Digital single-lens reflex camera
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A digital single-lens reflex camera (digital SLR or DSLR) is a digital camera that operates on the same optical and mechanical principles as a modern electronic autofocus 35mm film single-lens reflex camera. The key difference is that the film is replaced with a CCD or CMOS image sensor plus accompanying electronics, thus creating images digitally in-camera, without the need to first chemically develop a latent image on film.
SLR design
The single-lens reflex (SLR) camera uses a mirror to show the image that will be captured in a viewfinder. The cross-section (side-view) of the optical components of an SLR shows how the light passes through the lens assembly (1), is reflected by the mirror (2) and is projected on the matte focusing screen (5). Via a condensing lens (6) and internal reflections in the roof pentaprism (7) the image appears in the eyepiece (8). When an image is taken, the mirror moves in the direction of the arrow, the focal-plane shutter (3) opens, and the image is projected in the sensor (4) in exactly the same manner as on the focusing screen.
DSLR properties and advantages are described in the following subsections:
Parallax-free optical viewfinder
The principal advantage of DSLR cameras over other digital cameras is the defining characteristic of an SLR: the parallax-free lag-free optical viewfinder.
The advantage of seeing the image exactly as it will be captured, through the taking lens, without parallax errors due to a viewfinder offset from the lens, has been duplicated electronically in many digital compact cameras having a live LCD. However, since these electronic viewfinders are not optical, they can not duplicate the zero lag of an optical viewfinder, and have quite low resolution making it hard to see details and are sometimes hard to make bright enough for outdoor use.
Fast phase-detection autofocus
Like most film SLRs, DSLRs typically use a phase detection autofocus system. This method of focus is very fast, but requires the insertion of a special sensor into the optical path, so it is usually only used in SLR designs. Compact cameras that use the main sensor to create a live preview on the LCD or electronic viewfinder need to use the slower contrast method of autofocus.
Interchangeable lenses
The ability to exchange lenses, to select the best lens for the current photographic need, and to allow the attachment of specialized lenses, is a key to the popularity of DSLR cameras, though not inherently unique to DSLRs.
In the digital era, zoom lens design is sufficiently advanced to almost eliminate most of the market for non-SLR cameras with interchangeable lenses, so digital camera lens interchangability is, in practice, mostly restricted to the digital SLR. A non-SLR camera can have a fixed lens which will zoom from medium wide-angle to medium telephoto, omitting only fish-eye and extreme telephoto. However, there are at least four advanced digital non-SLR cameras with interchangeable lenses (see "Compacts" below).
Sensor quality
The image sensor in a DSLR is typically much larger than the one in a consumer-level, compact digital camera. A larger sensor allows better image quality, lower noise, shallower depth of field and higher sensitivity with same noise. Many DSLR sensors are roughly APS-sized, i.e., approximately 22 mm x 15 mm, a little smaller than the size of an APS-C film frame, much smaller than a frame of 135 film. A high-end compact camera like the Nikon Coolpix 8800 has an 8.8 by 6.6 mm sensor (2/3 inches format), about 4 to 6 times smaller area than a typical DSLR sensor, lower end digital compacts have even smaller sensors.
Depth-of-field control
The larger size of the sensor of the DSLRs compared to compact digitals makes it much easier to limit the depth of field, for example to emphasise a face by blurring the background so that the viewer will not get distracted by the details in the background.
Angle of view
The angle of view of a lens depends upon its focal length and the image size; a sensor smaller than 35mm film means that a lens of given focal length will have a narrower angle of view than it would on 35mm film. If the sensor is the same size as the equivalent frame of film (36 mm x 24 mm), the camera is said to have a full-frame sensor. As of 2006, only a few DSLRs have full-frame sensors (currently in production the Canon EOS-1Ds Mark II and the Canon EOS 5D ). Medium-format size sensors, as used on the Mamiya ZD and other cameras, are even larger than 35mm or full-frame sensors, and capable of even greater image quality, but are much more expensive.
The impact of sensor size on field of view is referred to as the "crop factor" or "focal length multiplier", which is a factor by which a lens focal length can be multiplied to give the full-frame-eqivalent focal length for a lens. Roughly APS-sized sensors have a crop factor of 1.5 or 1.6, so a lens with a focal length of 50mm will give a FOV equal to that of a 75mm or 80mm lens on a full-frame camera. This crop makes achieving long telephoto images on an APS-sensor camera much easier than on a full-frame camera; though wide-angle views suffer by the same amount. Shallow depth-of-field images also tend to be more limited, since the wider the lens you use the more depth-of-field you get, so the smaller the sensor the more depth-of-field with the same aperature and field of view.
Alternatives to the 35mm-based DSLR
Depending on the position of the reflex mirror, the light from the scene can only reach either the viewfinder or the sensor. Also, a mechanical diaphragm is used to control the exposure. Therefore, most DSLRs don't provide "live preview" (allowing focusing, framing, and depth-of-field preview using the display). As of April 2006, there are two notable exceptions: the Olympus E-330 and the Panasonic Lumix DMC-L1 (available sometime in 2006) — both of which are Four Thirds System cameras.
Many medium format roll-film SLRs can accept a digital camera back to turn the camera into a DSLR with very high image resolution and quality (typically 22 megapixel as of 2005). However, the combination is very expensive and bulky, and more suited to the studio than an outdoor environment.
DSLRs dominate the high end of the digital camera market. However, if electronic viewfinders with near-zero lag time, increased reliability, very low power consumption, and good brightness are introduced, and if a good fast AF mechanism that is compatible with using the main sensor for viewing is developed, then non-SLR cameras may become a viable alternative for a large number of people who now use SLRs.
History
At Fotokina in 1986, Nikon revealed a prototype analog electronic still SLR camera, the Nikon SVC, a precursor to the digital SLR [Nikon SLR-type digital cameras], Pierre Jarleton. The prototype design lead to the Nikon N8008 two years later which is capable of 0.3 megapixel.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 camera was capable of producing 1.3 megapixel (1280x1024) and cost approximately $30,000 US. This was followed by the DCS-200 with integrated storage.[A brief info on Kodak DCS-Series Digital Still SLR cameras], Photography in Malaysia
Over the next decade, digital SLRs have been released by various companies such as Canon, Nikon, Kodak, Pentax, Olympus, Konica Minolta, Fujifilm, and Sigma with higher resolution and lower prices.
In January 2000, Fujifilm announced the finepix S1-pro which was the first DSLR that had a 'resonable' price and was marketed to non-professionals.
In 2003, Canon introduced a 6.3 megapixel Digital Rebel SLR camera (known in the UK as the EOS 300D) at an MSRP of under $1000. Its popularity, especially among newspaper and amateur photographers, encouraged other manufacturers to produce affordable digital SLR cameras, significantly lowering entry costs and allowing more casual photographers an opportunity to experience the digital SLR photography. Canon introduced the next generation 8 megapixel EOS350D (Digital Rebel XT) in 2005.
In February 2004, Kodak released two 14-megapixel full-frame (24x36mm) DLSRs named Kodak DCS 14 N and DSC 14 C, one for Nikon lens mount and one for Canon lens mount. These cameras were expensive, and not very sensitive, and Kodak has since discontinued them. Konica Minolta briefly produced two DSLR models, the 5D and 7D, but has sold their digital camera business to Sony which revamped the range through its alpha brand. At one time, Kyocera also manufactured DSLRs and marketed them under the Contax name,[Contax N Digital], world's first digital SLR camera with full-frame 24 x 36mm 6 megapixel CCD, Kyocera press release, 08 october 2002 but in 2005 withdrew from the DSLR camera field. Sigma produced the SD9 and SD10 DSLR cameras with the Foveon X3 sensor, but those cameras are no longer in production; a successor has been promised but not yet announced.
Canon, Nikon, Pentax, Olympus, Sony and Fujifilm currently have DSLR models in production.
Present day
Canon and Nikon currently have the largest range of amateur and professional DSLR cameras. Canon's line includes the 350D, 30D, 5D, 1D Mk. IIn and the 1Ds Mk. II. Nikon also has a broad line of DSLRs which includes the D50, D70, D70s, D200, D2Hs and D2X. Fujifilm sells a Nikon-lens compatible DSLR. Olympus has introduced four DSLR models of its own design, including the E-330, first real DSLR with a live preview LCD in addition to the viewfinder. Sigma produces an innovative DSLR with the multi-layered Foveon X3 sensor to deliver excellent color and detail, while Pentax also has digital SLRs that use their lenses and accessories. Hasselblad and Mamiya produce medium-format DSLRs which produce the highest quality digital images. Their larger sensors are able to capture much more detail than the 35mm full-frame and smaller sensors found on the Canon, Nikon, Olympus, Pentax, and Sigma models.Digital SLR versus SLR-like and compact cameras
Non-SLR digital cameras are of two types: SLR-like "prosumer" cameras with permanently fixed zoom lenses, and digital compacts cameras.SLR-like cameras
The "SLR-like" cameras (e.g. some Nikon Coolpix models, the Sony DSC H and R series, the Panasonic FZ series, the Canon PowerShot S and Pro models, and several Fujifilm FinePix models) offer TTL viewing through the focusing lens, projected onto its viewfinder as well as a LCD screen, through an EVF (electronic viewfinder). The difference compared to a DSLR is that the viewfinder shows a digitally created copy of the TTL image whereas the viewfinder in a DSLR shows the real optical TTL image via its mirror. An EVF image reacts slower to view changes and has a lower resolution than an optical viewfinder, but achieves parallax-free viewing using less bulk and mechanical complexity than a DSLR with its reflex viewing system. The limitation of a prosumer digital camera is, of course, its fixed lens, typically limited to about a 10:1 focal length range. Also, the fixed lens minimizes the risk of getting dust on the sensor.Several of the high-end prosumer cameras have a moveable LCD screen (e.g. Canon PowerShot Pro1), which can be used instead of the regular viewfinder in difficult angles, enabling the photographer to look through the lens even when standing above or below the camera. The LCD screen also enables the photographer to look at the stored pictures in a convenient way.
Compacts
The compact digital cameras can usually be operated at arm's length using only the LCD display screen at the rear of the camera, and most models also have simple optical viewfinders like traditional compact film cameras. Like the SLR-like prosumer cameras, nearly all compacts have no ability to accept interchangeable lenses, with the exception of the Epson R-D1.Most compacts are therefore provided with a zoom lens that covers the most commonly used focal lengths. Compacts may be altered through the use of supplementary add-on lens converters to provide an added telephoto or wide angle field of view, though the image quality is usually affected to a significant degree. Most compacts are significantly slower in shutter speed capture (time from image capture to sensor and storage) than DSLR cameras, a disadvantage for action, wildlife, and sports photography. Their zoom lenses can frequently have a much slower (smaller) effective wide-open aperture (f-stop) than DSLR or prosumer cameras, especially at the telephoto end, which further limits their utility in situations involving low light levels and moving subjects.
See also
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