Most digital single-lens reflex cameras (digital SLR or DSLR) are digital cameras that use 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 three times by the roof 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 not to delay an action photo.

All of this happens automatically over a period of milliseconds, with cameras designed to do this 3–10 times per 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, as well as their comparatively high signal to noise ratio.

The term DSLR generally refers to cameras that resemble 35 mm format cameras, although some medium format cameras are technically DSLRs.

Comparison with digital point-and-shoot camera

The reflex design scheme is a major difference between a DSLR and an ordinary digital point-and-shoot camera, which typically exposes the sensor constantly to the light projected by the lens, allowing the camera's screen to be used as an electronic viewfinder.

DSLR design principles

1. 4-element lens
2. Reflex mirror
3. Focal-plane shutter
5. Matte focusing screen
6. Condenser lens
7. Pentaprism
8. Eyepiece

A camera based on the single-lens reflex (SLR) principle uses a mirror to show in a viewfinder the image that will be captured. The cross-section (side-view) of the optical components of an SLR shows how the light passes through the lens assembly (1), is reflected into the pentaprism by the reflex mirror (which must be at an exact 45-degree angle) (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 is projected through the eyepiece (8) to the photographer's eye. Focusing is either automatic, activated by pressing half-way on the shutter release or a dedicated AF button, as is mainly the case with an autofocusing film SLR; or manual, where the photographer manually focuses the lens by turning a lens ring on the lens barrel. When an image is photographed, the mirror swings upwards in the direction of the arrow, the focal-plane shutter (3) opens, and the image is projected and captured on the sensor (4), after which actions, the shutter closes, the mirror returns to the 45-degree angle, the diaphragm reopens, and the built in drive mechanism re-tensions the shutter for the next exposure. There is often a ring of soft material around the focusing screen, which helps to both cushion the impact of the mirror slapping up and helps seal the mirror box from light entering through the eye piece. Some high-end cameras incorporate a shutter into the eyepiece to further eliminate light that may enter there during long exposures.

Phase-detection autofocus

The diagram shown here is an over-simplification in that it omits the sensors used to activate the drive for the autofocus system. Those sensors reside at the bottom of the mirror box. In such a system, the main mirror is slightly translucent in the center, which allows light to pass through it to a secondary mirror which reflects light to the sensors below.

DSLRs typically use a phase detection autofocus system. This method of focus is very fast, and results in less focus "searching", but requires the incorporation 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 must use contrast-detect autofocus instead, which is slower in some implementations.

DSLR optical viewfinder vs. digital point-and-shoot camera LCD

Depending on the viewing position of the reflex mirror (down or up), the light from the scene can only reach either the viewfinder or the sensor. Therefore, many older DSLRs do not provide "live preview" (allowing focusing, framing, and depth-of-field preview using the display), a facility that is always available on digicams although today most DSLRs offer live view.

The advantages of an optical viewfinder are that it alleviates eye-strain sometimes caused by electronic view finders (EVF), and that it constantly shows (except during the time for the sensor to be exposed) the exact image that will be exposed because its light is routed directly from the lens itself. Compared to ordinary digital cameras with their LCDs and/or electronic viewfinders the advantage is that there is no time lag in the image; it is always correct as it is being "updated" at the speed of light. This is important for action and/or sports photography, or any other situation where the subject or the camera is moving too quickly. Furthermore, the "resolution" of the viewed image is much better than that provided by an LCD or an electronic viewfinder, which can be important if manual focusing is desired for precise focusing, as would be the case in macro photography and "micro-photography" (with a microscope).

Compared to some low cost cameras that provide an optical viewfinder that uses a small auxiliary lens, the DSLR design has the advantage of being parallax-free; that is, it never provides an off-axis view.

A disadvantage of the DSLR optical viewfinder system is that while it is used it prevents the possibility of using the LCD for viewing and composing the picture before taking it. Some people prefer to compose pictures on the display – for them this has become the de-facto way to use a camera. Electronic viewfinders may also provide a brighter display in low light situations, as the picture can be electronically amplified; conversely, LCDs can be difficult to see in very bright sunlight.

DSLRs with live preview

Early DSLRs lacked the ability to show the optical viewfinder's image on the LCD display, a feature known as live preview. Live preview is useful in situations where the camera's eye-level viewfinder cannot be used, such as underwater photography where the camera is enclosed in a plastic waterproof case.

Olympus introduced the Olympus E-10 in the summer of 2000, which was the first DSLR with live preview – albeit an atypical design with a fixed lens. , some DSLRs from Canon, Nikon, Olympus, Panasonic, Leica, Pentax, Samsung and Sony all provide continuous live preview as an option. Additionally, the Fujifilm FinePix S5 Pro offers 30 seconds of live preview.

On all DSLRs that offer live preview via the primary sensor, the phase detection autofocus system does not work in the live preview mode, and the DSLR switches to a slower contrast system commonly found in point & shoot cameras. While even phase detection autofocus requires contrast in the scene, strict contrast detection autofocus is limited in its ability to find focus quickly, though it is somewhat more accurate.

Some live preview systems make use of the primary sensor to provide the image on the LCD (which is the way all non-DSLR digicams work), and some systems use a secondary sensor. Possible advantages of using a secondary sensor for live preview is to avoid additional noise that might result from the primary sensor heating up from continuous use and allowing faster auto-focus via phase autofocus.

A new feature via a separate software package introduced from Breeze Systems in October 2007, features live view from a distance. The software package is named "DSLR Remote Pro v1.5" and enables support for the Canon EOS 40D and 1D Mark III.

High definition DSLRs

Introduced in 2008, HDSLRs are DSLRs which offer a movie mode capable of recording high definition motion video. The first DSLR introduced with an HD movie mode, the Nikon D90, captures video at 720p24 (1280x720 resolution at 24 frame/s). Other early HDSLRs capture video using a nonstandard video resolution or frame rate. For example, the Pentax K-7 uses a nonstandard resolution of 1536×1024, which matches the imager's 3:2 aspect ratio. The Canon EOS 500D (Rebel T1i) uses a nonstandard frame rate of 20 frame/s at 1080p, along with a more conventional 720p30 format.

In general, HDSLRs use the full imager area to capture HD video, though not all pixels (causing video artifacts to some degree.) Compared to the much smaller image sensors found in the typical camcorder, the HDSLR's much larger sensor yields distinctly different image characteristics. HDSLRs can achieve much shallower depth of field and superior low-light performance. However, the low ratio of active pixels (to total pixels) is more susceptible to aliasing artifacts (such as moire patterns) in scenes with particular textures, and CMOS rolling shutter tends to be more severe. Furthermore, due to the DSLR's optical construction, HDSLRs typically lack one or more video functions found on standard dedicated camcorders, such as autofocus while shooting, powered zoom, and an electronic viewfinder/preview. These and other handling limitations prevent the HDSLR from being operated as a simple point-and-shoot camcorder, instead demanding some level of planning and skill for location shooting.

Video functionality has continued to improve since the introduction of the HDSLR. HD movie mode is now offered on many DSLRs, from entry level (such as the Canon EOS 550D (Rebel T2i) and Nikon D5000) to professional level (such as the Canon EOS 5D Mark II and Canon 1D Mark IV.) Among the improvements include higher video resolution (such as 1080p24) and video bitrate, improved automatic control (autofocus) and manual exposure control, and support for formats compatible with high-definition television broadcast, Blu-ray disc mastering or Digital Cinema Initiatives (DCI).

The rapid maturation of HDSLR cameras has sparked a revolution in digital filmmaking. The Canon EOS 5D Mark II (with the release of firmware version 2.0.3/2.0.4.) and Panasonic Lumix GH1 were the first HDSLRs to offer broadcast compliant 1080p24 video, but since then, the list of models with comparable functionality has grown considerably. An increased number of films, documentaries, television shows, and other productions are utilizing the quickly improving features. One such project is the "Story Beyond the Still" contest from Canon. This contest asked filmmakers to collectively shoot a short film in 8 chapters. Each chapter was shot in only a couple of weeks and a winner was determined for each chapter. Then the winners collaborated to shoot the final chapter of the story. "Shot On DSLR" is a quickly growing phrase among independent filmmakers. The movement has even inspired a branding: the "Shot On DSLR Badge". This badge is simply to raise awareness of the new capabilities and incredible imagery produced by today's DSLR cameras.

Concerning using a DSLR camera as a video camera, some manufacturers make optional accessories to assist filmmakers feel as using real video/film camera. One of them is External EVF with 1.2 million pixels.

DSLR 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.

Lens mounts and lens manufacturers

Interchangeable lenses for SLRs and DSLRs (also know as "Glass") are built to operate correctly with a specific lens mount that is generally unique to each brand. A photographer will often use lenses made by the same manufacturer as the camera body (for example, Canon EF lenses on a Canon body) although there are also many independent lens manufacturers, such as Sigma, Tamron, Tokina, and Vivitar, to name a few, that make lenses for a variety of different lens mounts. There are also lens adapters that allow a lens for one lens mount to be used on a camera body with a different lens mount but with often reduced functionality.

Many lenses are mountable, "diaphragm-and-meter-compatible", on modern DSLRs and on older film SLRs that use the same lens mount. Most DSLR manufacturers have introduced lines of lenses with image circles and focal lengths optimized for the smaller sensors generally offered for existing 35 mm mount DSLRs, mostly in the wide angle range. These lenses tend not to be completely compatible with full frame sensors or 35 mm film because of the smaller imaging circle and, with some Canon EF-S lenses, interference with the reflex mirrors on full-frame bodies. Several manufacturers produce full-frame digital SLR cameras that allow lenses designed for the 35 mm film frame to operate at their intended angle of view.

DSLR design considerations

Pentaprism vs. penta-mirror

Most of the entry level DSLRs use a pentamirror instead of the traditional pentaprism. The pentamirror design is composed mostly of plastic and is lighter and cheaper to produce — however, the image in the viewfinder is usually darker.

Sensor size and image quality

Image sensors used in DSLRs come in a range of sizes. The very largest are the ones used in "medium format" cameras, typically via a "digital back" which can be used as an alternative to a film back. Because of the manufacturing costs of these large sensors the price of these cameras is typically over $20,000 .

With the exception of medium format DSLRs, the largest sensors are referred to as "full-frame" and are the same size as 35 mm film (135 film, image format 24×36 mm); these sensors are used in high-end DSLRs such as the Canon EOS-1Ds Mark III, the Canon EOS 5D Mark II, the Nikon D700, the Nikon D3, the Nikon D3X, the Sony Alpha 850 and the Sony Alpha 900. Most modern DSLRs use a smaller sensor commonly referred to as APS-C sized, that is, approximately 22 mm × 15 mm, a little smaller than the size of an APS-C film frame, or about 40% of the area of a full-frame sensor. Other sensor sizes found in DSLRs include the Four Thirds System sensor at 26% of full frame, APS-H sensors (used, for example, in the Canon EOS-1D Mark III) at around 61% of full frame, and the Foveon X3 sensor at 33% of full frame.

The sensors used in current DSLRs are much larger than the sensors found in digicam-style cameras, most of which use sensors known as 1/2.5", whose area is only 3% of a full frame sensor. Even high-end digicams such as the Canon PowerShot G9/G10/G11 or the Nikon CoolPix P5000/P6000 use sensors that are approximately 5% and 4% of the area of a full frame sensor, respectively. The current exceptions are the Micro Four Thirds system by Olympus and Panasonic, the Sigma DP1, which uses a Foveon X3 sensor, and the Leica X1. Leica offers an "S-System" DSLR with a 30×45mm array containing 37 million pixels. This sensor is 56% larger than a full-frame sensor.

There is a connection between sensor size and image quality; in general, a larger sensor provides lower noise, higher sensitivity, and increased latitude and dynamic range. There is also a connection between sensor size and depth of field, with the larger sensor resulting in shallower depth of field at a given aperture.

Table of sensor sizes

The table lists dimensions of typical DSLR sensors.

{| style="width:95%; text-align:center;" class="wikitable" ! Type !! Four Thirds !! Sigma FoveonX3 !! Canon APS-C !! Sony · Pentax · Sigma · Samsung APS-C / Nikon DX !! Canon APS-H !! 35mm Full-frame/ Nikon FX !! Leica S2!! Pextax 645D!! Phase One P 65+ |- ! Diagonal (mm) | 21.6 || 24.9 || 26.7 || 28.2-28.4 || 33.5 || 43.2-43.3 || 54|| 55|| 67.4 |- ! Width (mm) | 17.3 || 20.7 || 22.2 || 23.6-23.7 || 27.9 || 36 ||45|| 44|| 53.9 |- ! Height (mm) | 13.0 || 13.8 || 14.8 || 15.6 || 18.6 || 23.9-24 || 30||33|| 40.4 |- ! Area (mm²) | 225 || 286 || 329 || 368-370 || 519 || 860-864 || 1350||1452|| 2178 |- ! Crop factor | 2.00 || 1.74 || 1.62 || 1.52-1.54 || 1.29 || 1.0 || 0.8||0.78|| 0.64 |}

Depth-of-field control

The lenses typically used on DSLRs have a wider range of apertures available to them, ranging from as large as 1.0 to about 32. Lenses for digicams rarely have true available aperture sizes much larger than 2.8 or much smaller than 5.6.

The 5.6 limitation is because lens designs of typical small sensor digicams already produce diffraction blur bigger than a few pixels at 5.6. Because of digicams' smaller sensors there are a limited number of apertures available that will produce an acceptably sharp image. Many digicams only have a two-stop range of apertures because at settings outside of these the image will become too soft because of limits of lens design at large apertures, or diffraction at smaller apertures. To help extend the exposure range, some digicams will also incorporate an ND filter pack into the aperture mechanism.

The apertures that digicams have available give much more depth of field than equivalent angles of view on a DSLR. For example a 6 mm lens on a 2/3" sensor digicam has a field of view similar to a 24 mm lens on a 35 mm camera. At an aperture of 2.8 the digicam (assuming a crop factor of 4) has a similar depth of field to that 35 mm camera set to 11 – that's a four-stop difference. Put another way, with both cameras at 2.8 and focused on a subject 1 meter from the camera, and both cameras zoomed to produce the same angle of view (35 mm camera will need to use larger focal length to produce same angle of view from same distance), the digicam might have a depth of field of 2 meters and the larger camera would have a depth of field of 0.3 meters.

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 35 mm film format (36 mm × 24 mm frame) gives a narrower angle of view for a lens of a given focal length than a camera equipped with a full-frame (35 mm) sensor. As of 2008, only a few current DSLRs have full-frame sensors, including the Sony α 900, Canon EOS-1Ds Mark III, Canon 5D, Nikon D3x and Nikon D700. The scarcity of full-frame DSLRs 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 (35 mm) sensors, and capable of even greater resolution, and are correspondingly 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. Typical APS-C sensors have crop factors of 1.5 to 1.7, so a lens with a focal length of 50 mm will give a field of view equal to that of a 75 mm to 85 mm lens on a 35 mm camera. The smaller sensors of Four Thirds System cameras have a crop factor of 2.0.

While the crop factor of APS-C cameras effectively ''narrows'' the angle of view of long-focus (telephoto) lenses, making it easier to take close-up images of distant objects, ''wide''-angle lenses suffer a reduction in their angle of view by the same factor.

DSLRs with "crop" sensor size have slightly more depth-of-field than cameras with 35 mm sized sensors for a given angle of view. The amount of added depth of field for a given focal length can be roughly calculated by multiplying the depth of field by the crop factor. Shallower depth of field is often preferred by professionals for portrait work and to isolate a subject from its background.

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 DSLRs seldom contain automatic scene modes because professionals understand their equipment and can quickly adjust the settings to take the image that they want.

Dust reduction systems

The fact that it is possible to change lenses on a DSLR results in the possibility of dust entering the camera body and adhering to the image sensor. This can reduce image quality, and make it necessary to clean the sensor. Various techniques exist including using a cotton swab with various fluids or blowing with compressed air. Some people prefer to clean the sensor themselves and some send the camera in for service.

A method to prevent dust entering the chamber, by using a "dust cover" filter right behind the lens mount, was pioneered by Sigma in their first DSLR, the Sigma SD9, in 2002.

Olympus pioneered a built-in sensor cleaning facility in their first DSLR that had a sensor exposed to air, the Olympus E-1, in 2003. Other DSLR manufacturers followed suit, and dust reduction systems are becoming common in DSLRs. There is some controversy as to how effective these systems are; see dust reduction system for more information.

Medium format digital

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 21–60 megapixels as of July 2009). However, the combination is very expensive and bulky, and more suited to still life than to action photography. Another potential disadvantage of medium format digital backs is that there are none currently available (as of early 2008) that incorporate a low-pass filter (aka optical anti-aliasing filter) except for the Mamiya ZD, which has a removable one. This is done to allow the maximum resolution to be extracted from a given image, but at the cost of moiré.

integrated medium formats like the Phase One 645 system, Hasselblad H System and Leaf AFi have started to appear.

Unusual features

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 spectra of light.

In August 2010 Sony released series of DSLRs allowing 3D photography. It was accomplished by sweeping the camera horizontally or vertically in Sweep Panorama 3D mode. The picture could be saved as ultra-wide panoramic image or as 16:9 3D photography to be viewed on BRAVIA 3D television set.

History

In 1969 Willard S. Boyle and George E. Smith invented the first successful imaging technology using a digital sensor, a CCD (Charge-Coupled Device). CCD would allow the rapid development of digital photography. For his contribution to digital photography Boyle and Smith were granted the Nobel Prize in Physics 2009.

In 1975 Kodak engineer Steven Sasson invented the first digital still camera, which used a Fairchild 100 x 100 pixel CCD.

On August 25, 1981 Sony unveiled a prototype of 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. The prototype body shared many features with the N8008. The follower Nikon QV-1000C Still Video Camera was produced since 1988 mainly for professional press use. Both cameras used QV mount lenses, a variant of F-mount lenses. Via an adapter (QM-100) other Nikon F-mount lenses can be fitted.

In 1991, Kodak released the first commercially available fully digital SLR, the Kodak DCS-100, previously shown at Photokina in 1990. 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 and other Kodak DCS cameras.

In 1999, Nikon announced the Nikon D1. The D1 shared similar body construction as Nikon's professional 35mm film DSLRs, and the same Nikkor lens mount, allowing the D1 to use Nikon's existing line of AI/AIS manual-focus and AF lenses.

Over the next decade, other camera manufacturers entered the DSLR market, including Canon, Kodak, Fujifilm, Minolta (later Konica Minolta, and ultimately acquired by Sony), Pentax, Olympus, Panasonic, Samsung, Sigma, and Sony).

In January 2000, Fujifilm announced the FinePix S1 Pro, the first consumer-level DSLR.

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, aimed at the consumer market. Its commercial success encouraged other manufacturers to produce competing digital SLRs, lowering entry costs and allowing more amateur photographers to purchase DSLRs.

In 2004 Konica Minolta released Konica Minolta Maxxum 7D, first DSLR with in-body image stabilization which later on become standard in Pentax, Olympus and Sony Alpha cameras.

In early 2009 Nikon released D90, first DSLR to feature video recording. Since then all major companies offer cameras with this functionality.

In September 2009 Sony released the first sub-2000 USD full frame DSLR, the Sony Alpha 850, creating accessible full frame camera for amateur photographers.

Since then the number of megapixels in imaging sensors have increased steadily, with most companies focusing on, 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.

Market share

, DSLR sales are dominated by Canon's and Nikon's offerings. For 2007, Canon edged out Nikon with 41% of worldwide sales to the latter's 40%, followed by Sony and Olympus each with approximately 6% market share. In the Japanese domestic market, Nikon captured 43.3% to Canon's 39.9%, with Pentax a distant third at 6.3%.

The duopoly of Canon and Nikon is sometimes referred to as "Canikon" or "Nikanon" in online forums in skeptical challenge to the presumptive acceptance of these manufacturer's cameras as always "the best". Nevertheless, Canon and Nikon have used their professional market presence especially persuasively in the sale of entry level offerings. Online contributors often challenge the "Canikon/Nikanon" supposed superiority when they believe there are superior innovations from the smaller DSLR manufacturers.

The DSLR market is dominated by Japanese companies, including all of the top five manufacturers (Canon, Nikon, Olympus, Pentax, and Sony), as well as Fujifilm, Mamiya, Panasonic, and Sigma. Leica is German, Hasselblad is Swedish, and Samsung is Korean, while the American company Kodak formerly produced DSLRs as well.

Present-day models

Mainstream DSLRs (full-frame or smaller image sensor format) are currently produced by Canon, Leica, Nikon, Olympus, Pentax, Samsung, Sigma, and Sony. Phase One, Leaf, Linhof, Hasselblad and Mamiya, amongst others, produce expensive, high-end medium-format view-cameras.

Canon's current 2011 EOS digital line includes the Canon EOS 1100D, 550D, 600D, 60D, 7D, 5D Mark II, 1Ds Mark III, and the 1D Mark IV. , all current Canon DSLRs use CMOS sensors.

Fujifilm has discontinued all D-SLR models, including the Fujifilm FinePix S5 Pro DSLR, compatible with the Nikon F-mount lens system. It is based on the Nikon D200 camera body, but utilizes Fuji's sensor technology (Fujifilm SuperCCD SR Pro) and menu system. Fuji previously offered the Fujifilm FinePix IS Pro, which has the unique ability to capture light in the infrared and ultraviolet spectrums.

Nikon also has a broad line of DSLRs currently including the D3100, D5100, D90, D7000, D300S, D700, D3S and the D3X. The D3, announced in August 2007, is the company's first full-frame digital SLR. Olympus makes DSLR cameras and lenses as part of the Four Thirds System. Current Olympus models include the E-620, E-30 and E-5. Unique features include a smaller size, an effective sensor dust reduction system, and in-body image stabilization, along with a crop factor of 2 (compared to 1.6 in most DSLR's) and an aspect ratio of 4:3 (instead of 3:2). Four Thirds lenses are especially highly regarded. Pentax currently offers the Pentax K-5, Pentax K-r, Pentax K-x, Pentax K-7 (though the later two are discontinued, and the medium format Pentax 645D, while Samsung (in collaboration with Pentax) offers the Samsung GX-20, a clone of the K20D. Innovative features include in-body image stabilization, dust reduction system, use of standard AA batteries in the K-x and K-r, weather-proof sealing in the K-5/K-7 (first introduced on the K10D, and otherwise found only in more expensive semi-pro models like the Nikon D200), and adoption of Adobe's DNG standard raw image format. Also, they offer extensive backwards compatibility, accepting all Pentax K mount lenses made since 1975 (though the automatic light metering functionality of some early lenses does not work).

Sigma produces DSLRs using the Foveon X3 sensor, rather than the conventional Bayer sensor. This is claimed to give higher colour resolution although headline pixel counts are lower than conventional Bayer-sensor cameras. Their current model is the Sigma SD14. Sigma is the only DSLR manufacturer which sells lenses for other brands' lens mounts.

Currently Sony offer is focused mostly on Entry-level and Midrange cameras, with addition of two professional full-frame DSLRs: α900 and α850. Entry level offer is made of two cameras: Sony Alpha 290 without Live View and Sony Alpha 390 with it, and tiltable LCD. Midrange cameras are Sony Alpha 450, cheap, classic DSLR without Quick AF Live View, though bigger viewfinder, Sony Alpha 560 and Sony Alpha 580 featuring video recording, 3D photography and set of more advanced functions, and finally Sony Alpha 33 and Sony Alpha 55 featuring full time phase detection autofocus during video recording as well as continuous shooting of up to 10 frame/s. The α series offers in-body sensor-shift image stabilization and retains the Minolta AF lens mount.

Hasselblad, Linhof, Leaf, Mamiya and Phase One, amongst others, produce medium format-sized (6x4.5 cm., 6x6cm.) view-cameras, which produce high resolution digital images. Their sensors (over 60 megapixel in some cases) are able to capture much more detail than the full-frame and smaller sensors found in DSLR cameras.

DSLRs compared to other digital cameras

Fixed-lens cameras

Non-SLR digital cameras generally fall into two types: compact digicams, and SLR-like bridge digital cameras (also known as advanced digital cameras) which offer larger zoom ranges, better optics, and more manual controls. Both types have permanently fixed lenses. While the only ''defining'' feature of an SLR is its reflex viewfinder system, extant digital SLR models generally offer the following advantages over fixed-lens cameras of the same generation:

Choice of interchangeable (and often higher-quality) lenses. Image sensors of much larger size and often higher quality, offering lower noise, which is useful in low light, and greater dynamic range.

Optical viewfinders which tend to be more comfortable and efficient, especially for action photography and in low-light conditions.

DSLRs often offer faster and more responsive performance, with less shutter lag, faster autofocus systems, and faster frame rates. The larger focal length for the same field of view allows creative use of depth of field effects. Ability to attach additional accessories including hot shoe-mounted flash units, battery grips for additional power and hand positions, external light meters, and remote controls

There are also certain drawbacks to current DSLR designs, when compared to common fixed-lens digital cameras:

Generally greater cost, size, and weight. Louder operation, due to the SLR mirror mechanism.

Potential contamination of the sensor by dust particles, when the lens is changed (though recent dust reduction systems alleviate this).

Small digicams generally can focus better on closer objects than typical DSLR lenses.

SLR-like cameras – "bridge cameras"

The "SLR-like" or "advanced" digicams offer a non-optical electronic through-the-lens (TTL) view through the focusing lens, via the eye-level electronic viewfinder (EVF) as well as the rear LCD. The difference in views compared to a DSLR is that the EVF shows a digitally created TTL image, whereas the viewfinder in a DSLR shows an actual optical TTL image via the reflex viewing system. An EVF image has lag time (that is, it reacts with a delay 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.

Bridge digital cameras with their fixed lenses are not usually subject to dust from outside the camera settling on the sensor. However having fixed lenses they are limited to the focal lengths they are manufactured with, except for what is available from attachments. Manufacturers have attempted (with increasing success) to overcome this disadvantage by offering extreme ranges of focal length on models known as superzooms, some of which offer far longer focal lengths than readily available DSLR lenses.

Current designs are limited by increasingly high pixel pitches, which limit their dynamic range and also call for increasingly higher quality lens designs. Exceptions to this trend are the Sigma DP1 with its 20.7×13.8 mm sensor and the Sony DSC-R1 with a 21.5×14.4  mm sensor.

Digicams (compact "point-and-shoot" digital cameras)

Digicams, 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 at the rear of the camera. Some models also have simple optical viewfinders like traditional compact 35 mm film cameras. Like the SLR-like bridge cameras, most 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, with "super-zoom" models becoming more popular. Digicam lenses can be adapted to telephoto or wide-angle as the above-mentioned "bridge-cameras."

Digicams were once significantly slower in image capture (time measured from pressing the shutter release to the writing of the digital image to the storage medium) than DSLR cameras, but this situation is changing with the introduction of faster capture memory cards and faster in-camera processing chips. Currently, however, these cameras present a significant disadvantage for action, wildlife, sports and other photography requiring a high burst rate (frames per second).

SLR-like interchangeable lens digital cameras

In late 2008, the Micro Four Thirds system became the latest camera system to compete with DSLRs. While the sensor size as the original Four Thirds System, the design removes the mirror and pentaprism in order to reduce the distance between the lens and sensor. Most, but not all, Micro Four Thirds cameras substitute the optical viewfinder of DSLRs with an electronic one. All mirrorless cameras feature a rear LCD screen, which serves as both a live-preview and playback monitor. Panasonic released the first Micro Four Thirds camera, the Lumix DMC-G1, and later released the Lumix DMC-GH1, which added a Full-HD movie-mode (1080, 24p). Several manufacturers have announced lenses for the new Micro Four Thirds mount, while older Four Thirds lenses can be mounted with an adapter (a mechanical spacer with front and rear electrical connectors and its own internal firmware).

A similar mirror-less interchangeable lens camera, but with an APS-C-sized sensor, was announced in January 2010: the Samsung NX10.

A handful of rangefinder cameras support interchangeable lenses. Three digital rangefinders exist, they are the Epson R-D1 (APS-C-sized sensor), the Leica M8 (APS-H-sized sensor), both smaller than 35 mm film rangefinder cameras, and the Leica M9, which is a full-frame camera.

See also

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Mirrorless interchangeable-lens camera (also known as "EVIL" camera)

Box camera

Canon

Comparison of digital single-lens reflex cameras

Digital photography

Four Thirds System

Fujifilm

Full-frame digital SLR

Kodak

Nikon

Olympus

|

Panasonic - Lumix

Sony

Optics

Photographic film

Pentax

Rangefinder camera

Scheimpflug principle

Single-lens reflex camera

Single-lens translucent camera

Twin-lens reflex camera

Zeiss Ikon

|}

References

Category:Cameras by type Category:Digital photography Category:Digital SLR cameras

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