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Camera

A camera is an instrument used to capture and store images and videos, either digitally via an electronic image sensor, or chemically via a light-sensitive material such as photographic film. As a pivotal technology in the fields of photography and videography, cameras have played a significant role in the progression of visual arts, media, entertainment, surveillance, and scientific research. The invention of the camera dates back to the 19th century and has since evolved with advancements in technology, leading to a vast array of types and models in the 21st century.

Cameras function through a combination of multiple mechanical components and principles. These include exposure control, which regulates the amount of light reaching the sensor or film; the lens, which focuses the light; the viewfinder, which allows the user to preview the scene; and the film or sensor, which captures the image.

Several types of cameras exist, each suited to specific uses and offering unique capabilities. Single-lens reflex (SLR) cameras provide real-time, exact imaging through the lens. Large-format and medium-format cameras offer higher image resolution and are often used in professional and artistic photography. Compact cameras, known for their portability and simplicity, are popular in consumer photography. Rangefinder cameras, with separate viewing and imaging systems, were historically widely used in photojournalism. Motion picture cameras are specialized for filming cinematic content, while digital cameras, which became prevalent in the late 20th and early 21st century, use electronic sensors to capture and store images.

The rapid development of smartphone camera technology in the 21st century has blurred the lines between dedicated cameras and multifunctional devices, profoundly influencing how society creates, shares, and consumes visual content.

19th century
Beginning with the use of the camera obscura and transitioning to complex photographic cameras, the evolution of the technology in the 19th century was driven by pioneers like Thomas Wedgwood, Nicéphore Niépce, and Henry Fox Talbot. First using the camera obscura for chemical experiments, they ultimately created cameras specifically for chemical photography, and later reduced the camera's size and optimized lens configurations.

The introduction of the daguerreotype process in 1839 facilitated commercial camera manufacturing, with various producers contributing diverse designs. As camera manufacturing became a specialized trade in the 1850s, designs and sizes were standardized.

The latter half of the century witnessed the advent of dry plates and roll-film, prompting a shift towards smaller and more cost-effective cameras, epitomized by the original Kodak camera, first produced in 1888. This period also saw significant advancements in lens technology and the emergence of color photography, leading to a surge in camera ownership.

20th century
The first half of the 20th century saw continued miniaturization and the integration of new manufacturing materials. After World War I, Germany took the lead in camera development, spearheading industry consolidation and producing precision-made cameras. The industry saw significant product launches such as the Leica camera and the Contax, which were enabled by advancements in film and lens designs. Additionally, there was a marked increase in accessibility to cinematography for amateurs with Eastman Kodak's production of the first 16-mm and 8-mm reversal safety films. The World War II era saw a focus on the development of specialized aerial reconnaissance and instrument-recording equipment, even as the overall pace of non-military camera innovation slowed.

In the second half of the century, Japanese manufacturers in particular advanced camera technology. From the introduction of the affordable Ricohflex III TLR in 1952 to the first 35mm SLR with automatic exposure, the Olympus AutoEye in 1960, new designs and features continuously emerged. Electronics became integral to camera design in the 1970s, evident in models like Polaroid's SX-70 and Canon's AE-1.

Transition to digital photography marked the late 20th century, culminating in digital camera sales surpassing film cameras in the United States by 2003. In contrast, the film camera industry in the UK, Western Europe, and the USA declined during this period, while manufacturing continued in the USSR, German Democratic Republic, and China, often mimicking Western designs.

21st century
The 21st century witnessed the mass adoption of digital cameras and significant improvements in sensor technology. A major revolution came with the incorporation of cameras into smartphones, making photography a commonplace activity. The century also marked the rise of computational photography, using algorithms and AI to enhance image quality. Features like low-light and HDR photography, optical image stabilization, and depth-sensing became common in smartphone cameras.

Mechanics
Most cameras capture light from the visible spectrum, while specialized cameras capture other portions of the electromagnetic spectrum, such as infrared.

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. A shutter mechanism controls the length of time that light enters the camera.

Most cameras also have a viewfinder, which shows the scene to be recorded, along with means to adjust various combinations of focus, aperture and shutter speed.

Aperture

Light enters the camera through an aperture, an opening adjusted by overlapping plates called the aperture ring. Typically located in the lens, this opening can be widened or narrowed to alter the amount of light that strikes the film or sensor. The size of the aperture can be set manually, by rotating the lens or adjusting a dial or automatically based on readings from an internal light meter.

As the aperture is adjusted, the opening expands and contracts in increments called f-stops. The smaller the f-stop, the more light is allowed to enter the lens, increasing the exposure. Typically, f-stops range from 1.4 to 32 in standard increments: 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, and 32. The light entering the camera is halved with each increasing increment.

The wider opening at lower f-stops narrows the range of focus so the background is blurry while the foreground is in focus. This depth of field increases as the aperture closes. A narrow aperture results in a high depth of field, meaning that objects at many different distances from the camera will appear to be in focus. What is acceptably in focus is determined by the circle of confusion, the photographic technique, the equipment in use and the degree of magnification expected of the final image.

Shutter
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 opens, light enters the camera and exposes the film or sensor to light, and then the shutter closes.

There are two types of mechanical shutters: the leaf-type shutter and the focal-plane shutter. 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. More commonly, a focal-plane shutter is used. 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 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 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, as many SLRs have interchangeable lenses.

A digital camera may use a mechanical or electronic shutter, the latter of which is common in smartphone cameras. Electronic shutters either record data from the entire sensor simultaneously (a global shutter) or record the data line by line across the sensor (a rolling shutter). In movie cameras, a rotary shutter opens and closes in sync with the advancement of each frame of film.

The duration for which the shutter is open is called the shutter speed or exposure time. Typical exposure times can range from one second to 1/1,000 of a second, though longer and shorter durations are not uncommon. In the early stages of photography, exposures were often several minutes long. These long exposure times often resulted 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 eliminate motion blur. However, shorter exposure times require more light to produce a properly exposed image, so shortening the exposure time is not always possible.

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, then the amount of light that contacts the film or sensor is the same.

Light meter
In most modern cameras, the amount of light entering the camera is measured using a built-in light meter or exposure meter. Taken through the lens (called TTL metering), these readings are taken using a panel of light-sensitive semiconductors. They are used to calculate optimal 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 incorporated with aperture settings, exposure times, and film or sensor sensitivity to calculate the optimal exposure.

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).

Lens
A camera lens is an assembly of multiple optical elements, typically made from high-quality glass. Its primary function is to focus light onto a camera's film or digital sensor, thereby producing an image. This process significantly influences image quality, the overall appearance of the photo, and which parts of the scene are brought into focus.

A camera lens is constructed from a series of lens elements, small pieces of glass arranged to form an image accurately on the light-sensitive surface. Each element is designed to reduce optical aberrations, or distortions, such as chromatic aberration (a failure of the lens to focus all colors at the same point), vignetting (darkening of image corners), and distortion (bending or warping of the image). The degree of these distortions can vary depending on the subject of the photo.

The focal length of the lens, measured in millimeters, plays a critical role as it determines how much of the scene the camera can capture and how large the objects appear. Wide-angle lenses provide a broad view of the scene, while telephoto lenses capture a narrower view but magnify the objects. The focal length also influences the ease of taking clear pictures handheld, with longer lengths making it more challenging to avoid blur from small camera movements.

Two primary types of lenses include zoom and prime lenses. A zoom lens allows for changing its focal length within a certain range, providing the convenience of adjusting the scene capture without moving the camera or changing the lens. A prime lens, in contrast, has a fixed focal length. While less flexible, prime lenses often provide superior image quality, are typically lighter, and perform better in low light.

Focus involves adjusting the lens elements to sharpen the image of the subject at various distances. The focus is adjusted through the focus ring on the lens, which moves the lens elements closer or further from the sensor. Autofocus is a feature included in many lenses, which uses a motor within the lens to adjust the focus quickly and precisely based on the lens's detection of contrast or phase differences. This feature can be enabled or disabled using switches on the lens body.

Advanced lenses may include mechanical image stabilization systems that move lens elements or the image sensor itself to counteract camera shake, especially beneficial in low-light conditions or at slow shutter speeds. Lens hoods, filters, and caps are accessories used alongside a lens to enhance image quality, protect the lens, or achieve specific effects.

Viewfinder
The camera's viewfinder provides a real-time approximation of what will be captured by the sensor or film. It assists photographers in aligning, focusing, and adjusting the composition, lighting, and exposure of their shots, enhancing the accuracy of the final image.

Viewfinders fall into two primary categories: optical and electronic. Optical viewfinders, commonly found in Single-Lens Reflex (SLR) cameras, use a system of mirrors or prisms to reflect light from the lens to the viewfinder, providing a clear, real-time view of the scene. Electronic viewfinders, typical in mirrorless cameras, project an electronic image onto a small display, offering a wider range of information such as live exposure previews and histograms, albeit at the cost of potential lag and higher battery consumption. Specialized viewfinder systems exist for specific applications, like subminiature cameras for spying or underwater photography.

Parallax error, resulting from misalignment between the viewfinder and lens axes, can cause inaccurate representations of the subject's position. While negligible with distant subjects, this error becomes prominent with closer ones. Some viewfinders incorporate parallax-compensating devices to mitigate that issue.

Film and sensor
Image capture in a camera occurs when light strikes a light-sensitive surface: photographic film or a digital sensor. Housed within the camera body, the film or sensor records the light's pattern when the shutter is briefly opened to allow light to pass during the exposure.

Loading film into a film camera is a manual process. The film, typically housed in a cartridge, is loaded into a designated slot in the camera. One end of the film strip, the film leader, is manually threaded onto a take-up spool. Once the back of the camera is closed, the film advance lever or knob is used to ensure the film is correctly placed. The photographer then winds the film, either manually or automatically depending on the camera, to position a blank portion of the film in the path of the light. Each time a photo is taken, the film advance mechanism moves the exposed film out of the way, bringing a new, unexposed section of film into position for the next shot.

The film must be advanced after each shot to prevent double exposure — where the same section of film is exposed to light twice, resulting in overlapped images. Once all frames on the film roll have been exposed, the film is rewound back into the cartridge, ready to be removed from the camera for developing.

In digital cameras, sensors typically comprise Charge-Coupled Devices (CCDs) or Complementary Metal-Oxide-Semiconductor (CMOS) chips, both of which convert incoming light into electrical charges to form digital images. CCD sensors, though power-intensive, are recognized for their excellent light sensitivity and image quality. Conversely, CMOS sensors offer individual pixel readouts, leading to less power consumption and faster frame rates, with their image quality having improved significantly over time.

Digital cameras convert light into electronic data that can be directly processed and stored. The volume of data generated is dictated by the sensor's size and properties, necessitating storage media such as Compact Flash, Memory Sticks, and SD (Secure Digital) cards. Modern digital cameras typically feature a built-in monitor for immediate image review and adjustments. Digital images are also more readily handled and manipulated by computers, offering a significant advantage in terms of flexibility and post-processing potential over traditional film.

Flash
A flash provides a short burst of bright light during exposure and 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).

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.

Additional flash equipment can include a light diffuser, mount and stand, reflector, soft box, trigger and cord.

Other accessories
Accessories for cameras are mainly used for care, protection, special effects, and functions. Large format cameras use special equipment that includes a magnifier loupe, view finder, angle finder, and focusing rail/truck. Some professional SLRs can be provided with interchangeable finders for eye-level or waist-level focusing, focusing screens, eyecup, data backs, motor-drives for film transportation or external battery packs.
 * 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 camera lens when not in use.
 * Lens adapter: allows the use of lenses other than those for which the camera was designed.
 * Filter: allows artificial colors or changes light density.
 * Lens extension tube: allows close focus in macro photography.
 * 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.
 * Tripod: primarily used for keeping the camera steady while recording video, doing a long exposure, and time-lapse photography.
 * Microscope adapter: used to connect a camera to a microscope to photograph what the microscope is examining.
 * Cable release: used to remotely control the shutter using a remote shutter button that can be connected to the camera via a cable. It can be used to lock the shutter open for the desired period, and it is also commonly used to prevent the 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.
 * Battery and sometimes a charger.

Single-lens reflex (SLR) camera
In photography, the single-lens reflex camera (SLR) is provided with a mirror to redirect light from the lens to the viewfinder prior to releasing the shutter for composing and focusing an image. When the shutter is released, the mirror swings up and away, allowing the exposure of the photographic medium, and instantly returns after the exposure is finished. No SLR camera before 1954 had this feature, although the mirror on some early SLR cameras was entirely operated by the force exerted on the shutter release and only returned when the finger pressure was released. The Asahiflex II, released by Japanese company Asahi (Pentax) in 1954, was the world's first SLR camera with an instant return mirror.

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 sheet film 5x7" and 4x5", roll film 220/120 taking 8,10, 12, or 16 photographs on a 120 roll, and twice that number of a 220 film. These correspond to 6x9, 6x7, 6x6, and 6x4.5 respectively (all dimensions in cm). Notable manufacturers of large format and roll film SLR cameras include Bronica, Graflex, Hasselblad, Seagull, Mamiya and Pentax. However, the most common format of SLR cameras has been 35 mm and subsequently the migration to digital SLR cameras, using almost identical sized bodies and sometimes using the same lens systems.

Almost all SLR cameras use 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 is flipped up out of the light path before the shutter opens. Some early cameras experimented with other methods of providing through-the-lens viewing, including the use of a semi-transparent pellicle as in the Canon Pellix and others with a small periscope such as in the Corfield Periflex series.

Large-format camera
The large-format camera, taking sheet film, is a direct successor of the early plate cameras and remained in use for high-quality photography and technical, architectural, and industrial photography. There are three common types: the view camera, with its monorail and field camera variants, and the press camera. They have extensible bellows with the lens and shutter mounted on a lens plate at the front. Backs taking roll film and later digital backs are available in addition to the standard dark slide back. These cameras have a wide range of movements allowing very close control of focus and perspective. Composition and focusing are done on view cameras by viewing a ground-glass screen which is replaced by the film to make the exposure; they are suitable for static subjects only and are slow to use.

Plate camera

The earliest cameras produced in significant numbers were plate cameras, using sensitized glass plates. Light entered a lens mounted on a lens board which was separated from the plate by extendible bellows. There were simple box cameras for glass plates but also single-lens reflex cameras with interchangeable lenses and even for color photography (Autochrome Lumière). Many of these cameras had controls to raise, lower, and tilt the lens forwards or backward to control perspective.

Focusing 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 focusing and composition to be carried out more quickly. When focus and composition were satisfactory, the ground glass screen was removed, and a sensitized plate was put in its place protected by a dark slide. To make the exposure, the dark decline was carefully slid out and the shutter opened, and then closed and the dark fall replaced.

Glass plates were later replaced by sheet film in a dark slide for sheet film; adapter sleeves were made to allow sheet film to be used in plate holders. In addition to the ground glass, a simple optical viewfinder was often fitted.

Medium-format camera
Medium-format cameras have a film size between the large-format cameras and smaller 35 mm cameras. Typically these systems use 120 or 220 roll film. The most common image sizes are 6×4.5 cm, 6×6 cm and 6×7 cm; the older 6×9 cm is rarely used. The designs of this kind of camera show greater variation than their larger brethren, ranging from monorail systems through the classic Hasselblad model with separate backs, to smaller rangefinder cameras. There are even compact amateur cameras available in this format.

Twin-lens reflex camera

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 allow the camera to be held to the eye when in use. The advantage of a TLR was that it could be easily focused using the viewing screen and that under most circumstances the view seen on 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 TLRs 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. Most TLRs used 120 or 220 films; some used the smaller 127 films.

Instant camera
After exposure, every photograph is taken through pinch rollers inside the instant camera. Thereby the developer paste contained in the paper 'sandwich' is distributed on the image. After a minute, the cover sheet just needs to be removed and one gets a single original positive image with a fixed format. With some systems, it was also possible to create an instant image negative, from which then could be made copies in the photo lab. The ultimate development was the SX-70 system of Polaroid, in which a row of ten shots – engine driven – could be made without having to remove any cover sheets from the picture. There were instant cameras for a variety of formats, as well as adapters for instant film use in medium- and large-format cameras.

Subminiature camera

Subminiature cameras were first produced in the twentieth century and use film significantly smaller than 35mm. The expensive 8×11mm Minox, the only type of camera produced by the company from 1937 to 1976, became very widely known and was often used for espionage (the Minox company later also produced larger cameras). Later inexpensive subminiatures were made for general use, some using rewound 16 mm cine film. Image quality with these small film sizes was limited.

Folding camera
The introduction of films enabled the existing designs for plate cameras to be made much smaller and for the baseplate 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. Folding roll film cameras were preceded by folding plate cameras, more compact than other designs.

Box camera

Box cameras were introduced as budget-level cameras 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 focusing 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 reduce the impact of deficiencies in the lens.

Rangefinder camera

As camera lens technology developed and wide aperture lenses became more common, rangefinder cameras were introduced to make focusing more precise. Early rangefinders had two separate viewfinder windows, one of which is linked to the focusing mechanisms and moved right or left as the focusing ring is turned. The two separate images are brought together on a ground glass viewing screen. When vertical lines in the object being photographed meet exactly in the combined image, the object is in focus. A normal composition viewfinder is also provided. Later the viewfinder and rangefinder were combined. Many rangefinder cameras had interchangeable lenses, each lens requiring its range- and viewfinder linkages.

Rangefinder cameras were produced in half- and full-frame 35 mm and roll film (medium format).

Motion picture cameras
A movie camera or a 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.

Cameras that capture many images in sequence are known as movie cameras or as cine 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 ciné camera or movie camera takes a rapid sequence of photographs on an image sensor or 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 visual system merge the separate pictures 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 remained in use until the transition to digital cinematography. Other professional standard formats include 70 mm film and 16 mm film whilst amateur filmmakers used 9.5 mm film, 8 mm film, or Standard 8 and Super 8 before the move into digital format.

The size and complexity of ciné cameras vary greatly depending on the uses required of the camera. Some professional equipment is very large and too heavy to be handheld whilst some amateur cameras were designed to be very small and light for single-handed operation.

Professional video camera

A professional video camera (often called a television camera even though the use has spread beyond television) is a high-end device for creating electronic moving images (as opposed to a movie camera, that earlier recorded the images on film). Originally developed for use in television studios, they are now also used for music videos, direct-to-video movies, corporate and educational videos, marriage videos, etc.

These cameras earlier used vacuum tubes and later electronic image sensors.

Camcorders

A camcorder is an electronic device combining a video camera and a video recorder. Although marketing materials may use the colloquial term "camcorder", the name on the package and manual is often "video camera recorder". Most devices capable of recording video are camera phones and digital cameras primarily intended for still pictures; the term "camcorder" is used to describe a portable, self-contained device, with video capture and recording its primary function.

Digital camera

A digital camera (or digicam) is a camera that encodes digital images and videos and stores them for later reproduction. They typically use semiconductor image sensors. Most cameras sold today are digital, and they are incorporated into many devices ranging from mobile phones (called camera phones) to vehicles.

Digital and film cameras share an optical system, typically using a lens of variable aperture to focus light onto an image pickup device. The aperture and shutter admit the correct amount of light to the imager, just as with film but the image pickup device is electronic rather than chemical. However, unlike film cameras, digital cameras can display images on a screen immediately after being captured or recorded, and store and delete images from memory. Most digital cameras can also record moving videos with sound. Some digital cameras can crop and stitch pictures & perform other elementary image editing.

Consumers adopted digital cameras in the 1990s. Professional video cameras transitioned to digital around the 2000s–2010s. Finally, movie cameras transitioned to digital in the 2010s.

The first camera using digital electronics 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 0.01 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. Later, cassette tapes were replaced by flash memory.

In 1986, Japanese company Nikon introduced an analog-recording electronic single-lens reflex camera, the Nikon SVC. The first full-frame digital SLR cameras were developed in Japan from around 2000 to 2002: the MZ-D by Pentax, the N Digital by Contax's Japanese R6D team, and the EOS-1Ds by Canon. Gradually in the 2000s, the full-frame DSLR became the dominant camera type for professional photography.

On most digital cameras a display, often a liquid crystal display (LCD), permits the user to view the scene to be recorded and settings such as ISO speed, exposure, and shutter speed.

Camera phone

In 2000, Sharp introduced the world's first digital camera phone, the J-SH04 J-Phone, in Japan. By the mid-2000s, higher-end cell phones had an integrated digital camera, and by the beginning of the 2010s, almost all smartphones had an integrated digital camera.

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Acetylcholine

Acetylcholine (ACh) is an organic compound that functions in the brain and body of many types of animals (including humans) as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Parts in the body that use or are affected by acetylcholine are referred to as cholinergic.

Acetylcholine is the neurotransmitter used at the neuromuscular junction—in other words, it is the chemical that motor neurons of the nervous system release in order to activate muscles. This property means that drugs that affect cholinergic systems can have very dangerous effects ranging from paralysis to convulsions. Acetylcholine is also a neurotransmitter in the autonomic nervous system, both as an internal transmitter for the sympathetic nervous system and as the final product released by the parasympathetic nervous system. Acetylcholine is the primary neurotransmitter of the parasympathetic nervous system.

In the brain, acetylcholine functions as a neurotransmitter and as a neuromodulator. The brain contains a number of cholinergic areas, each with distinct functions; such as playing an important role in arousal, attention, memory and motivation.

Acetylcholine has also been found in cells of non-neural origins as well as microbes. Recently, enzymes related to its synthesis, degradation and cellular uptake have been traced back to early origins of unicellular eukaryotes. The protist pathogen Acanthamoeba spp. have shown evidence of the presence of ACh, which provides growth and proliferative signals via a membrane located M1-muscarinic receptor homolog.

Partly because of its muscle-activating function, but also because of its functions in the autonomic nervous system and brain, many important drugs exert their effects by altering cholinergic transmission. Numerous venoms and toxins produced by plants, animals, and bacteria, as well as chemical nerve agents such as Sarin, cause harm by inactivating or hyperactivating muscles through their influences on the neuromuscular junction. Drugs that act on muscarinic acetylcholine receptors, such as atropine, can be poisonous in large quantities, but in smaller doses they are commonly used to treat certain heart conditions and eye problems. Scopolamine, or Diphenhydramine, which also act mainly on muscarinic receptors in an inhibitory fashion in the brain (especially the M1 receptor) can cause delirium, hallucinations, and amnesia through receptor antagonism at these sites. So far as of 2016, only the M1 receptor subtype has been implicated in anticholinergic delirium. The addictive qualities of nicotine are derived from its effects on nicotinic acetylcholine receptors in the brain.

Chemistry
Acetylcholine is a choline molecule that has been acetylated at the oxygen atom. Because of the charged ammonium group, acetylcholine does not penetrate lipid membranes. Because of this, when the molecule is introduced externally, it remains in the extracellular space and at present it is considered that the molecule does not pass through the blood–brain barrier.

Biochemistry
Acetylcholine is synthesized in certain neurons by the enzyme choline acetyltransferase from the compounds choline and acetyl-CoA. Cholinergic neurons are capable of producing ACh. An example of a central cholinergic area is the nucleus basalis of Meynert in the basal forebrain. The enzyme acetylcholinesterase converts acetylcholine into the inactive metabolites choline and acetate. This enzyme is abundant in the synaptic cleft, and its role in rapidly clearing free acetylcholine from the synapse is essential for proper muscle function. Certain neurotoxins work by inhibiting acetylcholinesterase, thus leading to excess acetylcholine at the neuromuscular junction, causing paralysis of the muscles needed for breathing and stopping the beating of the heart.

Functions

Acetylcholine functions in both the central nervous system (CNS) and the peripheral nervous system (PNS). In the CNS, cholinergic projections from the basal forebrain to the cerebral cortex and hippocampus support the cognitive functions of those target areas. In the PNS, acetylcholine activates muscles and is a major neurotransmitter in the autonomic nervous system.

Cellular effects
Like many other biologically active substances, acetylcholine exerts its effects by binding to and activating receptors located on the surface of cells. There are two main classes of acetylcholine receptor, nicotinic and muscarinic. They are named for chemicals that can selectively activate each type of receptor without activating the other: muscarine is a compound found in the mushroom Amanita muscaria; nicotine is found in tobacco.

Nicotinic acetylcholine receptors are ligand-gated ion channels permeable to sodium, potassium, and calcium ions. In other words, they are ion channels embedded in cell membranes, capable of switching from a closed to an open state when acetylcholine binds to them; in the open state they allow ions to pass through. Nicotinic receptors come in two main types, known as muscle-type and neuronal-type. The muscle-type can be selectively blocked by curare, the neuronal-type by hexamethonium. The main location of muscle-type receptors is on muscle cells, as described in more detail below. Neuronal-type receptors are located in autonomic ganglia (both sympathetic and parasympathetic), and in the central nervous system.

Muscarinic acetylcholine receptors have a more complex mechanism, and affect target cells over a longer time frame. In mammals, five subtypes of muscarinic receptors have been identified, labeled M1 through M5. All of them function as G protein-coupled receptors, meaning that they exert their effects via a second messenger system. The M1, M3, and M5 subtypes are Gq-coupled; they increase intracellular levels of IP3 and calcium by activating phospholipase C. Their effect on target cells is usually excitatory. The M2 and M4 subtypes are Gi/Go-coupled; they decrease intracellular levels of cAMP by inhibiting adenylate cyclase. Their effect on target cells is usually inhibitory. Muscarinic acetylcholine receptors are found in both the central nervous system and the peripheral nervous system of the heart, lungs, upper gastrointestinal tract, and sweat glands.

Neuromuscular junction

Acetylcholine is the substance the nervous system uses to activate skeletal muscles, a kind of striated muscle. These are the muscles used for all types of voluntary movement, in contrast to smooth muscle tissue, which is involved in a range of involuntary activities such as movement of food through the gastrointestinal tract and constriction of blood vessels. Skeletal muscles are directly controlled by motor neurons located in the spinal cord or, in a few cases, the brainstem. These motor neurons send their axons through motor nerves, from which they emerge to connect to muscle fibers at a special type of synapse called the neuromuscular junction.

When a motor neuron generates an action potential, it travels rapidly along the nerve until it reaches the neuromuscular junction, where it initiates an electrochemical process that causes acetylcholine to be released into the space between the presynaptic terminal and the muscle fiber. The acetylcholine molecules then bind to nicotinic ion-channel receptors on the muscle cell membrane, causing the ion channels to open. Sodium ions then flow into the muscle cell, initiating a sequence of steps that finally produce muscle contraction.

Factors that decrease release of acetylcholine (and thereby affecting P-type calcium channels):

 * 1) Antibiotics (clindamycin, polymyxin)
 * 2) Magnesium: antagonizes P-type calcium channels
 * 3) Hypocalcemia
 * 4) Anticonvulsants
 * 5) Diuretics (furosemide)
 * 6) Eaton-Lambert syndrome: inhibits P-type calcium channels
 * 7) Myasthenia gravis
 * 8) Botulinum toxin: inhibits SNARE proteins

Calcium channel blockers (nifedipine, diltiazem) do not affect P-channels. These drugs affect L-type calcium channels.

Autonomic nervous system
The autonomic nervous system controls a wide range of involuntary and unconscious body functions. Its main branches are the sympathetic nervous system and parasympathetic nervous system. Broadly speaking, the function of the sympathetic nervous system is to mobilize the body for action; the phrase often invoked to describe it is fight-or-flight. The function of the parasympathetic nervous system is to put the body in a state conducive to rest, regeneration, digestion, and reproduction; the phrase often invoked to describe it is "rest and digest" or "feed and breed". Both of these aforementioned systems use acetylcholine, but in different ways.

At a schematic level, the sympathetic and parasympathetic nervous systems are both organized in essentially the same way: preganglionic neurons in the central nervous system send projections to neurons located in autonomic ganglia, which send output projections to virtually every tissue of the body. In both branches the internal connections, the projections from the central nervous system to the autonomic ganglia, use acetylcholine as a neurotransmitter to innervate (or excite) ganglia neurons. In the parasympathetic nervous system the output connections, the projections from ganglion neurons to tissues that do not belong to the nervous system, also release acetylcholine but act on muscarinic receptors. In the sympathetic nervous system the output connections mainly release noradrenaline, although acetylcholine is released at a few points, such as the sudomotor innervation of the sweat glands.

Direct vascular effects
Acetylcholine in the serum exerts a direct effect on vascular tone by binding to muscarinic receptors present on vascular endothelium. These cells respond by increasing production of nitric oxide, which signals the surrounding smooth muscle to relax, leading to vasodilation.

Central nervous system
In the central nervous system, ACh has a variety of effects on plasticity, arousal and reward. ACh has an important role in the enhancement of alertness when we wake up, in sustaining attention and in learning and memory.

Damage to the cholinergic (acetylcholine-producing) system in the brain has been shown to be associated with the memory deficits associated with Alzheimer's disease. ACh has also been shown to promote REM sleep.

In the brainstem acetylcholine originates from the Pedunculopontine nucleus and laterodorsal tegmental nucleus collectively known as the mesopontine tegmentum area or pontomesencephalotegmental complex. In the basal forebrain, it originates from the basal nucleus of Meynert and medial septal nucleus:
 * The pontomesencephalotegmental complex acts mainly on M1 receptors in the brainstem, deep cerebellar nuclei, pontine nuclei, locus coeruleus, raphe nucleus, lateral reticular nucleus and inferior olive. It also projects to the thalamus, tectum, basal ganglia and basal forebrain.
 * Basal nucleus of Meynert acts mainly on M1 receptors in the neocortex.
 * Medial septal nucleus acts mainly on M1 receptors in the hippocampus and parts of the cerebral cortex.

In addition, ACh acts as an important internal transmitter in the striatum, which is part of the basal ganglia. It is released by cholinergic interneurons. In humans, non-human primates and rodents, these interneurons respond to salient environmental stimuli with responses that are temporally aligned with the responses of dopaminergic neurons of the substantia nigra.

Memory
Acetylcholine has been implicated in learning and memory in several ways. The anticholinergic drug scopolamine impairs acquisition of new information in humans and animals. In animals, disruption of the supply of acetylcholine to the neocortex impairs the learning of simple discrimination tasks, comparable to the acquisition of factual information and disruption of the supply of acetylcholine to the hippocampus and adjacent cortical areas produces forgetfulness, comparable to anterograde amnesia in humans.

Myasthenia gravis
The disease myasthenia gravis, characterized by muscle weakness and fatigue, occurs when the body inappropriately produces antibodies against acetylcholine nicotinic receptors, and thus inhibits proper acetylcholine signal transmission. Over time, the motor end plate is destroyed. Drugs that competitively inhibit acetylcholinesterase (e.g., neostigmine, physostigmine, or primarily pyridostigmine) are effective in treating the symptoms of this disorder. They allow endogenously released acetylcholine more time to interact with its respective receptor before being inactivated by acetylcholinesterase in the synaptic cleft (the space between nerve and muscle).

Pharmacology
Blocking, hindering or mimicking the action of acetylcholine has many uses in medicine. Drugs acting on the acetylcholine system are either agonists to the receptors, stimulating the system, or antagonists, inhibiting it. Acetylcholine receptor agonists and antagonists can either have an effect directly on the receptors or exert their effects indirectly, e.g., by affecting the enzyme acetylcholinesterase, which degrades the receptor ligand. Agonists increase the level of receptor activation; antagonists reduce it.

Acetylcholine itself does not have therapeutic value as a drug for intravenous administration because of its multi-faceted action (non-selective) and rapid inactivation by cholinesterase. However, it is used in the form of eye drops to cause constriction of the pupil during cataract surgery, which facilitates quick post-operational recovery.

Nicotinic receptors
Nicotine binds to and activates nicotinic acetylcholine receptors, mimicking the effect of acetylcholine at these receptors. ACh opens a Na+ channel upon binding so that Na+ flows into the cell. This causes a depolarization, and results in an excitatory post-synaptic potential. Thus, ACh is excitatory on skeletal muscle; the electrical response is fast and short-lived. Curares are arrow poisons, which act at nicotinic receptors and have been used to develop clinically useful therapies.

Muscarinic receptors
Muscarinic receptors form G protein-coupled receptor complexes in the cell membranes of neurons and other cells. Atropine is a non-selective competitive antagonist with Acetylcholine at muscarinic receptors.

Cholinesterase inhibitors
Many ACh receptor agonists work indirectly by inhibiting the enzyme acetylcholinesterase. The resulting accumulation of acetylcholine causes continuous stimulation of the muscles, glands, and central nervous system, which can result in fatal convulsions if the dose is high.

They are examples of enzyme inhibitors, and increase the action of acetylcholine by delaying its degradation; some have been used as nerve agents (Sarin and VX nerve gas) or pesticides (organophosphates and the carbamates). Many toxins and venoms produced by plants and animals also contain cholinesterase inhibitors. In clinical use, they are administered in low doses to reverse the action of muscle relaxants, to treat myasthenia gravis, and to treat symptoms of Alzheimer's disease (rivastigmine, which increases cholinergic activity in the brain).

Synthesis inhibitors
Organic mercurial compounds, such as methylmercury, have a high affinity for sulfhydryl groups, which causes dysfunction of the enzyme choline acetyltransferase. This inhibition may lead to acetylcholine deficiency, and can have consequences on motor function.

Release inhibitors
Botulinum toxin (Botox) acts by suppressing the release of acetylcholine, whereas the venom from a black widow spider (alpha-latrotoxin) has the reverse effect. ACh inhibition causes paralysis. When bitten by a black widow spider, one experiences the wastage of ACh supplies and the muscles begin to contract. If and when the supply is depleted, paralysis occurs.

Comparative biology and evolution
Acetylcholine is used by organisms in all domains of life for a variety of purposes. It is believed that choline, a precursor to acetylcholine, was used by single celled organisms billions of years ago for synthesizing cell membrane phospholipids. Following the evolution of choline transporters, the abundance of intracellular choline paved the way for choline to become incorporated into other synthetic pathways, including acetylcholine production. Acetylcholine is used by bacteria, fungi, and a variety of other animals. Many of the uses of acetylcholine rely on its action on ion channels via GPCRs like membrane proteins.

The two major types of acetylcholine receptors, muscarinic and nicotinic receptors, have convergently evolved to be responsive to acetylcholine. This means that rather than having evolved from a common homolog, these receptors evolved from separate receptor families. It is estimated that the nicotinic receptor family dates back longer than 2.5 billion years. Likewise, muscarinic receptors are thought to have diverged from other GPCRs at least 0.5 billion years ago. Both of these receptor groups have evolved numerous subtypes with unique ligand affinities and signaling mechanisms. The diversity of the receptor types enables acetylcholine to create varying responses depending on which receptor types are activated, and allow for acetylcholine to dynamically regulate physiological processes. ACh receptors are related to 5-HT3 (serotonin), GABA, and Glycine receptors, both in sequence and structure, strongly suggesting that they have a common evolutionary origin.

History
In 1867, Adolf von Baeyer resolved the structures of choline and acetylcholine and synthesized them both, referring to the latter as "acetylneurin" in the study. Choline is a precursor for acetylcholine. This is why Frederick Walker Mott and William Dobinson Halliburton noted in 1899 that choline injections decreased the blood pressure of animals. Acetylcholine was first noted to be biologically active in 1906, when Reid Hunt (1870–1948) and René de M. Taveau found that it decreased blood pressure in exceptionally tiny doses.

In 1914, Arthur J. Ewins was the first to extract acetylcholine from nature. He identified it as the blood pressure-decreasing contaminant from some Claviceps purpurea ergot extracts, by the request of Henry Hallett Dale. Later in 1914, Dale outlined the effects of acetylcholine at various types of peripheral synapses and also noted that it lowered the blood pressure of cats via subcutaneous injections even at doses of one nanogram.

The concept of neurotransmitters was unknown until 1921, when Otto Loewi noted that the vagus nerve secreted a substance that inhibited the heart muscle whilst working as a professor in the University of Graz. He named it vagusstoff ("vagus substance"), noted it to be a structural analog of choline and suspected it to be acetylcholine. In 1926, Loewi and E. Navratil deduced that the compound is probably acetylcholine, as vagusstoff and synthetic acetylcholine lost their activity in a similar manner when in contact with tissue lysates that contained acetylcholine-degrading enzymes (now known to be cholinesterases). This conclusion was accepted widely. Later studies confirmed the function of acetylcholine as a neurotransmitter.

In 1936, H. H. Dale and O. Loewi shared the Nobel Prize in Physiology or Medicine for their studies of acetylcholine and nerve impulses.

General bibliography

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license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Acetylcholine


text:
NIH (disambiguation)

NIH is the National Institutes of Health in the United States.

NIH may also refer to:

Organisations

 * National Institute of Health (Armenia)
 * National Institute of Health (Pakistan)
 * National Institute of Homoeopathy, India
 * National Institute of Hydrology, an Indian government body
 * Norwegian School of Sport Sciences (Norges idrettshøgskole), a university in Oslo, Norway

Other uses

 * Not invented here, whereby something from another organization or culture is deemed inferior to something from one's own organization or culture
 * Nih (town), an ancient town in Sistan (modern Iran and Afghanistan)
 * NIH shift, a rearrangement of hydrogen in a molecule
 * Nickel–hydrogen battery (NiH2 or NIH)

title: NIH (disambiguation)


text:
Squash (sport)

Squash, sometimes called squash rackets, is a racket-and-ball sport played by two (singles) or four players (doubles) in a four-walled court with a small, hollow, rubber ball. The players alternate in striking the ball with their rackets onto the playable surfaces of the four walls of the court. The objective of the game is to hit the ball in such a way that the opponent is not able to play a valid return. There are about 20 million people who play squash regularly world-wide in over 185 countries. The governing body of squash, the World Squash Federation (WSF), is recognized by the International Olympic Committee (IOC), and the sport will be included in the Olympic Games, starting with the 2028 Summer Olympics in Los Angeles. The Professional Squash Association (PSA) organizes the pro tour.

History
Squash has its origins in the older game of rackets, which was played in London's prisons in the 19th century. Later, around 1830, boys at Harrow School noticed that a punctured ball, which "squashed" on impact with the wall, offered more variety to the game. The game spread to other schools. The first courts built at Harrow were dangerous because they were near water pipes, buttresses, chimneys, and ledges. Natural rubber was the preferred material for the ball. Students modified their rackets to have a smaller reach and improve their ability to play in these cramped conditions. In 1864, the school built four outside courts.

In the 20th century, the game increased in popularity with various schools, clubs and private individuals building squash courts, but with no set dimensions. The first squash court in North America was at St. Paul's School in Concord, New Hampshire, in 1884. In 1904 in Philadelphia, Pennsylvania, the earliest national association of squash in the world, the United States Squash Racquets Association, now known as U.S. Squash, was formed. In April 1907, the Tennis, Rackets & Fives Association of Queens, New York, which regulated those three sports (fives being a similar sport using hands instead of a racket), established a subcommittee to set standards for squash. In 1912, the association published rules for squash, combining aspects of these three sports.

In 1912, the RMS Titanic had a squash court in first class, available for 8 pence (£12.22 in 2022 terms). The 1st-Class Squash Court was situated on G-Deck. The Spectators Viewing Gallery was one level higher, on F-Deck. Passengers could use the court for one hour unless others were waiting.

In 1923, the Royal Automobile Club hosted a meeting to further discuss the rules and regulations. Five years later, the Squash Rackets Association, now known as England Squash, was formed to set standards for the game in Great Britain and internationally. The rackets were made from one piece English ash, with a suede leather grip and natural gut.

The 1980s witnessed a period of restructuring and consolidation. The Cambridge rackets factory was forced to close in face of the move to graphite rackets, and production was moved to the Far East. Customization of squash rackets has grown over the years as well. There are custom variations on racket head shape, racket balance, and racket weight. The most common racket variation for international singles squash is a teardrop (closed throat) head shape, even balance, and racket weight of 130g. For hardball doubles, the most common variation is an open throat head shape, even balance, and racket weight of 140g.

There are several variations of squash played across the world, although the international version of the sport has become the dominant form. In the United States, a variant of squash known as hardball was traditionally played with a harder ball and differently sized courts. Hardball squash has lost much of its popularity in North America (in favor of the international version). There is doubles squash a variant played by four players. There is also a tennis-like variation of squash known as squash tennis. Finally, racketball, a similar sport played on a squash court (as distinguished from racquetball), has been rebranded as Squash 57 by the World Squash Federation.

Racket
Squash rackets have maximum dimensions of 686 mm (27.0 in) long and 215 mm (8.5 in) wide, with a maximum strung area of 500 square centimeters (77.5 sq in). The permitted maximum weight is 255 g, but most have a weight between 90 and 150 grams (3–5.3 oz.). The strings of the racket usually have a tension of 25–30 pounds.

Ball
Squash balls are between 39.5 and 40.5 mm in diameter and weigh 23 to 25 grams. They are made with two pieces of rubber compound, glued together to form a hollow sphere and buffed to a matte finish. Different balls are provided for varying temperature and atmospheric conditions and standards of play: more experienced players use slow balls that have less bounce than those used by less experienced players (slower balls tend to "die" in court corners, rather than "standing up" to allow easier shots). Squash balls must be hit dozens of times to warm them up at the beginning of a session; cold squash balls have very little bounce. Small colored dots on the ball indicate its dynamic level (bounciness). The "double-yellow dot" ball, introduced in 2000, is the competition standard, replacing the earlier "yellow-dot" ball. There is also an "orange dot" ball for use at high altitudes. The recognized colors are:

Some ball manufacturers such as Dunlop use a different method of grading balls based on experience. They still have the equivalent dot rating but are named to help choose a ball that is appropriate for one's skill level. The four different ball types are Intro (Blue dot, 140% of Pro bounce), Progress (Red dot, 120% of Pro bounce), Competition (single yellow dot, 110% of Pro bounce) and Pro (double yellow dot).

Many squash venues mandate the use of shoes with non-marking tread and eye protection. Some associations require that all juniors and doubles players must wear eye protection. The National Institutes of Health recommends wearing goggles with polycarbonate lenses.

Court

The squash court is a playing surface surrounded by four walls. The court surface contains a front line separating the front and back of the court and a half court line, separating the left and right sides of the back portion of the court, creating three 'boxes': the front half, the back left quarter and the back right quarter. The back two boxes contain smaller service boxes.

The court's four walls are divided into a front wall, two side walls, and a back wall. An 'out line' runs along the top of the front wall, descending along the side walls to the back wall. The bottom line of the front wall marks the top of the 'tin', a half meter-high metal area. The middle line of the front wall is the service line. The dimensions of the court are:

North American hardball doubles courts are larger than international singles courts because of a hard ball that has a much faster pace. With double the number of players, the doubles court needs to be significantly bigger than a singles court. The doubles court should measure 25 feet wide by 45 feet long and have a ceiling height of at least 24 feet but preferably 26.

Service
The players spin a racket to decide who serves first. This player starts the first rally by electing to serve from either the left or right service box. For a legal serve, one of the server's feet must be in the service box, not touching any part of the service box lines, as the player strikes the ball. After being struck by the racket, the ball must strike the front wall above the service line and below the out line and land in the opposite back quarter court. The receiving player can choose to volley a serve after it has hit the front wall. If the server wins the point, the two players switch sides for the following point. If the server loses the point, the opponent then serves, and can serve from either box.

Play
After the serve, the players take turns hitting the ball against the front wall, above the tin and below the out line. The ball may strike the side or back walls at any time, as long as it hits below the out line. It must not hit the floor after hitting the racket and before hitting the front wall. A ball landing on either the out line or the line along the top of the tin is considered to be out. After the ball hits the front wall, it is allowed to bounce once on the floor (and any number of times against the side or back walls) before a player must return it. Players may move anywhere around the court, but accidental or deliberate obstruction of the other player's movements is forbidden and could result in a let or a stroke. Players typically return to the centre of the court after making a shot, as it is the optimal position in the court to receive the opponent's shot. The centre of the court is typically referred to as "the T", named after the shape of the floor lines.

Strategy and tactics
A key strategy in squash is known as "dominating the T" (the intersection of the red lines near the centre of the court, shaped like the letter "T", where the player is in the best position to retrieve the opponent's next shot). Skilled players will return a shot, and then move back toward the "T" before playing the next shot. From this position, the player can quickly access any part of the court to retrieve the opponent's next shot with a minimum of movement and possibly maximising the movement required by the opponent to answer the returned shot.

A common tactic is to hit the ball straight up the side walls to the back corners; this is the basic squash shot, referred to as a "rail", straight drive, wall, or "length". After hitting this shot, the player will then move to the centre of the court near the "T" to be well placed to retrieve the opponent's return. Attacking with soft or "short" shots to the front corners (referred to as "drop shots") causes the opponent to cover more of the court and may result in an outright winner. Boasts or angle shots are deliberately struck off one of the side walls before the ball reaches the front. They are used for deception and again to cause the opponent to cover more of the court. Rear wall shots float to the front either straight or diagonally drawing the opponent to the front. Advantageous tactical shots are available in response to a weak return by the opponent if stretched, the majority of the court being free to the striker. Nicks are when the ball comes into contact with the intersection of the floor and any sidewall.

Rallies between experienced players may involve 30 or more shots and therefore a very high premium is placed on fitness, both aerobic and anaerobic. As players become more skilled and, in particular, better able to retrieve shots, points often become a war of attrition. At higher levels of the game, the fitter player has a major advantage.

The ability to change the direction of the ball at the last instant is also a tactic used to unbalance the opponent. Expert players can anticipate the opponent's shot a few tenths of a second before the average player, giving them a chance to react sooner.

Depending on the style of play, it is common to refer to squash players as

 * Power players: powerful shots to take time away from their opponent. For example, John White, Omar Mosaad, Mohamed El Shorbagy, Nouran Gohar
 * Shotmakers: accurate shots to take time away from their opponent. For example, Jonathon Power, Ramy Ashour, Amr Shabana, James Willstrop.
 * Retrievers: excellent retrieval to counter power and accuracy and to return shots more quickly to take time away from their opponent. For example, Peter Nicol, Grégory Gaultier, Nicol David.
 * Attritional players: a consistently high-paced game both from shot speed and running speed to wear their opponent down over time. For example, David Palmer, Nick Matthew, Jansher Khan, Jahangir Khan.

Interference and obstruction
Interference and obstruction are an inevitable aspect of squash, since two players are confined within a shared space. Generally, the rules entitle players to a direct straight-line access to the ball, room for a reasonable swing and an unobstructed shot to any part of the front wall. When interference occurs, a player may appeal for a "let" and the referee (or the players themselves if there is no official) then interprets the extent of the interference. The referee may allow a let and the players then replay the point or award a "stroke" to the appealing player (meaning that he is declared the winner of that point) depending on the degree of interference, whether the interfering player made an adequate effort to avoid interfering, and whether the player interfered with was likely to have hit a winning shot had the interference not occurred. An exception occurs when the interfering player is directly in the path of the other player's swing, effectively preventing the swing, in which case a stroke is always awarded.

When it is deemed that there has been little or no interference, the rules provide that no let is to be allowed in the interests of continuity of play and the discouraging of spurious appeals for lets. Because of the subjectivity in interpreting the nature and magnitude of interference, awarding (or withholding) of lets and strokes is often controversial.

Interference also occurs when a player's shot hits their opponent prior to hitting the front wall. If the ball was travelling towards the side wall when it hit the opponent, or if it had already hit the side wall and was travelling directly to the front wall, it is usually a let. However, it is a stroke to the player who hit the ball if the ball was travelling straight to the front wall when the ball hit the opponent, without having first hit the side wall. Generally, after a player has been hit by the ball, both players stand still; if the struck player is standing directly in front of the player who hit the ball, he loses the stroke; if he is not straight in front, a let is played. If it is deemed that the player who is striking the ball is deliberately trying to hit his opponent, they will lose the stroke. An exception occurs when the player hitting the ball has "turned", i.e., letting the ball pass them on one side, but then hitting it on the other side as it came off the back wall. In these cases, the stroke goes to the player who was hit by the ball.

Referee
The referee is usually a certified position issued by the club or assigned squash league. Any conflict or interference is dealt with by the referee. The referee may also take away points or games due to improper etiquette regarding conduct or rules. The referee is also usually responsible for the scoring of games. Three referees are usually used in professional tournaments. The Central referee has responsibility to call the score and make decisions with the two side referees.

Point-a-Rally to 11
Games are played according to point-a-rally scoring (PARS) to 11 points. PARS is almost universally preferred by the game's top professionals and is the current official scoring system for all levels of professional squash tournaments. In PARS, the winner of a rally receives a point, regardless of whether they were the server or returner. Games are played to 11 and must be won by two points. That is, if the score reaches 10–10, play continues until one player wins by two points. Competition matches are usually played to "best-of-five" games (i.e., the first player to win three games).

Squash can also be played with different scoring systems, such as PARS to 15, traditional English or Hand-in-Hand-Out (HiHo) scoring to 9, or RAM scoring (see below). Players often experience PARS and Hi-Ho as requiring different tactics and player attributes.

Point-a-Rally to 15
Point-a-rally scoring to 15 was used for the World Championships between 1989 and 2003. PARS to 15, with the tiebreak being two clear points (as per standard PARS) from 14–14, was used in many amateur leagues because PARS to 11 was considered too short. This system fell out of favor in 2004 when the Professional Squash Association (PSA) decided to switch to PARS to 11. Games were considered to last too long and the winner would usually be the fitter player, not necessarily the better player.

English/Hand-In-Hand-Out to 9
Known as English or hand-in-hand-out scoring, under this system, if the server wins a rally, they receive a point, while if the returner wins rally, only the service changes (i.e., the ball goes "hand-out") and no point is given. The first player to reach nine points wins the game. However, if the score reaches 8–8, the player who was first to reach eight decides whether the game will be played to nine, as before (called "set one"), or to 10 (called "set two"). This scoring system was formerly preferred in Britain, and also among countries with traditional British ties, such as Australia, Canada, Pakistan, South Africa, India and Sri Lanka.

RAM
The RAM scoring system is a proposed new scoring system created by former World Champion, Ramy Ashour and co-founded by Osama Khalifa. This consists of playing a best of five games. Each game is three minutes long; however, this only refers to the three minutes in play. The 'downtime' in between the end of a rally and a serve is not counted. Once the time is up, the clock stops, and the leading player needs to win a final point. If the player who is behind wins the point the game continues until the trailing player catches up and wins one more point than the initially leading player.

For example, Player one is leading 5–3 and the clock stops. Player two wins the next two points and the score is 5–5. Whoever wins the next point wins the game. This is called sudden death. If the score is 0–0 when the clock stops the clock is reset and the game restarts. For Let Calls the clock reverts to the start time of that point. Further rules include that there must be a referee and a time keeper to make this match official. Players have two minutes of rest between games, and all other standard PSA and WSF rules apply.

Transition from English/HiHo to PARS 11
In 2004, the Professional Squash Association (PSA) decided to switch to PARS 11. This decision was ratified in 2009 when the World Squash Federation confirmed the switch to the PARS 11 scoring system. Since that time, almost all professional and league games have been played according to PARS to 11. One of the reasons for switching to PARS was that long, taxing matches became less frequent and promoters could more easily predict match and session length. Gawain Briars, who served as the Executive Director of the Professional Squash Association when the body decided to switch to PARS in 2004 hoped that PARS would make the "professional game more exciting to watch, [and] then more people will become involved in the game and our chances of Olympic entry may be enhanced."

One of the problems with English or Hi-Ho scoring is that games often last longer as players continually win service before losing service to the other player without the score being affected. Consequently, the winner is more often than not the fitter athlete. Moreover, English or Hi-Ho scoring can encourage players to play defensively with the aim of wearing down one's opponent before winning by virtue of one's fitness. Such exhausting, defensive play can affect player's prospects in knock-out tournaments and does not make for riveting TV. In English or Hi-Ho, one player might win by 9–0 despite the opponent having repeatedly won service, but without converting that service into actual points.

For the World Championships: HiHo to 9 was used until 1988; PARS to 15 from 1989 to 2003; and PARS to 11 from 2004. For the British Open: HiHo to 9 was used until 1994; PARS to 15 from 1995 to 2003; and PARS to 11 from 2004.

The WSF's decision to switch to PARS 11 proved controversial in the United Kingdom and Commonwealth where games were usually played according to English or Hi-Ho. When the Veterans Squash Rackets Club of Great Britain surveyed their members in 2012, they found that 80% of their members were against switching from HiHo to PARS. President Philip Ayton argued that PARS would "kill the essence of the game." Ayton was particularly concerned that the "great comebacks" that characterised English or Hi-Ho when "the player who is down in a game can still attack when in hand serving" would disappear as PARS fostered an "ultra-defensive attitude, because every rally counts the same."

Jahangir Khan has countered that PARS actually made the game far more attacking, but diminished the psychological aspect of the game: "With the nine points scoring system, matches were more mental and physical and could go longer, but now with the 11-point system, every rally counts, and even if you go behind you can still recover. That makes it a lot more attacking." Maj Madan, one of the game's top referees, similarly stated that PARS had "destroyed the fitness element and, more importantly, the cerebral magic of the…game." His comments were unearthed when an email chain of referees discussing the problem of shorter and shorter squash matches was leaked in 2011.

Contribution to health
Squash provides an excellent cardiovascular workout. Players can expend approximately 600–1,000 food calories (3,000–4,000 kJ) every hour playing squash, according to English or Hi-Ho scoring. The sport also provides a good upper- and lower-body workout by exercising both the legs in running around the court and the arms and torso in swinging the racket. In 2003, Forbes rated squash as the number-one healthiest sport to play. However, one study has implicated squash as a cause of possible fatal cardiac arrhythmia and argued that squash is an inappropriate form of exercise for older men with heart disease.

Around the world
As of November 2019, there were players from eighteen countries in the top fifty of the men's world rankings, with Egypt dominating with fifteen players, six of whom were in the top ten, including ranks one through four. Similarly, the women's world rankings featured players from sixteen countries, again led by Egypt taking thirteen spots of the top fifty, whilst holding spots one through four in the world.

The men's and women's Professional Squash Association tour, men's rankings and women's rankings are run by the Professional Squash Association (PSA).

The Professional Squash Tour is a tour based in the United States.

Inclusion in multi-sport events
Squash has been featured regularly at the multi-sport events of the Commonwealth Games and Asian Games since 1998. Squash is also a regular sport at the Pan American Games since 1995. Squash players and associations have lobbied for many years for the sport to be accepted into the Olympic Games. Squash narrowly missed being instated for the 2012 London Games and the 2016 Rio de Janeiro Games (missed out again as the IOC assembly decided to add golf and rugby sevens to the Olympic programme). Squash also was not selected as an event in the 2020 Olympic Games. At the 125th IOC Session in Buenos Aires, the IOC voted for Wrestling instead of Squash or Baseball/Softball. The usual reason cited for the failure of the sport to be adopted for Olympic competition is that it is difficult for spectators to follow the action, especially via television. Previous world number one Peter Nicol stated that he believed squash had a "very realistic chance" of being added to the list of Olympic sports for the 2016 Olympic Games, but it ultimately lost out to golf and rugby sevens. Squash has been part of the World Games since 1997.

Squash was accepted as a demonstration sport for the 2018 Summer Youth Olympics. The World Squash Federation had hoped that this inclusion would create a strong bid for a potential inclusion at the 2024 Summer Olympics.

Although not included in the 2024 Summer Olympics, squash received approval from the International Olympic Committee for inclusion in the 2028 Summer Olympics in Los Angeles, on 16 October 2023.

Major tournaments

 * World Open Championship
 * World Tour Finals
 * World Team Championships
 * British Open
 * Tournament of Champions
 * US Open
 * Hong Kong Open
 * Qatar Classic
 * Windy City Open
 * El Gouna International
 * Summer Olympics
 * World Games
 * Commonwealth Games
 * Asian Games

Players, records and rankings

The (British) Squash Rackets Association (now known as England Squash) conducted its first British Open championship for men in December 1930, using a "challenge" system. Charles Read was designated champion in 1930, but he was beaten in home and away matches by Don Butcher, who was then recorded as the champion for 1931. The championship continues to this day, but it has been conducted with a "knockout" format since 1947.

The women's championship started in 1921, and it has been dominated by relatively few players: Joyce Cave, Nancy Cave, Cecily Fenwick (England) in the 1920s; Margot Lumb and Susan Noel (England) in the 1930s; Janet Morgan (England) in the 1950s; Heather McKay (Australia) in the 1960s and 1970s; Vicki Cardwell (Australia) and Susan Devoy (New Zealand) in the 1980s; Michelle Martin and Sarah Fitz-Gerald (Australia) in the 1990s; and Nicol David (Malaysia) in the 2000s.

The Men's British Open has similarly been dominated by relatively few players: F. D. Amr Bey (Egypt) in the 1930s; Mahmoud Karim (Egypt) in the 1940s; brothers Hashim Khan and Azam Khan (Pakistan) in the 1950s and 1960s; Jonah Barrington (Great Britain and Ireland) and Geoff Hunt (Australia) in the 1960s and 1970s; Jahangir Khan (Pakistan) 1980s; Jansher Khan (Pakistan) in the 1990s; and more recently, David Palmer and Nick Matthew.

The World Open professional championship was inaugurated in 1976 and serves as the main competition today. Jansher Khan holds the record of winning eight World titles followed by Jahangir Khan with six, Geoff Hunt & Amr Shabana four, Nick Matthew & Ramy Ashour three. The women's record is held by Nicol David with eight wins followed by Sarah Fitzgerald five, Susan Devoy four, and Michelle Martin three.

Heather McKay remained undefeated in competitive matches for 19 years (between 1962 and 1981) and won sixteen consecutive British Open titles between 1962 and 1977.

Current rankings
The Professional Squash Association (PSA) publishes monthly rankings of professional players:

title: Squash (sport)


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Albert Brudzewski

Albert Brudzewski, also Albert Blar (of Brudzewo), Albert of Brudzewo or Wojciech Brudzewski (in Latin, Albertus de Brudzewo; c.1445–c.1497) was a Polish astronomer, mathematician,  philosopher and diplomat.

Life
Albert (in Polish, Wojciech), who would sign himself "de Brudzewo" ("of Brudzewo"), was born about 1445, in Brudzewo, near Kalisz. Scant information exists about his early life. It is only known that as a 23-year-old he matriculated at the Kraków Academy (now Jagiellonian University), where he remained through nearly all his life, teaching there for two decades. He served as the academy's dean, as procurator (administrator of its property), and as head of the Bursa Hungarorum ("Hungarians' Dormitory").

Albert is remembered as a remarkable teacher. At the Kraków Academy he impressed students by his extraordinary knowledge of literature, and taught mathematics and astronomy. When in 1490 he became a bachelor of theology, he also lectured on Aristotle's philosophy. These lectures were attended by Nicolaus Copernicus, who enrolled at the academy in 1491. A major accomplishment of Albert's was his modernization of the teaching of astronomy by introducing the most up-to-date texts.

Albert was well versed in Georg von Peuerbach's Theory of the Planets and Regiomontanus' Astronomical Tables. He was skeptical of the geocentric system. He was the first to state that the Moon moves in an ellipse and always shows its same side to the Earth.

He drew up tables for calculating the positions of heavenly bodies. In 1482 he wrote a Commentariolum super Theoricas novas planetarum Georgii Purbachii [...] per Albertum de Brudzewo — a commentary on Georg von Peuerbach's text, Theoricae novae planetarum – New Theories of the Planets — published in Milan, Mediolani, in 1495, by his pupil, Jan Otto de Kraceusae with this title Commentaria utilissima in theoricis planetarum.

Besides Copernicus, Albert's students included the mathematician Bernard Wapowski and the German poet and Renaissance humanist, Conrad Celtis, who in Kraków established the first Central European literary society, Sodalitas Litterana Vistulana.

In 1495, at the behest of Cardinal Fryderyk Jagiellończyk (Frederick Jagiellon), Brudzewski moved to Vilnius as secretary to Grand Duke of Lithuania Aleksander Jagiellon, who would later become King Alexander of Poland. He served the Grand Duke as a diplomat; one of his most important missions involved negotiations with Muscovy's Tsar Ivan the Terrible. It was in Vilnius that Albert wrote his treatise, Conciliator, the original of which has not yet been found.

Albert of Brudzewo died in Vilnius. The exact date of his death is not known; some sources state that he died at the age of fifty.

Albert Brudzewski and Averroes
Albert of Brudzewo or Albert Brudzewski was seen as influential and persuasive astronomer, a fictionalist, and an opponent of Averroes. Averroes disagreed with the majority of the astronomer Ptolemy's work. He believed that Ptolemy's devices and principles disobeyed the fundamental principles and basic consequences of Aristotle's physics. Averroes worked to replace the Ptolemaic astronomical system with a novel system that was similar to a system created by Eudoxus. Albert Brudzewski disagreed and criticized Averroes immediately. The major dispute was the figuring out the number of celestial orbs or spheres that lay in the heavens. Averroes refused to believe that there was a ninth sphere in the heavens. He believed that the creation of all celestial beings had to arise from the stars, but the ninth sphere did not possess any stars, so this could not be true. Albert Brudzewski argued with this and said that the heavens possessed more than ten spheres. He believed that the Sun itself had three spheres and the planets had their own as well.

To make sense and clarify to his followers, Brudzewski said that the terms 'orb' or 'sphere' had three meanings of interpretation. The first meaning could be the whole entire heavens was designated into a single object which was the orb or sphere. This object was not separate from the whole heavens yet it could exist by itself. The second meaning he paralleled it to the sphere or orb from George Peurbach's Theoricae novae planetarum although it was unconventional, it still existed in the heavens. The third meaning or clarification of orb was an orb that was aligned with the Earth. The third meaning was actually a collection of orbs that was crucial to the motion of a planet.

Albert Brudzewski further disputes Averroes by depending on the assumptions of Aristotle. He said that Aristotle demonstrated and verified five claims about the heavens that could disprove Averroes. The first claim was that the heavens was a simple being. The second claim was that because the heavens was a simple being, the motion of the being also had to be simple and uncomplicated. There could only be one motion and it had to follow the laws of nature. The third claim was that any motion that did not follow the laws of nature had to have an addition motion that did follow the laws of nature. The fourth claim was that a single sphere or orb could not be moved by several motions because it was a simple body. The fifth claim was that any superior or greater orb could have an impact on lesser orbs and spheres but the lesser orbs and spheres could not have any leverage on the superior's ones.

To finally disprove Averroes, Albert Brudzewski mentions the three recognizable motions of the sphere of fixed stars. The first motion was that the sphere possessed a daily rotation that occurred from the East to the West. The second motion was movement of the sphere in the opposition direction from West to East. The third motion was a cyclical motion that Brudzewski named trepidation. Brudzewski gave these three motions to the last three spheres respectively. With the assumptions of Aristotle as well as the motions of the sphere of the fixed stars, Brudzewski is able to prove that Averroes is wrong about the number of celestial spheres in the heavens.

Albert Brudzewski's Views on the Heavens and Planetary Motion
Albert Brudzewski was known as a fictionalist. He did not think that the motions of the heavens were understood by any human. Richard of Wallingford, an astronomer in the 1300s, had an opposing view for the spheres of the planets. He claimed that no mortal knows whether eccentrics truly exist in the spheres of the planets, but spirits could give humans revelations about the true planetary motion of the heavens through mathematicians. This claim limits the astronomical knowledge of mortals and suggests that spirits do not have the same limitations. Brudzewski acknowledges the existence of these viewpoints but criticized their validity. To astronomers, spirits had an accurate knowledge of the number of celestial orbs. Although, he did not want to discredit the ability of mortals to make claims based on astronomical observations. Albert Brudzewski made the claim for the fundamental principle of astrology that the heavens exert causal influences on the earth.

The paths of planets were thought to be moved by orbs instead of circles. This was a claim by Brudzeski about causal relationships between the planets and their motion. With this view, he disagreed with Averroes about the number of orbs, the concept of epicycles and eccentric circles, and on theoretical orbs. Brudzewski was seen as a source for some of Copernicus's work on orbs, specifically with the Tusi Couple.

Brudzewski's views on Tusi's Couple
Tusi's couple was known as an epicycle arrangement that creates straight line motion of the planets, created by Copernicus. Some think that Brudzewski is the source for Copernicus's model of the Tusi couple. Albert does account for the moon and its double epicycles where he mentions a spot on the moon. The spot on the moon is the problem of explaining the appearance of the face of the moon when always viewing the Earth. These views were not aligned with the Tusi couple. Although, it is speculated that Copernicus could have encountered such a model, where the primary epicycle carries the center of a second epicycle. This is not the Tusi couple, but it could be slightly changed to match its model. The spot on the moon that is always viewed from the Earth would not appear if there was no epicyclical motion of the moon. The motion of the moon was termed as "prosneusis motion" which was part of the lunar theory. This motion means motion of inclination and turning, which corresponds to the single epicycle in Ptolemy's theory of the moon, and the two epicycles in Brudzewski's model.

Brudzewski was aware of the possibility of linear motions from circular motions based on his model of Mercury's motion. This could be an alternative way that Copernicus generated his idea of linear motion for the Tusi couple. Although it seems that Copernicus used Albert's ideas, he highly relied on Islamic sources for the Tusi couple. Copernicus's parameters for the moon are exactly the same as those of Ibn ash-Shātir. It is unclear where Copernicus truly got his ideas.

title: Albert Brudzewski


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User talk:Mobo85

Hello there, welcome to the 'pedia! I hope you like the place and decide to stay. If you need any questions answered about the project then check out Help or drop me a line. Cheers! BTW, thanks for starting the Born in the U.S.A. article. --maveric149

You're welcome, but I didn't start the article. I just corrected the spelling. Thank you, though. 4/8/2006

User categorization
You were listed on the Wikipedians/New Jersey page as living in or being associated with New Jersey. As part of the User categorisation project, these lists are being replaced with user categories. If you would like to add yourself to the category that is replacing the page, please visit Category:Wikipedians in New Jersey for instructions. Al 15:35, August 29, 2005 (UTC)

Proposed deletion of Aliki Theofilopoulous Grafft

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Nomination of Aliki Theofilopoulos Grafft for deletion
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title: User talk:Mobo85


text:
65 BC

The year 65 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Consulship of Cotta and Torquatus (or, less frequently, the year 689 Ab urbe condita). The denomination 65 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

Roman Republic

 * In response to the illegal exercise of citizen rights by foreigners, the Roman Senate passes the Lex Papia, which expels all foreigners from Rome
 * Tigranes of Armenia is defeated and captured by Pompey, thus ending all hostilities on the northeastern frontier of Rome.
 * Pompey the Great subjugates the kingdom of Iberia and makes Colchis a Roman province.

Western Han Empire

 * 9th year of the reign of Emperor Xuan of Han

Births

 * December 8 – Horace, Roman poet (d. 8 BC)
 * Gaius Asinius Pollio, Roman orator, poet and historian (d. AD 4)

Deaths

 * Xiphares, son of Mithridates VI (b. c. 85 BC)

title: 65 BC


text:
64 BC

Year 64 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Caesar and Figulus (or, less frequently, year 690 Ab urbe condita). The denomination 64 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

Roman Republic

 * Pompey destroys the kingdom of Pontus; king Mithridates VI commits suicide after escaping to the Crimea.
 * Pompey annexes Syria and captures Jerusalem, annexing Judea.

Syria

 * King Antiochus XIII Asiaticus is deposed and killed by the Syrian chieftain Sampsiceramus I – this is considered by some the end of the Seleucid dynasty.
 * 64 BC Syria earthquake, mentioned in catalogues of historical earthquakes. It affected the region of Syria and may have caused structural damage in the city of Jerusalem.

Births

 * Marcus Valerius Messalla Corvinus, Roman general and consul (d. AD 8)
 * Nicolaus of Damascus, Jewish historian and philosopher (approximate date)
 * Strabo, Greek philosopher and historian in Amaseia

Deaths

 * Antiochus XIII Asiaticus, king of the Seleucid Empire

title: 64 BC