DSLR
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A digital single lens reflex or DSLR camera is a single-lens reflex camera (SLR) which records images using electronic sensor instead of film. Like SLRs, DSLRs are often used by professional photographers and advanced amateurs.
DSLR accepts interchangeable lenses and accessories such as flash units, and accessories for SLRs are usually compatible with DSLRs of the same brand. When aiming a DSLR, the photographer is looking through the lens (unlike a rangefinder camera or a camera with a separate viewfinder) and the image is projected optically (unlike a camera with an electronic viewfinder).
The imaging sensor in a DSLR is typically much larger than the one in a standard digital camera. Larger sensor allows better image quality, shallower depth of field and wider field of view. However, the sensor is usually smaller than a frame of 135 film. The average size of a typical DSLR sensor being about 22mm x 15mm, or the size of an APS film frame. If this is not the case and the sensor is the same size as the equivalent frame of film (usually 35 mm wide), the camera is said to have a full-frame sensor. Currently (2005) only some expensive professional DSLRs have full-frame sensors (typically 36mm x 24mm). One example of a full-frame DSLR is the Canon EOS-1Ds Mark II.
Depending on the position of the reflex mirror, the light from the scene can only reach either the eyepiece or the sensor. Also, a mechanical shutter is used to control the exposure. Therefore even though a DSLR has a color display at the back of the camera body, it doesn't provide "live preview" (allowing focusing and framing using the display). The only exception to this rule so far is Canon EOS 20Da, a Japanese variant of Canon EOS 20D designed for astrophotography.
Camera manufacturers expect that professionals and advanced amateurs continue to prefer DSLRs over other forms of digitals cameras. However, if electronic viewfinders with near-zero lag and very low energy consumption are introduced, non-SLR cameras may become a viable choice for a large number of people who now need SLRs.
Many medium format SLRs can accept a digital camera back to turn the camera into a kind of DSLR with very high image quality. However, the combination is very expensive and bulky, and thus they are rarely used outside fashion photography and portraiture.