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A digital single-lens reflex camera ('''digital SLR''' or '''D-SLR''') 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. Parallax-free optical viewfinder The principal advantage of D-SLR cameras over other digital cameras is the defining characteristic of an SLR: the image in the optical viewfinder is Parallax -free, because its light is routed directly from the main lens itself, rather than from an off-axis viewfinder. This advantage of seeing the image as it will be captured has been duplicated in many compact digital cameras (referred to typically as ''digicams'') in their LCD displays; however, the SLR still retains an advantage because the LCD images are electronically mediated and thus exhibit time lag, and also have relatively low resolution and brightness making it difficult to see details, especially in outdoor use. In contrast, the SLR's optical image is in real-time and is brighter and more detailed. Some SLR's and D-SLR's will have a brighter image because the pentaprism is composed of optical glass instead of the newer, penta-mirror found on less-expensive cameras. The penta-mirror design is composed mostly of plastic and is cheaper for the manufacturer to produce. Another factor in brightness will be the camera's focusing. On some film SLR's, notably the Nikon F, F2, F3, F4, F5 and the current F6 35mm models, the focusing screen is interchangeable. In rare cases, such as the Nikon D200, the focusing screen can be exchanged via Nikon Service Technicians for a fee. Third-party manufacturers such as Beattie, manufactured what was referred to as the "Beattie Intenscreen®" and these interchanged with the manufacturers' focusing screen to produce a brighter image in the viewfinder. (See Fast phase-detection autofocus Like most film SLR s, D-SLRs typically use a phase detection Autofocus system. This method of focus is very fast, and results in less focus "searching", but requires the insertion of a special sensor into the optical path, so it is usually only used in SLR designs. Digicams 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 D-SLR cameras. This feature is also shared by certain Rangefinder Cameras , both film and digital in operation. Two such digital rangefinders are the Epson R-D1 (possibly discontinued) and the Leica M8 . However, both of these rangefinder camera models lose one feature that previous Leica and other rangefinder users have long desired - the ability to use the full lens coverage of wide-angle lenses. For example, the 20mm lenses for these cameras, covering an approximate diagonal coverage of 94 degrees, have their diagonal angle of view further restricted by the DX-sized sensor incorporated into their designs. Thus a 20mm lens angle of view is changed (by a factor of approximately 1.5) to that of a 30mm lens. A Leica photographer, for example, desiring the full use of his wide-angle lenses, will probably opt for a film-based Leica and then have a photo-lab scan his negatives and/or transparencies (slides) into digital format. , right, which converts 35mm film images to digital]] Mount compatibility across camera generations The Nikon F-mount lens systems and the Pentax K-mount systems are the only 35mm SLR camera systems (apart from the Leica M-mount rangefinder system) that allow the photographer to use a mechanical SLR camera body, a fully automatic SLR camera body, and a D-SLR camera body, all utilizing the same lenses. Thus, if a photographer is working in extreme climate conditions (i.e., the top of a high mountain where the temperatures are below freezing), that photographer can change from a digital camera body, which is totally dependent upon battery-power, to a mechanical film camera body, which has no battery or power limitations, and continue photographing. The only aspects of these manufacturers' lenses which have changed are the addition of electronic contacts, autofocus abilities and, in some cases, the elimination of the external aperture ring for electronic control (i.e., Nikon's 'G-type' autonikkors, which cannot be used on a mechanical SLR camera body). Conversely, while Canon, Olympus and certain other manufacturers have produced good 35mm film camera bodies, neither Canon's EOS 35mm camera bodies nor Olympus four-third system camera bodies are mechanical, since both manufacturers abandoned their respective lens mounts designed for 35mm film cameras (i.e., the Canon FD lens mount was abandoned in the 1980's for the EOS lens mount, which is heavily electronic; and the Olympus MD lens mount for the OM series cameras was abandoned for the four-thirds lens mount). The four-thirds lens mount system is currently shared by Leica, Panasonic and Olympus. Scanning methods There are currently three ways to scan or convert an image to digital format. The first is through a desktop scanner which, depending upon the model used, can scan a paper sized image from 8" x 14" to ledger size, 11" x 17". The second method is through the use of a dedicated film scanner such as this Nikon Coolscan (pictured) which can scan 35mm transparencies and negatives. Other Nikon scanners can scan a larger size negative up to 6 cm. x 7 cm. The third method is to simply mount a digital camera on a copy stand (or an old enlarger with its projection head removed) and photograph the object or image to be converted to digital format. Digicams and lens usage Some digicams such as the Canon PowerShot G7 and the Canon PowerShot S5-IS, offer optional converter lenses that attach to the front-end of their fixed lenses in order to mimic the ability to use multiple lenses. However, these lenses have to be specifically designed for the host cameras in order to minimize the loss of resolution. Some third-party manufacturers such as Century manufacture front lens converters for both digicams and video cameras. The front diameters of the lenses for D-SLRs are generally larger than for digicams. The reason for this is that the sensor size for D-SLR's is larger, specifically, it's referred to as 'DX format'. To cover the larger DX format or full-frame format, a lens needs greater covering power. These cameras, which generally have faster lenses (some have interchangeable lenses with 'fast' f/2.8 apertures and faster) record more detail and allow more light to the sensor. The result is that the camera gives the photographer the option of using higher ISO speeds because these DX chips have less of a noise factor, and they allow the photographer to use faster shutter speeds, especially in the case of low light or moving subjects. Zoom lenses and lens design in general In discussing 35mm SLR and D-SLR cameras and zoom lens designs, zoom lenses were originally designed with a fixed aperture. Because early SLR's had no built-in light meters, exposure was calculated using a hand-held meter such as a Gossen, Sekonic, Weston or other such hand-held light meter designed for photography. With the advent first, of through the lens metering, then with the introduction of shutter and aperture priority automation, and finally autofocus introduced with the 35mm SLR Minolta Maxxum camera system, lens designers were then free to introduce some zoom lenses with variable apertures (i.e. the f/number becomes smaller as the photographer zooms the lens to the telephoto setting), which were easier to manufacture and sell. However there is still a demand for fixed aperture zoom lenses among professional and advanced photographers. In the digital era, Zoom Lens design is sufficiently advanced to almost eliminate fixed focal length lenses since these zoom lenses are sufficiently sharp. Non-SLR cameras with interchangeable lenses are few in number, being used only by advanced amateur and professional photographers. These cameras would probably be high-end rangefinder cameras with fast lenses and would be used for theater photography or other situations in low light where the photographer doesn't want to be intrusive by using an electronic flash or other lighting unit. Thus, digital camera lens interchangeability is mostly restricted to the D-SLR. Digicams (non-SLR and D-SLR) have a fixed (non-interchangeable) lens which will zoom from medium wide-angle to medium telephoto, omitting only fish-eye and extreme telephoto. Some digicam lenses do start at the extreme wide-angle and zoom to medium telephoto. Most lenses intended for film cameras, such as those designed for the Nikon F-mount, the Pentax 'K' mount or the Canon EOS lens mount, can be used on certain D-SLR cameras, provided that the lens mounts are the same, both mechanically and electronically. Exceptions to this rule would be the new cameras from Nikon, notably the Nikon D-40 and D-40X, which require a 'G' type autonikkor lens. These two Nikon cameras lack the built-in autofocus motor to autofocus D-type autonikkors, so their lens interchangeability in regards to autofocusing is more limited than other digital Nikons. New lenses may use the same style of mount as film cameras, but have newer electronics for image stabilization and image control that a film camera would not recognize. Other lenses designed specifically for D-SLR's (e.g. Canon EF-S lenses or Nikon DX and some 'G' type Auto Nikkors) may not fit and work on the corresponding film or full-frame bodies; others will fit but their image circle may not cover the full film area and therefore yield an incomplete frame. The 'just-released' Nikon D3 uses what the manufacturer refers to as an FX format chip, which enables this camera to accept a wide range of Nikon mount lenses. The camera will also accept the older non-autofocus, AI-S-type lenses that were designed for cameras like the Nikon F3, the Nikon FA and the Nikon FM line, to name a few. Sensor size and quality The image sensor in a D-SLR is typically much larger than the one in a consumer-level digicam. A larger sensor allows better image quality, lower noise, shallower Depth Of Field , higher sensitivity, and increased latitude and Dynamic Range . Many D-SLR sensors are roughly APS-sized, that is, approximately 22 mm × 15 mm, a little smaller than the size of an APS-C film frame, much smaller than a frame of 135 Film . High-end digicams such as the Nikon Coolpix 8400 and the Coolpix 8800 have an 8.8 by 6.6 mm sensor (2/3 inch format, 11 mm diagonal), about five to seven times smaller area than a typical D-SLR sensor. Lower-end digicams have even smaller sensors, which usually, but not always, results in lower image quality than D-SLRs. Some digital SLRs have sensors the same size as 35mm film; such cameras are referred to as " Full-frame " cameras and are generally much more expensive. The Canon EOS 1Ds, the Canon 5D, and the Nikon D3 are examples of cameras using a full-frame sensor. Depth-of-field control The larger size of the sensors (and therefore lens focal lengths) of D-SLRs compared to digicams makes it much easier to limit the Depth Of Field , for example to emphasize a face by blurring the background. This reduced depth of field can be a disadvantage when the photographer prefers to take pictures where as much of the scene as possible is sharply rendered. Note that D-SLR's typically have lens apertures smaller than the typical digicam's aperture setting ability, which is usually f/8. This is a limitation of the small sensor. In contrast, a D-SLR can 'stop down' to f/16, f/22 or smaller aperture, depending upon the lens mounted on the camera and its f/stop range. Angle of view The Angle Of View of a lens depends upon its focal length and the camera's image sensor size; a sensor smaller than 35mm film format (36mm × 24mm frame) gives a narrower angle of view for a lens of a given focal length than does a camera equipped with a Full-frame (35mm) sensor. As of 2007 , only a few current D-SLRs have full-frame sensors, including the Canon EOS-1Ds Mark II and Canon EOS 5D ; the scarcity of full-frame D-SLRs is partly a result of the cost of such large sensors. Medium Format size sensors, such as those used in the Mamiya ZD among others, are even larger than full-frame (35mm) sensors, and capable of even greater image quality, but are even 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-equivalent focal length for a lens. Roughly APS-sized sensors have a crop factor of 1.5 to 1.7, so a lens with a focal length of 50mm will give a field of view equal to that of a 75mm to 85mm lens on a full-frame camera. This crop factor makes achieving long telephoto images on an APS-sensor camera 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 F-number and field of view. Mode dial Digital SLR cameras, along with most other digital cameras, generally have a Mode Dial to access standard camera settings or automatic scene-mode settings. Sometimes called a "PASM" dial, they typically provide as minimum Program, Aperture-priority, Shutter-priority, and full Manual modes. Scene modes vary and are inherently less customizable. They often include full-auto, landscape, portrait, action, macro, and night modes, among others. Professional D-SLRs seldom contain automatic scene modes. Live preview Depending on the position of the reflex mirror, the light from the scene can only reach either the Viewfinder or the sensor. Therefore, most D-SLRs don't currently provide " Live Preview " (allowing Focusing , Framing , and depth-of-field preview using the display), a facility that is always available on digicams. As of the summer of 2007, it is becoming more common for D-SLRs to provide live preview. The Canon EOS-1D Mark III , Canon EOS-1Ds Mark III , Canon EOS 40D , Nikon D3 , Nikon D300 , Olympus E-330 , Olympus E-410 , Olympus E-510 , Panasonic Lumix DMC-L1 , and Leica Digilux 3 all provide continuous live preview as an option. Additionally, the Fujifilm FinePix S5 Pro offers 30 seconds of live preview. Unusual features – infrared and ultraviolet photography On July 13, 2007, FujiFilm announced the FinePix IS Pro, which uses Nikon F-mount lenses. This camera, in addition to having live preview, has the ability to record in the infrared and ultraviolet spectrums of light. (See for a discussion of same) Medium format digital Many Medium Format roll-film SLRs can accept a Digital Camera Back to turn the camera into a D-SLR with very high image resolution and quality (typically 22–39 megapixels as of January 2007). However, the combination is very expensive and bulky, and more suited to still life than to action photography. As of 2007 integrated medium formats like the Hasselblad H System[http://www.hasselblad.com/products/h-system.aspx Hasselblad H System]. and Leaf AFi[http://www.leaf-photography.com/pages/products/leafafi.aspx Leaf AFi]. have started to appear. HISTORY At Photokina 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 body shared many features with the N8008. 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. A brief info on Kodak DCS-Series Digital Still SLR cameras , Photography in Malaysia Over the next decade, D-SLRs have been released by various companies such as Canon , Nikon , Kodak , Pentax , Olympus , Panasonic , Samsung , Konica Minolta , which was acquired by SONY, Fujifilm , and Sigma with higher resolution and lower prices. In 1999, Nikon announced the Nikon D1 , the first D-SLR to truly compete, 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 35mm film for these markets. In January 2000, Fujifilm announced the FinePix S1 Pro , the first D-SLR marketed to non-professionals. In 2003, Canon introduced the 6.3 Megapixel EOS 300D SLR camera (known in the United States as the Digital Rebel) with an MSRP of US$999. Its popularity encouraged other manufacturers to produce affordable digital SLR cameras, lowering entry costs and allowing more amateur photographers to purchase D-SLR's. Since 2003, the number of megapixels in imaging sensors have increased steadily, with most companies focusing on build quality, high ISO performance, speed, the elimination of digital 'noise' produced by the imaging sensor, and price reductions to lure new customers. PRESENT DAY Canon , Fujifilm , Nikon , Olympus , Panasonic , Pentax , Sigma , and Sony are currently producing D-SLR models. Canon's EOS digital line includes the 400D , 30D , 5D and the 1D Mark III . Canon's latest cameras, the 40D and the 1Ds Mark III were introduced on August 20, 2007. All current Canon D-SLRs use CMOS sensors. Nikon also has a broad line of D-SLRs which includes the D40 , D40x , D80 , D200 , D2Hs and D2Xs . Nikon announced two new cameras on August 23, 2007, the D300 and the D3 , the company's first full frame D-SLR. Fujifilm sells D-SLR cameras compatible only with Nikon lenses, the FinePix S5 Pro . Typically, their cameras tout high dynamic range and low "noise" as a competitive advantage. Olympus, together with Panasonic and Leica, make D-SLR cameras that conform to the Four Thirds System , including several models that feature a Live Preview LCD in addition to the viewfinder, and in-body Image Stabilization (Olympus only), or Image Stabilization lens (Leica/Panasonic). Pentax (partner with Samsung) and Sony (previously Konica Minolta ) also produce D-SLRs with in-body Image stabilization. Sigma produces an innovative D-SLR with the multi-layered Foveon X3 Sensor to deliver excellent color and detail. Hasselblad and Mamiya produce medium format-sized D-SLRs which produce the highest quality digital images. Their higher-resolution sensors (over 39 megapixels in some cases) are able to capture much more detail than the 35mm full-frame and smaller sensors found in other cameras. DIGITAL SLR VERSUS SLR-LIKE ("BRIDGE") AND COMPACT CAMERAS Non-SLR digital cameras are of two types: SLR-like Bridge Digital Camera s (also known as advanced digital cameras), and digicams. Both have permanently fixed lenses. SLR-like cameras – "bridge cameras" The "SLR-like" or "advanced" cameras (e.g. the Olympus SP series, some Nikon Coolpix models, the Sony Cyber-shot DSC V, DSC H, DSC F and DSC R series, the Panasonic FZ series, the Canon PowerShot A , G , S and Pro models, Minolta DiMAGE 7/7i/7hi , A1 , A2, A200, and several Fujifilm FinePix models) offer through-the-lens (TTL) viewing through the focusing lens, projected onto its eye-level electronic viewfinder (EVF) as well as the rear LCD screen. The difference compared to a D-SLR is that the viewfinder shows a digitally created copy of the TTL image, whereas the viewfinder in a D-SLR shows the actual optical TTL image via its mirror. An EVF image reacts more slowly 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 D-SLR with its reflex viewing system. The limitation of a bridge digital camera is its fixed lens, typically limited to about a 12:1 focal-length range. On the other hand, the fixed lens minimizes the risk of getting dust on the imaging sensor. Several of the high-end bridge cameras have a movable LCD screen (e.g. Canon PowerShot Pro1 and Konica Minolta A200 ), 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. High-end bridge cameras such as the Konica Minolta A200 provide Image Stabilization via CCD sensor shift; this stabilization can reduce the blurring effect of camera shake. Digicams (compact 'point-and shoot' digital cameras) Digicams, some commonly referred to as 'point-and-shoot' cameras because of their ease of use, can usually be operated at arm's length using only the LCD display screen at the rear of the camera. Some models also have simple optical viewfinders like traditional compact 35mm film cameras. Like the SLR-like bridge cameras, digicams lack the ability to accept interchangeable lenses, with the exception of certain digital rangefinder cameras such as the Leica M8 and the Epson RD-1, which use the Leica M-mount lens system. Most digicams are manufactured with a zoom lens that covers the most commonly used fields of view. Digicams may be altered through the use of supplementary add-on lens converters to provide an increase in the telephoto effect (greater magnification) or a wider angle field of view (greater lens angle of view), though the image quality is usually affected to a significant degree. Most digicams are significantly slower in image capture (time measured from pressing the shutter release to the writing of the digital image to the storage medium) than D-SLR cameras. This is a significant disadvantage for action, wildlife, sports and other photography requiring a fast frames-per-second image capture rate. Their zoom lenses can frequently have a much slower (smaller) effective wide-open aperture ( F-number ) than D-SLR or bridge cameras, especially at the telephoto end, which further limits their utility in situations involving low light levels and moving subjects. Image Stabilization is a feature available in some digicams that can effectively remedy the issue of camera-shake in low-light conditions without moving subjects and therefore reduce blurring in low-light photographs. SEE ALSO REFERENCES EXTERNAL LINKS
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