to light, and then the shutter closes.[7][10] There are two types of mechanical shutters. The leaf-type uses a circular iris diaphragm maintained under spring tension inside or just behind the lens that rapidly opens and closes when the shutter is released.[4] A focal-plane shutter. In this shutter, the metal shutter blades travel vertically. More commonly, a focal-plane shutter is used.[7] This shutter operates close to the film plane and employs metal plates or cloth curtains with an opening that passes across the light-sensitive surface. The curtains or plates have an opening that is pulled across the film plane during an exposure. The focal-plane shutter is typically used in single-lens reflex (SLR) cameras, since covering the film rather than blocking the light passing through the lens allows the photographer to view through the image 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).[8][4] Digital cameras may use one of these types of mechanical shutters or they may use an electronic shutter, the type used in the cameras of smartphones. Electronic shutters either record data from the entire sensor at the same time (a global shutter) or record the data line by line across the sensor (a rolling shutter).[8] In movie cameras, a rotary shutter opens and closes in sync with the advancing of each frame of film.[8][11] The duration is called the shutter speed or exposure time. The longer the shutter speed, the slower it is. Typical exposure times can range from one second to 1/1,000 of a second, though durations longer and shorter than this are not uncommon. In the early stages of photography, exposures were often several minutes long. These long exposure times often result in blurry images, as a single object is recorded in multiple places across a single image for the duration of the exposure. To prevent this, shorter exposure times can be used. Very short exposure times can capture fast-moving action and completely eliminate motion blur.[12][4][8][7] Like aperture settings, exposure times increment in powers of two. The two settings determine the exposure value (EV), a measure of how much light is recorded during the exposure. There is a direct relationship between the exposure times and aperture settings so that if the exposure time is lengthened one step, but the aperture opening is also narrowed one step, the amount of light exposing the film or sensor is the same.[7]
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- In most modern cameras, the amount of light entering the camera is measured using a built-in light meter or exposure meter.[b] Taken through the lens (and so called TTL metering), these readings are taken using a panel of semi-conductors that are sensitive to light.[9] They are used to help calculate the best exposure settings. These settings are typically determined automatically as the reading is used by the camera's microprocessor. The reading from the light meter is combined with aperture settings, exposure times, and film or sensor sensitivity to calculate the optimal exposure.[c] Light meters typically average the light in a scene to 18% middle gray. More advanced cameras are more nuanced in their metering, weighing the center of the frame more heavily (center-weighted metering), considering the differences in light across the image (matrix metering), or allowing the photographer to take a light reading at a specific point within the image (spot metering).[5][12][6][8]
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- The lens of a camera captures the light from the subject and brings it to a focus on the sensor. 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, and standard, medium telephoto. Lenses either have a fixed focal length (prime lens) or a variable focal length (zoom lens). 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 and documentary photography. The telephoto lens is useful for sports and wildlife but it is more susceptible to camera shake.[13]
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- 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.[14]
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Film speed
- Traditionally used to "tell the camera" the film speed of the selected film on film cameras, film speed numbers are employed on modern digital cameras as an indication of the system's gain from light to numerical output and to control the automatic exposure system. Film speed is usually measured via the ISO system. The higher the film speed number the greater the film sensitivity to light, whereas with a lower number, the film is less sensitive to light.
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White balance
- On digital cameras, electronic compensation for the color temperature associated with a given set of lighting conditions, ensuring that white light is registered as such on the imaging chip and therefore that the colors in the frame will appear natural. On mechanical, film-based cameras, this function is served by the operator's choice of film stock or with color correction filters. In addition to using white balance to register natural coloration of the image, photographers may employ white balance to aesthetic end, for example, white balancing to a blue object in order to obtain a warm color temperature.
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Camera accessories - Flash
- A flash, which provides a short burst of bright light during the exposure, is a commonly used artificial light source in photography. Most modern flash systems use a battery-powered high-voltage discharge through a gas-filled tube to generate bright light for a very short time (1/1,000 of a second or less).[d][6] Many flash units measure the light reflected from the flash to help determine the appropriate duration of the flash. When the flash is attached directly to the camera—typically in a slot at the top of the camera (the flash shoe or hot shoe) or through a cable—activating the shutter on the camera triggers the flash, and the camera's internal light meter can help determine the duration of the flash.[6][5]
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Other accessories
- Accessories for cameras are mainly for care, protection, special effects and functions. Lens hood: used on the end of a lens to block the sun or other light source to prevent glare and lens flare (see also matte box). Lens cap: covers and protects the lens during storage. Lens adapter: allows the use of lenses other than those for which the camera was designed. Lens filters: allow artificial colors or change light density. Lens extension tubes allow close focus in macro photography. Flash equipment: including light diffuser, mount and stand, reflector, soft box, trigger and cord. Care and protection: including camera case and cover, maintenance tools, and screen protector. Camera monitor: provides an off-camera view of the composition with a brighter and more colorful screen, and typically exposes more advanced tools such as framing guides, focus peaking, zebra stripes, waveform monitors (oftentimes as an "RGB parade"), vectorscopes and false color to highlight areas of the image critical to the photographer. Large format cameras use special equipment which includes magnifier loupe, view finder, angle finder, focusing rail /truck. Battery and sometimes a charger. Some professional SLR could be provided with interchangeable finders for eye-level or waist-level focusing, focusing screens, eye-cup, data backs, motor-drives for film transportation or external battery packs. Tripod, primarily used for keeping the camera steady while recording video, doing long exposure and timelapse photography. microscope adapter, an adapter used to connect a camera to a microscope to photograph what the microscope is examining. cable release, a remote shutter button that can be connected to the camera via a cable to remotely control the shutter, it can be used to lock the shutter open for a desired period of time. It is also commonly used to prevent camera shake from pressing the built in camera shutter button. Dew shield – Prevents moisture build up on the lens. UV filter, Can protect the front element of a lens from scratches, cracks, smudges, dirt, dust and moisture while keeping a minimum impact on image quality.
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