Digital single-lens reflex camera

Digital single-lens reflex camera

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. (Note that the diagram below incorrectly shows a non-roof pentaprism.) During exposure, the mirror assembly swings upward, the aperture narrows (if stopped down, or set smaller than wide open), and a shutter opens, allowing the lens to project light onto the image sensor. A second shutter then covers the sensor, ending the exposure, and the mirror lowers while the shutter resets. The period that the mirror is flipped up is referred to as “viewfinder blackout”. A fast-acting mirror and shutter is preferred so as to not delay an action photo.
All of this happens automatically over a period of milliseconds, with cameras designed to do this 3–10 times 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. [source:wiki]

 

Working Mechanism of DSLR

DSLR design principles

Cross-section view of DSLR system:
  1. 4-element lens
  2. Reflex mirror
  3. Focal-plane shutter
  4. Image sensor
  5. Matte focusing screen
  6. Condenser lens
  7. Pentaprism
  8. Eyepiece

Cutaway of an Olympus E-30 DSLR

A DSLR cutaway diagram

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.[1] 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.

Dslr history

History

On August 25, 1981 Sony unveiled a prototype of the first still video camera, the Sony Mavica. This camera was an analog electronic camera that featured interchangeable lenses and a SLR viewfinder.
At Photokina in 1986, Nikon revealed a prototype analog electronic still SLR camera, the Nikon SVC, a precursor to the digital SLR.[25] The prototype body shared many features with the N8008.[25]
In 1991, Kodak released the first commercially available digital SLR, the Kodak DCS-100. It consisted of a modified Nikon F3 SLR body, modified drive unit, and an external storage unit connected via cable. The 1.3 megapixel camera cost approximately US$30,000. This was followed by the Kodak DCS-200 with integrated storage.[26]
Over the next decade, DSLRs have been released by various companies, including Canon, Nikon, Kodak, Pentax, Olympus, Panasonic, Samsung, Minolta (later Konica Minolta, and whose camera assets were then acquired by Sony), Fujifilm, and Sigma, with higher resolutions and lower prices.
In 1999, Nikon announced the Nikon D1, the first DSLR to truly compete with, and begin to replace, film cameras in the professional photojournalism and sports photography fields. This camera was able to use current autofocus Nikkor lenses available at that time for the Nikon film series cameras, and was also able to utilize the older Nikon and similar, independent mount lenses designed for those cameras. A combination of price, speed, and image quality was the beginning of the end of 35 mm film for these markets.
In January 2000, Fujifilm announced the FinePix S1 Pro, the first DSLR marketed to non-professionals.
In November 2001, Canon released its 4.1 megapixel EOS-1D, the brand’s first professional digital body.
In 2003, Canon introduced the 6.3 megapixel EOS 300D SLR camera (known in the United States as the Digital Rebel and in Japan as the Kiss Digital) with an MSRP of US$999, directed at the consumer market. Its popularity encouraged other manufacturers to produce affordable digital SLR cameras, lowering entry costs and allowing more amateur photographers to purchase DSLRs.
In 2004 Konica Minolta released Konica Minolta Maxxum 7D, first DSLR with in-body image stabilization[27] 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 first sub-2000 USD full frame DSLR, the Sony Alpha 850, creating first 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

As of 2008, 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.[28] In the Japanese domestic market, Nikon captured 43.3% to Canon’s 39.9%, with Pentax a distant third at 6.3%.[29]
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, Fujifilm, Leica, Nikon, Olympus, Panasonic, 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 EOS digital line includes the 1000D,[30] 450D,[30] 50D, 5D Mark II, and the 1Ds Mark III. Canon’s latest cameras, the 500D, 7D, and 1D Mark IV were introduced in 2009, while the 550D and 60D were introduced in 2010. As of January 2010, all current Canon DSLRs use CMOS sensors.
  • Fujifilm currently sells 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, D5000, D90, D7000, D300S, D700, D3S and the D3X. The D3, announced in August 2007, is the company’s first full-frame digital SLR.[31]
  • Olympus makes DSLR cameras and lenses as part of the Four Thirds System. Current Olympus models include the E-620, E-30 and E-3. 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.[32][33]
  • Pentax currently offers the Pentax K-5, Pentax K-7, Pentax K-x, Pentax K-r and the medium format Pentax 645D,[34] 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 continious shooting of up to 10 fps. 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 (6×4.5 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[35] (and often higher-quality) lenses.
  • Image sensors of much larger size and often higher quality, offering lower noise,[36][37] 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.[38]
  • The larger focal length for the same field of view allows creative use of depth of field[39] effects.
  • Ability to attach additional accessories[40] 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:

 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 aren’t 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[45] 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. The new system shares the same sensor size as the original Four Thirds System, but does not use a mirror system and is therefore able to reduce the focal-distance between the lens and sensor. Micro Four Thirds cameras substitute an electronic viewfinder with the same eye level relief, mimicking the viewfinder operation of DSLRs. All four thirds cameras also 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.

DSLR Lenses

DSLR lenses

Nikon AF Nikkor 50mm full frame (FX) Prime lens

Nikon AF Nikkor 18-70mm DX Zoom lens

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 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[8] 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.

History

On August 25, 1981 Sony unveiled a prototype of the first still video camera, the Sony Mavica. This camera was an analog electronic camera that featured interchangeable lenses and a SLR viewfinder.
At Photokina in 1986, Nikon revealed a prototype analog electronic still SLR camera, the Nikon SVC, a precursor to the digital SLR.[25] The prototype body shared many features with the N8008.[25]
In 1991, Kodak released the first commercially available digital SLR, the Kodak DCS-100. It consisted of a modified Nikon F3 SLR body, modified drive unit, and an external storage unit connected via cable. The 1.3 megapixel camera cost approximately US$30,000. This was followed by the Kodak DCS-200 with integrated storage.[26]
Over the next decade, DSLRs have been released by various companies, including Canon, Nikon, Kodak, Pentax, Olympus, Panasonic, Samsung, Minolta (later Konica Minolta, and whose camera assets were then acquired by Sony), Fujifilm, and Sigma, with higher resolutions and lower prices.
In 1999, Nikon announced the Nikon D1, the first DSLR to truly compete with, and begin to replace, film cameras in the professional photojournalism and sports photography fields. This camera was able to use current autofocus Nikkor lenses available at that time for the Nikon film series cameras, and was also able to utilize the older Nikon and similar, independent mount lenses designed for those cameras. A combination of price, speed, and image quality was the beginning of the end of 35 mm film for these markets.
In January 2000, Fujifilm announced the FinePix S1 Pro, the first DSLR marketed to non-professionals.
In November 2001, Canon released its 4.1 megapixel EOS-1D, the brand’s first professional digital body.
In 2003, Canon introduced the 6.3 megapixel EOS 300D SLR camera (known in the United States as the Digital Rebel and in Japan as the Kiss Digital) with an MSRP of US$999, directed at the consumer market. Its popularity encouraged other manufacturers to produce affordable digital SLR cameras, lowering entry costs and allowing more amateur photographers to purchase DSLRs.
In 2004 Konica Minolta released Konica Minolta Maxxum 7D, first DSLR with in-body image stabilization[27] 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 first sub-2000 USD full frame DSLR, the Sony Alpha 850, creating first 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.