A CDE Definition
(Digital Single Lens Reflex) A digital still image camera that uses a single lens reflex (SLR) mechanism. Most professional cameras have been single lens reflex, although analog film until digital SLRs emerged in the early 1990s. Following are the two major differences between DSLRs and standard digital cameras.
No single lens can handle every photographic requirement, and SLR cameras have always used removable lenses. A wide variety of lenses are available for each camera system, and many lenses that fit 35mm film SLRs also fit digital SLRs. However, the CCD or CMOS sensor in all but high-end digital SLRs is generally not as large as a 35mm frame, and 35mm lenses produce different focal lengths (see crop factor). See CCD sensor and CMOS sensor.
Through the Lens
In an SLR, the photographer sees the image through the actual picture lens. To compose the picture, a mirror reflects the light from the lens to the viewfinder. When the picture is taken, the mirror momentarily flips out of the way to allow the light to pass through the lens diaphragm to the CCD or CMOS sensor (or to film in analog SLRs). Through-the-lens viewing enables precise manual focusing because tiny LCD screens do not have sufficient resolution. In addition, holding the viewfinder against the face helps steady it.
The LCD screen in early DSLRs was used to review the recorded image, not to preview the picture before shooting. In 2006, Olympus introduced the first DSLR with a "live preview LCD," and other camera vendors followed. See mirrorless camera, viewfinder, digital camera and Four Thirds system.
Beware the Dust!Unlike an analog SLR, which uses a fresh film frame for each photo, the digital SLR uses the same sensor chip forever. Since the sensor is susceptible to dust, it is imperative to always keep the lens port covered. Starting in 2007, DSLRs began to include automatic dust removal.
A "mirror lockup" function flips the mirror out of the way to expose the sensor for cleaning, and there is a raft of cleaning materials on the market. For a comprehensive overview, visit www.cleaningdigitalcameras.com.
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