Digital single-lens reflex camera
A digital single-lens reflex camera (also called a digital SLR or DSLR) is a digital camera combining the optics and the mechanisms of a single-lens reflex camera with a digital imaging sensor, as opposed to photographic film. The reflex design scheme is the primary difference between a DSLR and other digital cameras. In the reflex design, light travels through the lens, then to a mirror that alternates to send the image to either the viewfinder or the image sensor. The alternative would be to have a viewfinder with its own lens, hence the term "single lens" for this design. By using only one lens, the viewfinder presents an image that will not perceptibly differ from what is captured by the camera's sensor.
- 1 The design of DSLR cameras
- 2 Features commonly seen in DSLR designs
- 3 History
- 4 See also
- 5 References
- 6 External links
The design of DSLR cameras
Like SLRs DSLRs typically use interchangeable lenses (1) with a proprietary lens mount. A movable mechanical mirror system (2) is switched down (exact 45-degree angle) to direct light from the lens over a matte focusing screen (5) via a condenser lens (6) and a pentaprism/pentamirror (7) to an optical viewfinder eyepiece (8). Most of the entry level DSLRs use a pentamirror instead of the traditional pentaprism.
Focusing can be manual or automatic, activated by pressing half-way on the shutter release or a dedicated AF button. To take an image, 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 image sensor (4), after which actions, the shutter closes, the mirror returns to the 45-degree angle, and the built in drive mechanism re-tensions the shutter for the next exposure.
Compared to the newer concept of mirrorless interchangeable-lens cameras this mirror/prism system is the characteristic difference providing direct, accurate optical preview with separate autofocus and exposure metering sensors. Essential parts of all digital cameras are some electronics like amplifier, analog to digital converter, image processor and other (micro-)processors for processing the digital image, performing data storage and/or driving an electronic display.
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.
Features commonly seen in DSLR designs
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 ability to exchange lenses, to select the best lens for the current photographic need, and to allow the attachment of specialized lenses, is one of the key factors in the popularity of DSLR cameras, although this feature is not unique to the DSLR design and mirrorless interchangeable lens cameras are becoming increasingly popular. Interchangeable lenses for SLRs and DSLRs (also known 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 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. However, when lenses designed for 35 mm film or equivalently sized digital image sensors are used on DSLRs with smaller sized sensors, the image is effectively cropped and the lens appears to have a longer focal length than its stated focal length. Most DSLR manufacturers have introduced lines of lenses with image circles optimized for the smaller sensors and focal lengths equivalent to those 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, interfere with the reflex mirrors on full-frame bodies.
HD video capture
Since 2008, manufacturers have offered DSLRs capable of recording high-definition video.
In capturing HD video, HDSLRs use in general the full imager area, though not all pixels, causing video artifacts to some extent. 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 proportion of active pixels is more susceptible to aliasing artifacts (such as moiré patterns) and the CMOS rolling shutter tends to be more noticeable. Furthermore, due to the DSLR's optical construction, HDSLRs typically lack one or more video functions found on other camcorders, such as autofocus while shooting; powered zoom; and an electronic viewfinder. 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 shooting.
Video functionality has continued to improve since the introduction of the HDSLR. Among the improvements include higher-resolution video (such as 1080p24); improved autofocus and manual exposure control; support for formats compatible with high-definition television broadcast; Blu-ray disc mastering;
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 northern-hemisphere summer of 2000, which was the first DSLR with live preview – albeit an atypical design with a fixed lens. In late 2008[update], some DSLRs from Canon, Nikon, Olympus, Panasonic, Leica, Pentax, Samsung and Sony all provided 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.
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.
Larger sensor sizes and better 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 as of December 2007[update]
"Full-frame" is the same size as 35 mm film (135 film, image format 24×36 mm); these sensors are used in DSLRs such as the Canon EOS-1D X and 5D Mark III, and the Nikon D800, D4, D610, and Df. Most modern DSLRs use a smaller sensor that is APS-C sized, which is approximately 22×15 mm, slightly 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 original Foveon X3 sensor at 33% of full frame (although as of 2013, current Foveon sensors are APS-C sized).
The sensors used in current DSLRs are much larger than the sensors found in common digital cameras, most of which use sensors known as 1/2.5″, which is 3% the size of a full frame sensor. Some compacts, however, however, use larger sensors. Examples include the Sigma DP1, which uses a Foveon X3 sensor; the Leica X1; the Canon PowerShot G1 X, which uses a 1.5″ (18.7×14 mm) sensor that is slightly larger than the Four Thirds standard and is 30% of a full-frame sensor; the Nikon Coolpix A, which uses an APS-C sensor of the same size as those found in the company's DX-format DSLRs; and two models from Sony, the RX100 with a 1″-type (13.2×8.8 mm) sensor with about half the area of Four Thirds and the full-frame Sony RX1.
|Type||Four Thirds||Sigma Foveon
|Canon APS-C||Sony · Pentax · Sigma · Samsung
APS-C / Nikon DX
|Canon APS-H||35 mm Full-frame
/ Nikon FX
|Leica S2||Pentax 645D||Phase One P 65+|
The lenses typically used on DSLRs have a wider range of apertures available to them, ranging from as large as f/1.0 to about f/32. Lenses for smaller sensor cameras rarely have true available aperture sizes much larger than f/2.8 or much smaller than f/5.6.
To help extend the exposure range, some smaller sensor cameras will also incorporate an ND filter pack into the aperture mechanism.
The apertures that smaller sensor cameras 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 f/2.8 the smaller sensor camera (assuming a crop factor of 4) has a similar depth of field to that 35 mm camera set to f/11.
Wider 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 (36×24 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 2013, only a few current DSLRs have full-frame sensors, including the Canon EOS-1D X, EOS 5D Mark III, and EOS 6D; and the Nikon D3X, Nikon D4, Nikon D610, Nikon D800, and Nikon Df. 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.
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.
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 their contribution to digital photography Boyle and Smith were awarded the Nobel Prize for Physics in 2009.
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.
In the Spring of 1987, the Kodak Research Labs integrated their 1.3 MP image sensor with a film DSLR camera. The Imaging Systems Lab at KRL designed circuitry to sync imager exposure with the mechanical shutter of the widely used Nikon F3 SLR through its motor drive contacts. Digital images were stored on a tethered hard drive and processed for histogram feedback to the user. The system was refined with input from the Associated Press and demonstrated at Photokina 1988. This became the first commercial DSLR, launched by Kodak in 1991.
In 1999, Nikon announced the Nikon D1. The D1's body was similar to Nikon's professional 35 mm film SLRs, and it had the same Nikkor lens mount, allowing the D1 to use Nikon's existing line of AI/AIS manual-focus and AF lenses. Although Nikon and other manufacturers had produced digital SLR cameras for several years prior, the D1 was the first professional digital SLR that displaced Kodak's then-undisputed reign over the professional market.
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 (whose camera division is now owned by Ricoh), 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 and Canada 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.
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.
In June 2012, Canon announced the first DSLR to feature a touchscreen, the EOS 650D/Rebel T4i/Kiss X6i. Although this feature had been widely used on both compact cameras and mirrorless models, it had not made an appearance in a DSLR until the 650D.
The DSLR market is dominated by Japanese companies and the top five manufacturers are Japanese: Canon, Nikon, Olympus, Pentax, and Sony. Other manufacturers of DSLRs include Mamiya, Sigma, Leica (German), and Hasselblad (Swedish).
In 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%.
For Canon and Nikon, digital SLRs are their biggest source of profits. For Canon, their DSLRs brought in four times the profits from compact digital cameras, while Nikon earned more from DSLRs and lenses than with any other product. Olympus and Panasonic have since exited the DSLR market and now focus on producing mirrorless cameras.
Currently DSLRs are widely used by consumers and professional still photographers. Well established DSLRs currently offer a larger variety of dedicated lenses and other photography equipment. Mainstream DSLRs (in full-frame or smaller image sensor format) are produced by Canon, Nikon, Pentax, and Sigma. Pentax, Phase One, Hasselblad, and Mamiya Leaf produce expensive, high-end medium-format DSLRs, including some with removable sensor backs. Contax, Fujifilm, Kodak, Panasonic, Olympus, Samsung, and Sony previously produced DSLRs, but now either offer non-DSLR systems or have left the camera market entirely. Konica Minolta's line of DSLRs was purchased by Sony.
- Canon's current 2013 EOS digital line includes the Canon EOS 1100D, 100D, 600D, 650D, 700D, 60D, 60Da, 70D, 7D, 6D, 5D Mark III, and the 1D X. All Canon DSLRs with three- and four-digit model numbers, as well as the 7D, have APS-C sensors. The 6D, 5D series, and 1D X are full-frame. As of April 2013[update], all current Canon DSLRs use CMOS sensors.
- Nikon has a broad line of DSLRs, most in direct competition with Canon's offerings, including the D3100, D3200, D5100, D5200, D5300, D7000, D7100 and D300S with APS-C sensors, and the D600, D610, D800, D4, D3X and the Df with full-frame sensors.
- Leica produces the S2, which has a body similar to medium-sized DSLRs. However, in terms of sensor size and price, the camera is more like a medium-format camera.
- Pentax currently offers the K-3, K-50, and K-500, all of which use an APS-C sensor. These models 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). Pentax also offers the Pentax 645D, which is considered a medium format camera due to its larger sensor and compatibility with lenses made for Pentax's film medium-format cameras.
- 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. It currently offers the entry-level SD15 and the professional SD1. Sigma is the only DSLR manufacturer which sells lenses for other brands' lens mounts.
- Sony has discontinued its DSLRs in favor of single-lens translucent (SLT) cameras, which feature a fixed mirror that allows most light through to the sensor while reflecting some light to the autofocus sensor. Sony's SLTs feature full-time phase detection autofocus during video recording as well as continuous shooting of up to 12 frame/s. The α series, whether traditional SLRs or SLTs, offers in-body sensor-shift image stabilization and retains the Minolta AF lens mount. As of November 2013[update], the lineup included the Alpha 37, Alpha 57, Alpha 58, Alpha 65, the semipro Alpha 77, and the professional full-frame Alpha 99. The translucent (transmissive) fixed mirror, allows 70 percent of the light trough pass onto the imaging sensor and it means loss by 30 percent of light or a half stop loss, while 30 percent of the light is continuously reflected onto the camera's phase detection AF sensor makes fast autofocus for photo and video. This loss of light means that an optical viewfinder cannot be used; Sony SLT cameras instead use electronic viewfinders.
DSLRs compared to other digital cameras
The reflex design scheme is the primary difference between a DSLR and other digital camera. In the reflex design scheme, the image captured on the camera's sensor is also the image that is seen through the view finder. Light travels through a single lens and a mirror is used to reflect a portion of that light through the view finder – hence the name Single Lens Reflex. While there are variations among point-and-shoot cameras, the typical design exposes the sensor constantly to the light projected by the lens, allowing the camera's screen to be used as an electronic viewfinder. However, LCDs can be difficult to see in very bright sunlight.
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: it never provides an off-axis view. A disadvantage of the DSLR optical viewfinder system is that when it is used, it prevents using the LCD for viewing and composing the picture. Some people prefer to compose pictures on the display – for them this has become the de facto way to use a camera. 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 early DSLRs did not provide "live preview" (i.e., focusing, framing, and depth-of-field preview using the display), a facility that is always available on digicams. Today most DSLRs can alternate between live view and viewing through an optical viewfinder.
Optical view image and digitally created image
The larger, advanced digital cameras offer a non-optical electronic through-the-lens (TTL) view, via an eye-level electronic viewfinder (EVF) in addition to the rear LCD. The difference in view compared to a DSLR is that the EVF shows a digitally created image, whereas the viewfinder in a DSLR shows an actual optical 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. Optical viewfinders tend to be more comfortable and efficient, especially for action photography and in low-light conditions. Compared to digital cameras with LCD electronic viewfinders, 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 or sports photography, or any other situation where the subject or the camera is moving 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). An optical viewfinder may also cause less eye-strain. However, electronic viewfinders may provide a brighter display in low light situations, as the picture can be electronically amplified.
DSLR cameras often have image sensors of much larger size and often higher quality, offering lower noise, which is useful in low light. Although mirrorless digital cameras with sensors as large as APS-C size are now commonly available, larger sizes such as full frame and medium format sized image sensors are still mostly seen in DSLR designs, though full-frame compact cameras have been sporadically entering the market as of 2013.
DSLRs generally offer faster and more responsive performance, with less shutter lag, faster autofocus systems, and higher frame rates. Other digital cameras 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. Still, compact digital cameras are not suited for action, wildlife, sports and other photography requiring a high burst rate (frames per second).
Simple point-and-shoot cameras rely almost exclusively on their built-in automation and machine intelligence for capturing images under a variety of situations and offer no manual control over their functions, a trait which makes them unsuitable for use by professionals, enthusiasts and proficient consumers (aka "prosumers"). Bridge cameras provide some degree of manual control over the camera's shooting modes, and some even have hotshoes and the option to attach lens accessories such as filters and secondary converters. DSLRs typically provide the photographer with full control over all the important parameters of photography and have the option to attach additional accessories including hot shoe-mounted flash units, battery grips for additional power and hand positions, external light meters, and remote controls.
DSLRs have a larger focal length for the same field of view, which allows creative use of depth of field effects.However, small digital cameras can focus better on closer objects than typical DSLR lenses.
Fixed or interchangeable lenses
Unlike DSLRs, most digital cameras lack the option to change the lens. Instead, most compact digital cameras are manufactured with a zoom lens that covers the most commonly used fields of view. 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.
However, since the introduction of the Micro Four Thirds system by Olympus and Panasonic in late 2008, mirrorless interchangeable lens cameras are now widely available so the option to change lenses is no longer unique to DSLRs. Cameras for the micro four thirds system are designed with the option of a replaceable lens and accept lenses that conform to this proprietary specification. Cameras for this system have the same sensor size as the Four Thirds System but do not have the mirror and pentaprism, so as to reduce the distance between the lens and sensor.
Panasonic released the first Micro Four Thirds camera, the Lumix DMC-G1. 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. On 21 September 2011, Nikon announced with the Nikon 1 a series of high-speed MILCs. A handful of rangefinder cameras also support interchangeable lenses. Six digital rangefinders exist: 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, M9-P, M Monochrom and M (all full-frame cameras, with the Monochrom shooting exclusively in black-and-white).
In common with other interchangeable lens designs, DSLRs must contend with potential contamination of the sensor by dust particles when the lens is changed (though recent dust reduction systems alleviate this). Digital cameras with fixed lenses are not usually subject to dust from outside the camera settling on the sensor.
DSLRs generally have greater cost, size, and weight. They also have louder operation, due to the SLR mirror mechanism. Sony's fixed mirror design manages to avoid this problem. However, that design has the disadvantage that some of the light received from the lens is diverted by the mirror and thus the image sensor receives about 30% less light compared to other DSLR designs.
- Mirrorless interchangeable-lens camera
- Box camera
- Comparison of digital single-lens reflex cameras
- Digital photography
- Four Thirds System
- Full-frame digital SLR
- Panasonic – Lumix
- Photographic film
- Rangefinder camera
- Scheimpflug principle
- Single-lens reflex camera
- Single-lens translucent camera
- Twin-lens reflex camera
- Zeiss Ikon
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|Canon EOS digital SLR and MILC timeline (comparison)|
Naming of entry-level models: Rebel - Americas | Kiss - Japan
|Minolta/Konica Minolta/Sony DSLR and SLT A-mount timeline|
|Nikon DSLR timeline (comparison)|
|Olympus Four Thirds System Digital SLR timeline|
|Pentax Digital SLR timeline|
|Sigma Digital SLR timeline|
|Fujifilm F-mount DSLR timeline|