A digital single-lens reflex camera (digital SLR or DSLR) is a digital camera that uses a mechanical mirror system and pentaprism to direct light from the lens to an optical viewfinder on the back of the camera.
The basic operation of a DSLR is as follows: for viewing purposes, the mirror reflects the light coming through the attached lens upwards at a 90 degree angle. It is then reflected twice by the pentaprism, rectifying it for the photographer’s eye. During exposure, the mirror assembly swings upward, the aperture narrows (if stopped down, or set smaller than wide open), and a shutter opens, allowing the lens to project light onto the image sensor. A second shutter then covers the sensor, ending the exposure, and the mirror lowers while the shutter resets. The period that the mirror is flipped up is referred to as “viewfinder blackout”. A fast-acting mirror and shutter is preferred so as to not delay an action photo.
All of this happens automatically over a period of milliseconds, with cameras designed to do this 3–10 times a second.
DSLRs are often preferred by professional still photographers because they allow an accurate preview of framing close to the moment of exposure, and because DSLRs allow the user to choose from a variety of interchangeable lenses. Most DSLRs also have a function that allows accurate preview of depth of field.
Many professionals also prefer DSLRs for their larger sensors compared to most compact digitals. DSLRs have sensors which are generally closer in size to the traditional film formats that many current professionals started out using. These large sensors allow for similar depths of field and picture angle to film formats.
The term DSLR generally refers to cameras that resemble 35 mm format cameras, although some medium format cameras are technically DSLRs.
History:-
On August 25, 1981 Sony unveiled a prototype of the first still video camera, the Sony Mavica. This camera was an analog electronic camera that featured interchangeable lenses and a SLR viewfinder.
At Photokina in 1986, Nikon revealed a prototype analog electronic still SLR camera, the Nikon SVC, a precursor to the digital SLR.[25] The prototype body shared many features with the N8008.[25]
In 1991, Kodak released the first commercially available digital SLR, the Kodak DCS-100. It consisted of a modified Nikon F3 SLR body, modified drive unit, and an external storage unit connected via cable. The 1.3 megapixel camera cost approximately US$30,000. This was followed by the Kodak DCS-200 with integrated storage.[26]
Over the next decade, DSLRs have been released by various companies, including Canon, Nikon, Kodak, Pentax, Olympus, Panasonic,Samsung, Minolta (later Konica Minolta, and whose camera assets were then acquired by Sony), Fujifilm, and Sigma, with higher resolutions and lower prices.
In 1999, Nikon announced the Nikon D1, the first DSLR to truly compete with, and begin to replace, film cameras in the professional photojournalism and sports photography fields. This camera was able to use current autofocus Nikkor lenses available at that time for the Nikon film series cameras, and was also able to utilize the older Nikon and similar, independent mount lenses designed for those cameras. A combination of price, speed, and image quality was the beginning of the end of 35 mm film for these markets.
In January 2000, Fujifilm announced the FinePix S1 Pro, the first DSLR marketed to non-professionals.
In November 2001, Canon released its 4.1 megapixel EOS-1D, the brand’s first professional digital body.
In 2003, Canon introduced the 6.3 megapixel EOS 300D SLR camera (known in the United States as the Digital Rebel and in Japan as the Kiss Digital) with an MSRP of US$999, directed at the consumer market. Its popularity encouraged other manufacturers to produce affordable digital SLR cameras, lowering entry costs and allowing more amateur photographers to purchase DSLRs.
Since 2003, the number of megapixels in imaging sensors have increased steadily, with most companies focusing on build quality, high ISO performance, speed of focus, higher frame rates, the elimination of digital ‘noise’ produced by the imaging sensor, and price reductions to lure new customers.
