- This article is about the subject of this wiki. For other uses, see Camera (disambiguation).
|image by Mike Overs (Image rights)|
A camera is a hollow space with an opening admitting light. When used, it contains some image recording media, fixed in the plane where the refractive power of a lens projects an image (or, in the simplest case, just a pinhole). The aperture is aimed in the direction of some scene or subject, and the opening uncovered for a duration suitable to the recording medium. The variations on this theme are endless.
At this point film cameras and digital cameras must be distinguished. The former use film as a medium. A digital camera needs some electronics aboard, a sensor chip, a power supply, an image processor and electronic storage media to save captured images.
Common elements of most cameras are a lens, some focusing facility, a lens diaphragm, a shutter, film advance facilities, a viewfinder, exposure and distance measuring facilities, and perhaps electronic features like switches and LCD displays.
Camera is an abbreviation of camera obscura (Latin for dark chamber), mainly known as a facility for landscape artists in the 18th century. The camera obscura had a lens/mirror optics as light opening, the "media" in the camera was the painter who traced with his pencil the contours of the image projected onto his white paper sheet. Or the camera was a wooden box with lens and a screen onto which the image was projected. The painter could lay transparent paper onto the screen to draw a sketch. The abbreviated term camera caught on with the spreading of photochemical imaging around 1840. Some of the early photographic cameras were derived from the wooden box types of the camera obscura.
Anatomy of a Camera
The camera or "dark chamber" is basic part of a camera. In most cases its light opening is positioned opposite to the image plane where the light-sensitive medium is placed for exposure inside the chamber.
A camera has at least a little round hole (pinhole) to let in light. Better imaging results are achieved by designing that opening a little larger and mounting a lens into it. Then the lens is the camera's light opening. The lens can be part of the camera, or it is accessory for camera systems with exchangeable lenses.
The shutter is the mechanism that opens for a specified interval and closes in order to allow light to pass through the lens (or through the hole of a pinhole camera) onto the image recording medium. The four most common types of shutter are guillotine shutter, rotary shutter, leaf shutter and focal plane shutter. In the early days of photography exposure times had been so long that cameras needed no other shutter than the lens cover.
The light-sensitive medium to be exposed to light is contained inside the camera, with the part of medium to be used for the next exposure exactly positioned in the image plane. Film combines light sensitivity with image storage. Film cameras may include a film-load/film-advance system; very old simpler film cameras as well as big professional studio film cameras must be loaded with a new unexposed film sheet for every exposure.
In digital cameras, the light-sensitivity and storage are separate. Light-sensitivity is provided by some kind of sensor, such as a CCD or CMOS type, connected to a digital data storage device. While spinning media such as floppy disks, CD-Rs or miniature hard disks were used in early cameras, they have been superseded by solid-state flash memory in contemporary models. Digital cameras typically allow the exchange of memory cards (or disk media). Digital cameras without exchangeable media must have an electronic interface to make image data accessible.
The light opening must be the only spot where light enters a camera when it is actually used for imaging. Otherwise images would be spoiled. Nearly all film cameras and many digital cameras have shutters which keep any light away from the media except at the moment of exposure. Film especially must be protected from any further light, before exposure as well as afterwards, until it is developed and fixed chemically in the photo laboratory.
The part of film or the photographic glass plate to be exposed next is usually in a fixed position. The glass plates need the frame to be fixed, the film rolls need a frame that delimits the area on the film to be used for one exposure. The part of film to be exposed next lies stretched directly in the frame, positioned exactly in the image plane. In many digital cameras the sensors are also mounted in a frame, but the "frame size" of a digicam is the effective size of the rectangular image area on the sensor chip. The position of the image sensor is not necessarily fixed when it's mounted on an anti-shake mechanism that corrects the position of the image plane during exposure.
Some cameras - especially medium format and large format cameras - have interchangeable backs. Some backs allow continuous shooting on very long film rolls, or with film plate magazines. Backs also make it possible to use different film formats. Some cameras have backs available for everything from 35mm to 6x6 to 8x10 film or digital sensor. Some cameras give the choice of using the internal film load system or that of an alternate camera back or even an alternate digital back with sensor and memory instead of film.
View cameras need to be focussed and composed with a ground glass screen, which is exchanged for the film back each separate exposure.
A few film camera backs - "Data Backs" - could print information onto each frame, such as the date/time of the exposure and the frame number.
An elongatable box camera (sliding box camera) or a view camera with movable back allow focusing without changing the position of the lens or single lens elements. Other cameras may be focusable by moving the lens or just a certain group of its lens elements for- and backward, or by adding lens elements. A meter or feet scale might indicate the chosen image subject distance. Visual-control of correct focusing can be aided by ground glass, rangefinder, or the matte screen in the viewfinders of SLR and TLR cameras.
The viewfinder is the part of the camera that indicates, either optically or electronically, what will appear in the field of view of the lens. In most cases this is an optical device to look through to compose, but in some cases in can be as simple as one or more wire frames you use to approximate your field of view. Many of today's point-and-shoot digicams have omitted the optical viewfinder and use an LCD screen on the back of the camera as its viewfinder.
A diopter adjustment is an optical adjustment on the viewfinder of a camera that allows someone to adjust the viewfinder's magnification to their vision, removing the need to wear eyeglasses when looking through it. Diopter adjustments cannot compensate for all vision problems, only near and far sightedness can be compensated.
Film load and advance
Most film cameras feature a more or less elaborate film load and advance system. That can be a sophisticated film plate exchange system of a magazine camera, an easy-to-load rollfilm chamber, a fast single-stroke film-advance lever, a smart advance mechanism for a film cassette system, an electric fully automatic load-, advance- and rewind-system for a capsuled film type, or whatever is imaginable.
A frame counter or exposure counter is a mechanism for recording the number of film frames exposed or for calculating the number of exposures remaining on a roll of film or memory card.
Modern Camera features
A light meter may be built into a camera. In digital cameras the image sensor might serve as light meter too.
Cameras with auto-exposure are able to set the shutter speed, the aperture, or both automatically based on the meter reading.
TTL or through the lens metering is a method of metering in which a camera's built-in light meter reads the light coming through the lens. This is considered to be more accurate because the light meter only sees the light that will hit the focal plane and other ambient light conditions can't "fool" the meter.
Center-weighted light-meters favor the center of the frame, while taking into account the rest of the frame to a lesser extent.
Autofocus cameras are able to adjust the lens electronically in order to get your desired subject "in focus". See autofocus.
Automatic image correction
Automatic image corrections are special features of some digital cameras.