Camera

A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura (Latin for "dark chamber"), an early mechanism for projecting images. The modern camera evolved from the camera obscura.

Cameras may work with the light of the visible spectrum or with other portions of theelectromagnetic spectrum. A camera generally consists of an enclosed hollow with an opening (aperture) at one end for light to enter, and a recording or viewing surface for capturing the light at the other end. A majority of cameras have a lens positioned in front of the camera's opening to gather the incoming light and focus all or part of the image on the recording surface. The diameter of the aperture is often controlled by a diaphragm mechanism, but some cameras have a fixed-size aperture. Most 20th century cameras used photographic film as a recording surface, while the majority of new ones now use an electronic image sensor.

The still camera takes one photo each time the user presses the shutter button. A typical movie camera continuously takes 24 film frames per second as long as the user holds down the shutter button, or until the shutter button is pressed a second time.

From its inception, the camera has been instrumental in the recording of still images from then-present surroundings, and further modifications led to the development of motion picture sequences in the late 19th century. Cameras and the exhibition of camera-captured images are widely used in both professional and consumer settings in the 21st century for both mass and interpersonal communication purposes.

History

Main article: History of the camera

The forerunner to the photographic camera was the camera obscura, a Latin name literally meaning a dark room but more generally "...a darkened chamber or box, into which light is admitted through a pinhole (later a convex lens), forming an image of external objects on a surface of paper or glass, etc., placed at the focus of the lens". In the 6th century, Greek mathematician and architect Anthemius of Tralles used a type of camera obscura in his experiments. The camera obscura was described by the Arabic scientist Ibn al-Haytham (Alhazen) in his Book of Optics(1015–1021). Scientist-monk Roger Bacon also studied the matter. The actual name of camera obscura was applied by mathematician and astronomer Johannes Kepler in his Ad Vitellionem paralipomena of 1604. He later added a lens and made the apparatus transportable, in the form of a tent. Irish scientist Robert Boyle and his assistant Robert Hooke developed a portable camera obscura in the 1660s.

The first camera obscura that was small enough for practical use as a portable drawing aid was built by Johann Zahn in 1685. At that time there was no way to preserve the images produced by such cameras except by manually tracing them. However, it had long been known that various substances were bleached or darkened or otherwise changed by exposure to light. Seeing the magical miniature pictures that light temporarily "painted" on the screen of a small camera obscura inspired several experimenters to search for some way of automatically making highly detailed permanent copies of them by means of some such substance.

Early photographic cameras were usually in the form of a pair of nested boxes, the end of one carrying the lens and the end of the other carrying a removable ground glass focusing screen. By sliding them closer together or farther apart, objects at various distances could be brought to the sharpest focus as desired. After a satisfactory image had been focused on the screen, the lens was covered and the screen was replaced with the light-sensitive material. The lens was then uncovered and the exposure continued for the required time, which for early experimental materials could be several hours or even days. The first permanent photograph of a camera image was made in 1826 by Joseph Nicéphore Niépce using a sliding wooden box camera made by Charles and Vincent Chevalier in Paris.

Similar cameras were used for exposing the silver-surfaced copper Daguerreotype plates, commercially introduced in 1839, which were the first practical photographic medium. The collodion wet plate process that gradually replaced the Daguerreotype during the 1850s required photographers to coat and sensitize thin glass or iron plates shortly before use and expose them in the camera while still wet. Early wet plate cameras were very simple and little different from Daguerreotype cameras, but more sophisticated designs eventually appeared. The Dubroni of 1864 allowed the sensitizing and developing of the plates to be carried out inside the camera itself rather than in a separate darkroom. Other cameras were fitted with multiple lenses for photographing several small portraits on a single larger plate, useful when making cartes de visite. It was during the wet plate era that the use of bellows for focusing became widespread, making the bulkier and less easily adjusted nested box design obsolete.

For many years, exposure times were long enough that the photographer simply removed the lens cap, counted off the number of seconds (or minutes) estimated to be required by the lighting conditions, then replaced the cap. As more sensitive photographic materials became available, cameras began to incorporate mechanical shutter mechanisms that allowed very short and accurately timed exposures to be made.

The electronic video camera tube was invented in the 1920s, starting a line of development that eventually resulted in digital cameras, which largely supplanted film cameras after the turn of the 21st century.

Mechanics

Image capture

Traditional cameras capture light onto photographic film or photographic plate. Video and digital cameras use an electronic image sensor, usually a charge coupled device (CCD) or a CMOS sensor to capture images which can be transferred or stored in a memory card or other storage inside the camera for later playback or processing.

Cameras that capture many images in sequence are known as movie cameras or as ciné cameras in Europe; those designed for single images are still cameras. However these categories overlap as still cameras are often used to capture moving images in special effects work and many modern cameras can quickly switch between still and motion recording modes. A video camera is a category of movie camera that captures images electronically (either using analogue or digital technology).

Lens

Main articles: Photographic lens and Photographic lens design

The lens of a camera captures the light from the subject and brings it to a focus on the film or detector. The design and manufacture of the lens is critical to the quality of the photograph being taken. The technological revolution in camera design in the 19th century revolutionized optical glass manufacture and lens design with great benefits for modern lens manufacture in a wide range of optical instruments from reading glasses to microscopes. Pioneers included Zeiss and Leitz.

Camera lenses are made in a wide range of focal lengths. They range from extreme wide angle, wide angle, standard, medium telephoto and telephoto. Each lens is best suited a certain type of photography. The extreme wide angle may be preferred for architecture because it has the capacity to capture a wide view of a building. The normal lens, because it often has a wide aperture, is often used for street and documentary photography. The telephoto lens is useful for sports, and wildlife but it is more susceptible to camera shake.

Focus

Due to the optical properties of photographic lenses, only objects within a limited range of distances from the camera will be reproduced clearly. The process of adjusting this range is known as changing the camera's focus. There are various ways of focusing a camera accurately. The simplest cameras have fixed focus and use a small aperture and wide-angle lens to ensure that everything within a certain range of distance from the lens, usually around 3 metres (10 ft) to infinity, is in reasonable focus. Fixed focus cameras are usually inexpensive types, such as single-use cameras. The camera can also have a limited focusing range or scale-focus that is indicated on the camera body. The user will guess or calculate the distance to the subject and adjust the focus accordingly. On some cameras this is indicated by symbols (head-and-shoulders; two people standing upright; one tree; mountains).

Rangefinder cameras allow the distance to objects to be measured by means of a coupled parallax unit on top of the camera, allowing the focus to be set with accuracy. Single-lens reflex camera sallow the photographer to determine the focus and composition visually using the objective lens and a moving mirror to project the image onto a ground glass or plastic micro-prism screen. Twin-lens reflex cameras use an objective lens and a focusing lens unit (usually identical to the objective lens.) in a parallel body for composition and focusing. View cameras use a ground glass screen which is removed and replaced by either a photographic plate or a reusable holder containing sheet film before exposure. Modern cameras often offer autofocus systems to focus the camera automatically by a variety of methods.

Auto-focus systems can capture a subject a variety of ways; here, the focus is on the person's image in the mirror.

19th century studio camera, with bellows for focusing

Camera obscura

October 2011: Some cameras have post focusing and now available for pre-order, but the price were relatively high. Post focusing means take the pictures first and then focusing later at the Personal Computer. The camera uses many tiny lenses with different focal length to capture light from every angle of a scene and is called plenoptics technology. The current Plenoptic camera can serve as has 40,000 lenses working together to grab the optimal picture.

Exposure control

The size of the aperture and the brightness of the scene controls the amount of light that enters the camera during a period of time, and the shutter controls the length of time that the light hits the recording surface. Equivalent exposures can be made with a larger aperture and a faster shutter speed or a corresponding smaller aperture and with the shutter speed slowed down.

Shutters

Main article: Shutter (photography)

Although a range of different shutter devices have been used during the development of the camera only two types have been widely used and remain in use today.

The Leaf shutter or more precisely the in-lens shutter is a shutter contained within the lens structure, often close to the diaphragm consisting of a number of metal leaves which are maintained under spring tension and which are opened and then closed when the shutter is released. The exposure time is determined by the interval between opening and closing. In this shutter design, the whole film frame is exposed at one time. This makes flash synchronisation much simpler as the flash only needs to fire once the shutter is fully open. Disadvantages of such shutters are their inability to reliably produce very fast shutter speeds ( faster than 1/500th second or so) and the additional cost and weight of having to include a shutter mechanism for every lens.

The focal-plane shutter operates as close to the film plane as possible and consists of cloth curtains that are pulled across the film plane with a carefully determined gap between the two curtains (typically running horizontally) or consisting of a series of metal plates (typically moving vertically) just in front of the film plan. The focal-plane shutter is primarily associated with the single lens reflex type of cameras, since covering the film rather than blocking light passing through the lens allows the photographer to view through the lens at all times except during the exposure itself. Covering the film also facilitates removing the lens from a loaded camera (many SLRs have interchangeable lenses).

Complexities

Professional medium format SLR cameras (typically using 120/220 roll film) use a hybrid solution, since such a large focal-plane shutter would be difficult to make and/or may run slowly. A manually inserted blade known as a dark slide allows the film to be covered when changing lenses or film backs. A blind inside the camera covers the film prior to and after the exposure (but is not designed to be able to give accurately controlled exposure times) and a leaf shutter that is normally open is installed in the lens. To take a picture, the leaf shutter closes, the blind opens, the leaf shutter opens then closes again, and finally the blind closes and the leaf shutter re-opens (the last step may only occur when the shutter is re-cocked).

Using a focal-plane shutter, exposing the whole film plane can take much longer than the exposure time. The exposure time does not depend on the time taken to make the exposure over all, only on the difference between the time a specific point on the film is uncovered and then covered up again. For example an exposure of 1/1000 second may be achieved by the shutter curtains moving across the film plane in 1/50th of a second but with the two curtains only separated by 1/20th of the frame width. In fact in practice the curtains do not run at a constant speed as they would in an ideal design, obtaining an even exposure time depends mainly on being able to make the two curtains accelerate in a similar manner.

When photographing rapidly moving objects, the use of a focal-plane shutter can produce some unexpected effects, since the film closest to the start position of the curtains is exposed earlier than the film closest to the end position. Typically this can result in a moving object leaving a slanting image. The direction of the slant depends on the direction the shutter curtains run in (noting also that as in all cameras the image is inverted and reversed by the lens, i.e. "top-left" is at the bottom right of the sensor as seen by a photographer behind the camera).

Focal-plane shutters are also difficult to synchronise with flash bulbs and electronic flash and it is often only possible to use flash at shutter speeds where the curtain that opens to reveal the film completes its run and the film is fully uncovered, before the second curtain starts to travel and cover it up again. Typically 35mm film SLRs could sync flash at only up to 1/60th second if the camera has horizontal run cloth curtains, and 1/125th if using a vertical run metal shutter.

Film formats

Main article: Film formats

A wide range of film and plate formats has been used by cameras. In the early history plate sizes were often specific for the make and model of camera although there quickly developed some standardisation for the more popular cameras. The introduction of roll film drove the standardisation process still further so that by the 1950s only a few standard roll films were in use. These included 120 film providing 8, 12 or 16 exposures, 220 film providing 16 or 24 exposures, 127 film providing 8 exposures (principally in Brownie cameras) and 35 mm film providing 12, 20 or 36 exposures – or up to 72 exposures in bulk cassettes for the Leica Camera range.

For cine cameras, 35 mm film was the original film format but 16 mm film soon followed, produced by cutting 35 mm in two. An early amateur format was 9.5 mm. Later formats included 8 mm film and Super 8.

Camera accessories

Accessories for cameras are mainly for care, protection, special effects and functions.

  • Lens hood: used on the end of a lens to block the sun or other light source in order to prevent glare and lens flare.

  • Lens cover: covers and protects the lens during storage

  • Lens adapter: sometimes called a step-ring, adapts the lens to other size filters

  • Lens extension tubes allow close focus in macro photography

  • Flash equipment: including light diffuser, mount and stand, reflector, soft box, trigger and cord

  • Care and protection: including camera case and cover, maintenance tools, and screen protector

  • Large format cameras use special equipment which includes magnifier loupe, view finder, angle finder, focusing rail /truck.

  • Battery and charger

Camera designs

Plate camera

The earliest cameras produced in significant numbers used sensitised glass plates and are now termed plate cameras. Light entered a lens mounted on a lens board which was separated from the plate by an extendible bellows. Many of these cameras, had controls to raise or lower the lens and to tilt it forwards or backwards to control perspective. Focussing of these plate cameras was by the use of a ground glassscreen at the point of focus. Because lens design only allowed rather small aperture lenses, the image on the ground glass screen was faint and most photographers had a dark cloth to cover their heads to allow focussing and composition to be carried out more easily. When focus and composition were satisfactory, the ground glass screen was removed and a sensitised plate put in its place protected by a dark slide. To make the exposure, the dark slide was carefully slid out and the shutter opened and then closed and the dark slide replaced. In current designs the plate camera is best represented by the view camera.

Large format camera

Main article: View camera

The large format camera is a direct successor of the early plate cameras and remain in use for high quality photography and for technical, architectural and industrial photography. There are three common types, the monorail camera, the field camera and the press camera. All use large format sheets of film, although there are backs for medium format 120-film available for most systems, and have an extensible bellows with the lens and shutter mounted on a lens plate at the front. These cameras have a wide range of movements allowing very close control of focus and perspective.

Medium format camera

Main article: Medium-format

Medium-format cameras have a film size somewhere in between the large format cameras and the smaller 35mm cameras. Typically these systems use 120- or 220-film. The most common sizes being 6x4.5 cm, 6x6 cm and 6x7 cm. The designs of this kind of camera 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.

Folding camera

The introduction of films enabled the existing designs for plate cameras to be made much smaller and for the base-plate to be hinged so that it could be folded up compressing the bellows. These designs were very compact and small models were dubbed Vest pocket cameras.

Box camera

Main article: Box camera

Box cameras were introduced as a budget level camera and had few if any controls. The original box Brownie models had a small reflex viewfinder mounted on the top of the camera and had no aperture or focusing controls and just a simple shutter. Later models such as theBrownie 127 had larger direct view optical viewfinders together with a curved film path to reduce the impact of deficiencies in the lens.

Rangefinder camera

Main article: Rangefinder camera

As camera and lens technology developed and wide aperture lenses became more common, range-finder cameras were introduced to make focussing more precise. The range finder has two separated 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.

Single-lens reflex

Main article: Single-lens reflex camera

In the single-lens reflex camera the photographer sees the scene through the camera lens. This avoids the problem of parallax which occurs when the viewfinder or viewing lens is separated from the taking lens. Single-lens reflex cameras have been made in several formats including 220/120 taking 8, 12 or 16 photographs on a 120 roll and twice that number of a 220 film. These correspond to 6x9, 6x6 and 6x4.5 respectively (all dimensions in cm). Notable manufacturers of large format SLR include Hasselblad, Mamiya, Bronica and Pentax. However the most common format of SLRs has been 35 mm and subsequently the migration to digital SLRs, using almost identical sized bodies and sometimes using the same lens systems.

Almost all SLR used a front surfaced mirror in the optical path to direct the light from the lens via a viewing screen and pentaprism to the eyepiece. At the time of exposure the mirror flipped up out of the light path before the shutter opened. Some early cameras experimented other methods of providing through the lens viewing including the use of a semi transparent pellicle as in the CanonPellix and others with a small periscope such as in the Corfield Periflex series.

Twin-lens reflex

Main article: 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 focussed using the viewing screen and that under most circumstances the view seen in the viewing screen was identical to that recorded on film. At close distances however, parallax errors were encountered and some cameras also included an indicator to show what part of the composition would be excluded.

Some TLR had interchangeable lenses but as these had to be paired lenses they were relatively heavy and did not provide the range of focal lengths that the SLR could support. Although most TLRs used 120 or 220 film some used 127 film.

Ciné camera

Main article: Movie camera

A ciné camera or movie camera takes a rapid sequence of photographs on strips of film. In contrast to a still camera, which captures a single snapshot at a time, the ciné camera takes a series of images, each called a "frame" through the use of an intermittent mechanism. The frames are later played back in a ciné projector at a specific speed, called the "frame rate" (number of frames per second). While viewing, a person's eyes and brain merge the separate pictures to create the illusion of motion. The first ciné camera was built around 1888 and by 1890 several types were being manufactured. The standard film size for ciné cameras was quickly established as 35mm film and this remains in use to this day. Other professional standard formats include 70 mm film and 16mm film whilst amateurs film makers used 9.5 mm film, 8mm film or Standard 8 and Super 8 before the move into digital format.

The size and complexity of ciné cameras varies greatly depending on the uses required of the camera. Some professional equipment is very large and too heavy to be hand held whilst some amateur cameras were designed to be very small and light for single-handed operation. In the last quarter of the 20th century camcorders supplanted film motion cameras for amateurs. Professional video cameras did the same for professional users around the turn of the century.

Image gallery

Olympus E-420 Four Thirds entry-levelDSLR.

        • 1921 Kodak

        • Opened up Cine Kodak, used 16mm movie film

        • Silvestri Flexicam

        • Voigtländer Brillant twin-lens reflex camera.

        • Contax S of 1949 — the world's first pentaprism SLR

        • 1952 Voigtlander Vito II

        • Asahiflex IIa of 1955

        • Kodak Retina IIIC of 1957

        • Nikon F of 1959 — the first 35mm system camera

        • Voigtländer Vitoret of 1962

        • 1988 A Soviet-era LOMO LC-A camera

        • 2003 — Canon EOS 300D, a model that sparked the popularity of consumer-level DSLRs

A digital camera (or digicam) is a camera that takes video or still photographs, or both, digitally by recording images via an electronicimage sensor. It is the main device used in the field of digital photography. Most 21st century cameras are digital.[1]

Digital cameras can do things film cameras cannot: displaying images on a screen immediately after they are recorded, storing thousands of images on a single small memory device, and deleting images to free storage space. The majority, including most compact cameras, can record moving video with sound as well as still photographs. Some can crop and stitch pictures and perform other elementary image editing. Some have a GPS receiver built in, and can produceGeotagged photographs.

The optical system works the same as in film cameras, typically using a lens with a variablediaphragm to focus light onto an image pickup device. The diaphragm 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. Most digicams, apart from camera phones and a few specialized types, have a standard tripod screw.

Digital cameras are incorporated into many devices ranging from PDAs and mobile phones (calledcamera phones) to vehicles. The Hubble Space Telescope and other astronomical devices are essentially specialized digital cameras.

Types of digital cameras

Digital cameras are made in a wide range of sizes, prices and capabilities. The majority are camera phones, operated as a mobile applicationthrough the cellphone menu. Professional photographers and many amateurs use larger, more expensive digital single-lens reflex cameras(DSLR) for their greater versatility. Between these extremes lie digital compact cameras and bridge digital cameras that "bridge" the gap between amateur and professional cameras. Specialized cameras including multispectral imaging equipment and astrographs continue to serve the scientific, military, medical and other special purposes for which digital photography was invented.

Compact digital cameras

Compact cameras are designed to be tiny and portable and are particularly suitable for casual and "snapshot" uses. Hence, they are also called point-and-shoot cameras. The smallest, generally less than 20 mm thick, are described as subcompacts or "ultra-compacts" and some are nearlycredit card size.

Most, apart from ruggedized or water-resistant models, incorporate a retractable lens assembly allowing a thin camera to have a moderately long focal length and thus fully exploit an image sensor larger than that on a camera phone, and a mechanized lens cap to cover the lens when retracted. The retracted and capped lens is protected from keys, coins and other hard objects, thus making it a thin, pocketable package. Subcompacts commonly have one lug and a shortwrist strap which aids extraction from a pocket, while thicker compacts may have two lugs for attaching a neck strap.

Compact cameras are usually designed to be easy to use, sacrificing advanced features and picture quality for compactness and simplicity; images can usually only be stored using lossy compression (JPEG). Most have a built-in flash usually of low power, sufficient for nearby subjects. Live preview is almost always used to frame the photo. Most have limited motion picture capability. Compacts often have macro capability and zoom lenses but the zoom range is usually less than for bridge and DSLR cameras. Generally a contrast-detect auto focus system, using the image data from the live preview feed of the main imager, focuses the lens.

Typically, these cameras incorporate a nearly silent leaf shutter into their lenses.

For lower cost and smaller size, these cameras typically use image sensors with a diagonal of approximately 6 mm, corresponding to a crop factor around 6. This gives them weaker low-light performance, greater depth of field, generally closer focusing ability, and smaller components than cameras using larger sensors.

Starting in 2011, some compact digital cameras can take 3D still photos. These 3D compact stereo cameras can capture 3D panoramic photos for play back on a 3D TV. Some of these are rugged and waterproof, and some have GPS, compass, barometer and altimeter.

Bridge cameras

Main article: Bridge camera

Bridge are higher-end digital cameras that physically and ergonomically resemble DSLRs and share with them some advanced features, but share with compacts the use of a fixed lens and a small sensor. Like compacts, most use live preview to frame the image. Their autofocus uses the same contrast-detect mechanism, but many bridge cameras have a manual focus mode, in some cases using a separate focus ring, for greater control. They originally "bridged" the gap between affordable point-and-shoot cameras and the then unaffordable earlier digital SLRs.

Due to the combination of big physical size but a small sensor, many of these cameras have very highly specified lenses with large zoom range and fast aperture, partially compensating for the inability to change lenses. On some, the lens qualifies as superzoom. To compensate for the lesser sensitivity of their small sensors, these cameras almost always include an image stabilization system to enable longer handheld exposures.

These cameras are sometimes marketed as and confused with digital SLR cameras since the appearance is similar. Bridge cameras lack the reflex viewing system of DSLRs, are usually fitted with fixed (non-interchangeable) lenses (although some have a lens thread to attach accessory wide-angle or telephoto converters), and can usually take movies with sound. The scene is composed by viewing either the liquid crystal display or the electronic viewfinder (EVF). Most have a longer shutter lag than a true dSLR, but they are capable of good image quality (with sufficient light) while being more compact and lighter than DSLRs. High-end models of this type have comparable resolutions to low and mid-range DSLRs. Many of these cameras can store images in a Raw image format, or processed and JPEG compressed, or both. The majority have a built-in flash similar to those found in DSLRs.

In bright sun, the quality difference between a good compact camera and a digital SLR is minimal but bridgecams are more portable, cost less and have a similar zoom ability to dSLR. Thus a Bridge camera may better suit outdoor daytime activities, except when seeking professional-quality photos.

In low light conditions and/or at ISO equivalents above 800, most bridge cameras (or megazooms) lack in image quality when compared to even entry level DSLRs. However, they do have one major advantage: their much larger depth of field due to the small sensor as compared to a DSLR, allowing larger apertures with shorter exposure times.

A 3D Photo Mode was introduced in 2011, whereby the camera automatically takes a second image from a slightly different perspective and provides a standard .MPO file for stereo display.

Mirrorless interchangeable-lens camera

Main article: Mirrorless interchangeable-lens camera

In late 2008, a new type of camera emerged, combining the larger sensors and interchangeable lenses of DSLRs with the live-preview viewing system of compact cameras, either through an electronic viewfinder or on the rear LCD. These are simpler and more compact than DSLRs due to the removal of the mirror box, and typically emulate the handling and ergonomics of either DSLRs or compacts. The system is used by Micro Four Thirds, borrowing components from the Four Thirds DSLR system.

Front and back of Canon PowerShot A95

Subcompact with lens assembly retracted

Sony DSC-H2