The camera is a tool that controls the transmission of light or other energy
that is required to create a visual record using light-sensitive materials or
digital sensors. The energy from a scene is transmitted into a dark chamber by
an opening in one end, which allows light from the scene within the angle of
coverage of the lens to enter the camera. The light going through the opening
will form an inverted image on the opposite side of the unit where a film or
other receptor will record the image. The amount of the light is controlled by
the size of the opening in the camera or lens and the length of time the opening
is left uncovered.
A typical still camera takes one photo each time the user presses the
shutter button. A typical movie camera continuously takes 24 film frames per second as long as the user holds down the shutter button.
History of the camera
The forerunner to the camera was the
camera obscura. The camera obscura is an instrument consisting of a darkened chamber or box, into which light is admitted through a convex lens, forming an image of external objects on a surface of paper or glass, etc., placed at the focus of the lens. The camera obscura was first invented by the Iraqi scientist Ibn al-Haytham (Alhazen) as described in his Book of Optics (1015-1021). Irish scientist Robert Boyle and his assistant Robert Hooke later developed a portable camera obscura in the 1660s.
The first camera that was small and portable enough to be practical for
photography was built by Johann Zahn in 1685, though it would be almost 150 years before technology caught up to the point where this was practical. Early photographic cameras were essentially similar to Zahn's model, though usually with the addition of sliding boxes for focusing. Before each exposure, a sensitized plate would be inserted in front of the viewing screen to record the image. Jacques Daguerre's popular daguerreotype process utilized copper plates, while the calotype process invented by William Fox Talbot recorded images on paper.
The first permanent color photograph, taken by James Clerk Maxwell in 1861.
The first permanent photograph was made in 1826 by Joseph Nicéphore Niépce using a sliding wooden box camera made by Charles and Vincent Chevalier in Paris. Niépce built on a discovery by Johann Heinrich Schultz (1724): a silver and chalk mixture darkens under exposure to light. However, while this was the birth of photography, the camera itself can be traced back much further. Before the invention of photography, there was no way to preserve the images produced by these cameras apart from manually tracing them.
The development of the collodion wet plate process by Frederick Scott Archer in 1850 cut exposure times dramatically, but required photographers to prepare and develop their glass plates on the spot, usually in a mobile darkroom. Despite their complexity, the wet-plate ambrotype and tintype processes were in widespread use in the latter half of the 19th century. Wet plate cameras were little different from previous designs, though there were some models, such as the sophisticated Dubroni of 1864, where the sensitizing and developing of the plates could be carried out inside the camera itself rather than in a separate darkroom. Other cameras were fitted with multiple lenses for making cartes de visite. It was during the wet plate era that the use of
bellows for focusing became widespread.
The first color photograph was made by Scottish physicist James Clerk Maxwell, with the help of English inventor and photographer Thomas Sutton, in 1861
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19th century studio camera, with bellows for focusing.
Traditional cameras capture light onto
photographic film or photographic plate. Video and
digital cameras use electronics, usually a charge coupled device
(CCD) or sometimes a CMOS sensor to capture images which can be transferred or stored in tape or computer memory inside the camera for later playback or processing.
Cameras that capture many images in sequence are known as
movie cameras or as ciné cameras in Europe; those designed for single images are still cameras. However these categories overlap. As
still cameras are often used to capture moving images in special effects work and modern
digital cameras are often able to trivially switch between still and motion recording modes. A
video camera is a category of movie camera that captures images electronically (either using analogue or digital technology).
Auto-focus systems can capture a subject a variety of ways; here, the focus is on the person's image in the mirror.
Due to the optical properties of
photographic lenses, only objects within a limited range of distances from the camera will be reproduced clearly. The process of adjusting this range is known as changing the camera's focus. There are various ways of focusing a camera accurately. The simplest cameras have fixed focus and use a small
aperture and wide-angle lens to ensure that everything within a certain range of distance from the lens, usually around 3 metres (10 ft) to infinity, is in reasonable focus. Fixed focus cameras are usually inexpensive types, such as single-use cameras. The camera can also have a limited focusing range or scale-focus that is indicated on the camera body. The user will guess or calculate the distance to the subject and adjust the focus accordingly. On some cameras this is indicated by symbols (head-and-shoulders; two people standing upright; one tree; mountains).
Rangefinder cameras allow the distance to objects to be measured by means of a coupled parallax unit on top of the camera, allowing the focus to be set with accuracy.
Single-lens reflex cameras allow the photographer to determine the focus and composition visually using the objective lens and a moving mirror to project the image onto a ground glass or plastic micro-prism screen.
Twin-lens reflex cameras use an objective lens and a focusing lens unit (usually identical to the objective lens.) in a parallel body for composition and focusing.
View cameras use a ground glass screen which is removed and replaced by either a photographic plate or a reusable holder containing sheet film before exposure. Modern cameras often offer autofocus systems to focus the camera automatically by a variety of methods e.g. by fishing.
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.