A single lens reflex (SLR) camera is a camera with one lens that uses a mirror and prism to reflect the photographic image into the camera’s viewfinder. SLR cameras that store these images on digital cards, instead of imprinting images on film, are known as digital SLRs or DSLRs. Images from these digital cameras can be printed by the user using a personal printer, or by professional photographic developers. Digital images can also be manipulated using various software applications prior to printing.
Sony® created the first prototype DSLR in 1981. Nikon® followed with its version in 1986. Despite these early head starts, it was Kodak® that launched the first commercially available digital camera in 1990. Users took photographs with this camera, which was connected to a storage unit with a cable. This early Kodak® model was priced around $30,000 US Dollars (USD).
In 1999, Nikon’s D1® DSLR gained a foothold in professional photojournalism and sports photography. Manufacturers then focused on supplying affordable digital cameras for the consumer market. Throughout the early 2000s, several companies including FujiFilm®, Cannon®, Nikon®, Minolta (now known as Konica Minolta®), and others introduced their own versions of the consumer DSLR. This led to more options and lower prices for consumers.
Digital camera image quality generally depends on the size of the image sensor, and the number of megapixels used to create the image. The size of the image sensor is more important than the number of megapixels when choosing a DSLR. DSLRs have larger image sensors than typical point-and-shoot digital cameras and, as a result, can take higher quality pictures.
Other advantages include much more creative control through various settings on the DSLR, compared to a point-and-shoot digital camera. Digital SLRs can also use a variety of interchangeable lenses to photograph different events and situations. Since image quality is better, photos can be printed in large formats without losing any resolution.
Digital SLR users will also be faced with some challenges compared to point-and-shoot users. A digital SLR camera is typically much more expensive to purchase and maintain than a more common camera. Digital SLRs are also much more bulky, fragile, and harder to pack and carry when outdoors. Its ability to use different lenses also adds to the amount of equipment the user has to carry.
Photographers who prefer to use a camera in a fully automatic mode may prefer to use a point-and-shoot digital camera. Creative advantages are lost when the user does not want to have to fuss with the different settings and lenses on a DSLR. Also, if photos will be printed using typical, small snapshot formats, DSLR image quality is generally not needed.Source: http://www.wisegeek.com