(Digital Single Lens Reflex) A digital still image camera that uses a single lens reflex (SLR) mechanism. Most professional cameras have always been single lens reflex cameras, although analog. Digital SLRs began to emerge in the early 1990s, but became very popular after the turn of the century. Following are the two major differences between DSLRs and standard digital cameras.
Removable Lenses
No single lens can accommodate 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 analog SLRs also fit digital SLRs. However, the CCD or CMOS sensor in a digital SLR is generally not as large as a 35mm film frame, and there is typically a multiplier factor in focal length. For example, using a multiplier factor of 1.5x, a 50mm lens on a 35mm camera is equivalent to a 75mm lens when attached to a digital SLR.
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 an analog SLR). Through-the-lens viewing enables precise manual focusing because tiny LCD screens do not have sufficient resolution. In addition, holding the camera against the face helps steady it.
With the first digital SLRs, the LCD screen was used to review the recorded image, not to preview it for picture taking. In 2006, Olympus introduced the first DSLR with an LCD preview, and other camera vendors followed soon after. See digital camera and Four Thirds system.
Beware the Dust!
Unlike an analog SLR, which uses a completely fresh film frame for each photo, the digital SLR uses the same sensor chip for every image. Unfortunately, that sensor is susceptible to dust, which is why DSLR users are advised to keep a lens on the camera at all times. Starting in 2007, DSLRs began to include a built-in, automatic system for dust reduction or removal.
Cleaning the Sensor
DSLRs have a "mirror lockup" function that flips the mirror out of the way to expose the sensor for cleaning, and there is a raft of sensor cleaning materials on the market that cost from a few dollars to several hundred. For a comprehensive overview of all cleaning methods, visit www.cleaningdigitalcameras.com.
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