A digital camera (or digicam for short) is a camera that takes video or still photographs, or both, digitally by recording images via an electronic image sensor.
In the Western market, digital cameras outsell their 35 mm film counterparts.
Digital cameras can do things film cameras cannot: displaying images on a screen immediately after they are recorded, storing thousands of images on asingle small memory device, recording video with sound, and deleting images to free storage space. Some can crop pictures and perform other elementary image editing. Fundamentally they operate in the same manner as film cameras, typically using a lens with a variable diaphragm to focus light onto an image pickup device. The combination of the diaphragm and a shutter mechanism is used to admit thecorrect amount of light to the imager, just as with film; the only difference is that the image pickup device is electronic rather than chemical. Digital cameras are incorporated into many devices ranging from PDAs and mobile phones (called camera phones) to vehicles. The Hubble Space Telescope and other astronomical devices are essentially specialised digital cameras.
Bridge or SLR-like cameras arehigher-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. Autofocus is achieved using the same contrast-detect mechanism, but many bridge cameras feature a manual focus mode for greater control.
Digital singlelens reflex cameras
Main article: Digital single-lens reflex camera
Digital single-lens reflex cameras (DSLRs) are digital cameras based on film single-lens reflex cameras (SLRs). They take their name from their unique viewing system, in which a mirror reflects light from the lens through a separate optical viewfinder. In order to capture an image the mirror is flipped out of the way, allowinglight to fall on the imager. Since no light reaches the imager during framing, autofocus is accomplished using specialized sensors in the mirror box itself. Most 21st century DSLRs also have a "live view" mode that emulates the live preview system of compact cameras, when selected.
These cameras have much larger sensors than the other types, typically 18 mm to 36 mm on the diagonal (crop factor 2,1.6, or 1). This gives them superior low-light performance, less depth of field at a given aperture, and a larger size.
They make use of interchangeable lenses; each major DSLR manufacturer also sells a line of lenses specifically intended to be used on their cameras. This allows the user to select a lens designed for the application at hand: wide-angle, telephoto, low-light, etc. So each lensdoes not require its own shutter, DSLRs use a focal-plane shutter in front of the imager, behind the mirror.
Early developmentThe concept of digitizing images on scanners, and the concept of digitizing video signals, predate the concept of making still pictures by digitizing signals from an array of discrete sensor elements. Eugene F. Lally of the Jet Propulsion Laboratory described amosaic photosensor for use as a star sensor for measuring the altitude of a spacecraft at a 1961 space conference. At Philips Labs. in NY Edward Stupp, Pieter Cath and Zsolt Szilagyi filed for a patent on "All Solid State Radiation Imagers" on Sept. 6, 1968 and constructed a flat screen target for receiving and storing an optical image on a matrix composed of an array of photodiodes connected to acapacitor to form an array of two terminal devices connected in rows and columns. Their US patent was granted on Nov. 10, 1970. Texas Instruments engineer Willis Adcock designed a filmless camera that was not digital and applied for a patent in 1972, but it is not known whether it was ever built. The first recorded attempt at building a digital camera was in 1975 by Steven Sasson, an...
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