Mirrorless interchangeable-lens camera
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A mirrorless interchangeable lens camera (MILC) features a single, removable lens and uses a digital display system rather than an optical viewfinder. The word "mirrorless" indicates that the camera does not have an optical mirror or an optical viewfinder like a conventional Single Lens Reflex camera (SLR), but an electronic viewfinder which displays what the camera image sensor sees.  Like an SLR, an interchangeable lens mirrorless camera accepts any of a series of interchangeable lenses compatible with the lens mount of that camera. A mirrorless interchangeable lens camera is a further evolution from the film SLR camera, through the digital or DSLR camera, to a mirrorless system camera accepting interchangeable lenses, an MILC.
The biggest difference between a mirrorless interchangeable lens camera and a digital SLR or (DSLR) is that an electronic viewfinder or EVF is used to display what the image sensor sees as opposed to using a mirror-box, a movable mirror, a prism and an optical viewfinder or OVF which displays what the lens sees.  MILCs normally use a not so-accurate contrast-detect auto-focus, rather than the faster and precise phase-detect auto-focus used in DSLR cameras. 
Compared to DSLR cameras, mirrorless cameras are mechanically simpler and often smaller, lighter and quieter due to the elimination of the moving mirror for OVF viewing. Because of fewer moving parts the camera can also be more durable.
Since light metering and auto-focus are done on the image sensor, mirrorless cameras also don't need a secondary auto-focus mirror, nor a separate light metering sensor. Regarding the metering, a Mirrorless usually has no more than 250 metering photo-sensors (usually they have only 5) and a professional DSLR has more than one-hundred thousand RBG photo-sensors giving more precision to it.
Mirrorless cameras are still somewhat challenged to provide an EVF with the clarity and low-time-lag responsiveness of the OVFs used on DSLRs.. Furthermore, the contrast detect auto-focus (CDAF) used in mirrorless cameras, even when augmented by on-sensor phase detect auto-focus, tends to be marginally slower than that of phase detect auto-focus (PDAF) used by DSLRs. On the other hand, on-sensor auto-focus is more accurate and free of the adjustment requirements of the indirect but marginally faster focusing system of the DSLR. Also, the exposure rates possible with a mirror-less camera in first frame auto-focus mode, called single frame, is many times faster than that of a mirrored DSLR. However, photographing fast moving subjects in continuous auto-focus mode where the camera attempts to refocus for each frame, the high frame rate of the mirror-less camera will outpace its own auto-focus producing one or several out-of-focus frames between each in-focus frame, whereas the slower frame rate and faster auto-focus of a DSLR produces a higher percentage of in-focus exposures.
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Because of advances made in digital image sensor technology and electronic viewfinders, electronics are replacing most of the mechanics that were once necessary in DSLRs, resulting in less expensive and more reliable cameras. This has resulted in a shift in market shares which is likely to continue offering even more capable mirrorless cameras in the future.
One of the pioneers in the field has been Sony Corporation, which supplies a large number of other camera manufacturers with image sensors. Sony also sells cameras of their own, especially to show off advancements in their sensor and processing technology.
However, the large shift in the camera market in recent years have been toward smart phones with cameras. Both Canon and Nikon, the two biggest camera manufacturers, have lost sales and market shares in the overall photographic market as consumers have shifted toward buying mobile phones with built in cameras.
Other early players in the mirrorless system camera market are shown in the systems comparison below.
In 2013, mirrorless system cameras constituted about five percent of total camera shipments. In 2015, they accounted for 26 percent of system camera sales outside of the Americas, and 16 percent within the United States.
2004-2008. The first mirrorless camera commercially marketed was the Epson R-D1 (released in 2004), followed by the Leica M8 . The Micro Four Thirds system, whose first camera was the Panasonic Lumix DMC-G1, was released in Japan in October 2008.
2009-2010. The Ricoh GXR (November 2009) had a radically different design. The mirrorless camera featured interchangeable lens units – a sealed unit of a lens and sensor, instead of a normal interchangeable lens. This design was comparable to but distinct from MILCs, and received mixed reviews, primarily due to cost; As of 2017[update], the design has not been copied.
Following the introduction of the Micro Four Thirds, several other cameras were released by Panasonic and Olympus, with the Olympus PEN E-P1 (announced June 2009) being the first mirrorless camera in a compact size (pocketable with a small lens). The Samsung NX10 (announced January 2010) was the first camera in this class not using the Micro Four Thirds system, instead utilizing a new, proprietary lens mount (Samsung NX-mount). The Sony Alpha NEX-3 and NEX-5 (announced May 14, 2010, and released in July 2010) saw Sony enter the market with a new, proprietary lens mount (the Sony E-mount), though the camera included LA-EA1 and LA-EA2 adapters for the legacy Minolta A-mount.
2011. In June 2011, Pentax announced the 'Q' mirrorless interchangeable lens camera and the 'Q-mount' lens system. The original Q series featured a smaller 1/2.3 inch 12.4 megapixel CMOS sensor. The Q7, introduced in 2013, has a slightly larger 1/1.7 inch CMOS sensor with the same megapixel count.
In September 2011, Nikon announced their Nikon 1 system which consists of the Nikon 1 J1 and Nikon 1 V1 cameras and lenses. The V1 features an electronic viewfinder. The series includes high-speed mirrorless cameras which, according to Nikon, featured the world's fastest autofocus and the world's fastest continuous shooting speed (60 fps) among all cameras with interchangeable lenses including DSLRs.
2012. The Fujifilm X-Pro1, announced in January 2012, was the first non-rangefinder mirrorless with a built-in optical viewfinder. Its hybrid viewfinder overlaid electronic information, including shifting frame-lines, to compensate for the parallax effect. Its 2016 successor, the X-Pro2, features an updated version of this viewfinder.
Beyond just consumer interest, mirrorless lens systems has created significant interest from camera manufacturers as a possible alternative to high-end camera manufacturing. Mirrorless cameras has fewer moving parts than DSLRs, and are more electronic, which is an advantage to electronic manufacturers (such as Panasonic, Samsung and Sony), while reducing the advantage that existing camera manufacturers have in precision mechanical engineering. Sony's entry level full frame mirrorless α7 II camera has a 24 Megapixel 5 axis stabilised sensor but is more compact and lower in cost than any full frame sensor DSLR.
Canon was the last of the major manufacturer of DSLRs to announce their own mirrorless camera, announcing the Canon EOS M in 2012 with APS-C sensor and 18 mm registration distance similar to the one used by NEX.
In a longer-term Olympus decided that mirrorless may replace DSLRs entirely in some categories with Olympus America's DSLR product manager speculating that by 2012, Olympus DSLRs (the Olympus E system) may be mirrorless, though still using the Four Thirds System (not Micro Four Thirds).
Panasonic UK's Lumix G product manager John Mitchell, speaking to the Press at the 2011 "Focus on Imaging" show in Birmingham, reported that Panasonic "G" camera market share was almost doubling each year, and that the UK Panasonic "G" captured over 11% of all interchangeable camera sales in the UK in 2010, and that the UK "CSC" sales made up 23% of the interchangeable lens market in the UK, and 40% in Japan.
As of May 2010[update], the cost of interchangeable-lens camera is comparable to and somewhat higher than entry-level DSLRs, with costs between US$550 and $800, and significantly higher than the cost of high-end compact cameras.
Sony announced their 2011 sales statistics in September 2012, which showed that mirrorless lenses had 50% of the interchangeable lens market in Japan, 18% in Europe, and 23% worldwide. Since then, Nikon has entered the mirrorless market, amongst other new entries.
2013. Due to the downward trend of the world camera market, mirrorless camera sales suffered, but not as drastically and was compensated with increase by about 12 percent in the Japanese mirrorless camera market. However, mirrorless cameras have taken longer to catch on in Europe and North America. According to Japanese photo industry sources, mirrorless made up only 11.2% of interchangeable-lens cameras shipped to Europe in the first nine months of 2013, and 10.5% of those shipped to the U.S. in the same period. Also, an industry researcher determined that Mirrorless camera sales in the U.S. fell by about 20% in the three weeks leading up to December 14, 2013—which included the key Black Friday shopping week; in the same period, DSLR sales went up 1%.
2015. 2015 sales statistics showed that overall camera sales have fallen to one third of those of 2010, due to compact cameras being substituted by camera-capable mobile phones. Within camera sales, ILCs have seen their market share increasing, with ILCs being 30% of overall camera sales, of which DSLRs were 77% and mirrorless cameras were 23%. In the Americas in 2015, DSLR annual sales fell by 16% per annum, while mirrorless sales over the same 12-month period have increased by 17%.. In Japan, mirrorless cameras outsold DSLRs during some parts of the year. In 2015, mirrorless-cameras accounted for 26 percent of interchangeable-lens camera sales outside the Americas, although a lesser share of 26 percent was in the U.S.
2016. In late 2016, Olympus announced their OM-D E-M1 Mark II camera, a successor to the earlier and successful Mark I. The Mark II model retains a micro 4/3 image sensor of 17.3x13 mm and features a 20.4 megapixel resolution lens, representing a new generation of mirrorless cameras competitive with and in many respects superior to DSLR cameras.
|System||Notable models||Lens mount||Sensor size||Stabilization||Throat diameter||Flange focal distance||Focus system||35 mm equiv multiplier||Release date|
|Canon EOS M||Canon EOS M, EOS M2, EOS M3, EOS M10, EOS M5||Canon EF-M||22.3 × 14.9 mm APS-C||Lens-based||47 mm||18 mm||Hybrid Contrast-detection/Phase detection autofocus||1.6||October 2012|
|Fujifilm G||Fujifilm GFX 50S||Fujifilm G-mount||43.8 × 32.9 mm Medium format||Lens-based||??||26.7 mm||Contrast-detection autofocus||0.79||January 2017|
|Fujifilm XF||Fujifilm X-Pro1, X-T1, X-A1, X-M1, X-E1, X-A2, X-A10, X-A3, X-A5, X-E2, X-E3, X-T10, X-T20, X-Pro2, X-T2, X-H1||Fujifilm X-mount||23.6 × 15.6 mm APS-C||Lens-based
X-H1: Sensor-based (5-axis IBIS, 5.5 stops compensation)
|44 mm||17.7 mm||Hybrid Contrast-detection/Phase detection autofocus on X-H1, X-T1, X-T2, X-Pro2, X-T10, X-T20, X-E2, X-E3, X-A5; Contrast-detection autofocus on other models||1.5||January 2012|
|Hasselblad XCD||Hasselblad X1D||Hasselblad XCD mount||43.8 × 32.9 mm Medium format||none||??||20 mm||Contrast-detection autofocus||0.79||June 2016|
|Leica L||Leica T, SL||Leica L-mount||35.8×23.9 mm full-frame (SL)
23.6 × 15.7 mm APS-C (T)
|Lens-based||??||19 mm||Contrast-detection autofocus||1.0 (SL), 1.5 (T)||April 2014|
|Leica M (rangefinder camera)||Leica M8, M9, M9-P, M Monochrom, M-E, M; Epson R-D1, R-D1s, R-D1x, R-D1xG||Leica M-mount||35.8×23.9 mm full-frame (M9, M9-P, M Monochrom, M-E, and M), 27×18 mm half-frame (M8), 23.7×15.6 mm pseudo–APS-C (R-D1)||none||44 mm||27.80 mm||Rangefinder||1.0||March 2004 (R-D1)|
|Micro Four Thirds system||Panasonic Lumix DMC-G1, G10, G2, G3, GH1, GH2, GH3, GF1, GF2, GF3, GX1, GX7||Micro Four Thirds||17.3×12.98 mm 4/3||Lens-based (Panasonic); In body (Olympus)
Olympus EM-5 1st 5 axis stability system versus traditional 2 axis
|~38 mm||20 mm||Contrast-detection autofocus on most bodies; hybrid contrast-detection/phase detection autofocus on Olympus OM-D E-M1||2.0||October 2008 (G1)|
|Nikon 1||Nikon 1 J1, V1, J2, V2, J4, V3, J5||Nikon 1 mount||13.2 × 8.8 mm 1" Nikon CX||Lens-based||??||17 mm||Hybrid Contrast-detection/Phase detection autofocus||2.7||October 2011|
|Pentax K||Pentax K-01||Pentax K mount||23.6 × 15.6 mm APS-C||Sensor-based||??||45.46 mm||Contrast-detection autofocus||1.53||February 2012|
|Pentax Q||Pentax Q, Q10, Q7, Q-S1||Q-mount||6.17×4.55 mm (1/2.3") for Q and Q10
7.44×5.58 mm (1/1.7") for Q7 and Q-S1
|Sensor-based||38 mm||9.2 mm||Contrast-detection autofocus||5.5 (appx), Q and Q10
4.6 (appx), Q7 and Q-S1
|Ricoh GXR||Ricoh GXR||Sealed interchangeable sensor lens unit system, and Leica M-mount||Depends on each sealed interchangeable sensor lens unit: APS-C, 1/1.7", 1/2.3"||depends||—||—||Contrast-detection autofocus for sealed camera units, manual focus (display-assisted) for Leica M mount unit||1.5||November 2009|
|Samsung NX||Samsung NX10, NX100, NX200, NX20, NX300, NX30, NX500, NX1||Samsung NX-mount||23.4 × 15.6 mm APS-C||Lens-based||42 mm||25.5 mm||Hybrid Contrast-detection/Phase detection autofocus||1.53||January 2010|
|Sigma SA||Sigma SD Quattro, Sigma SD Quattro H||Sigma SA-mount||26.7 × 17.9 mm APS-H (Quattro H)
23.4 x 15.5 mm APS-C (Quattro)
|Lens-based||??||44 mm||Phase and contrast||1.35 (Quattro H)
|Sony α NEX||NEX-3, NEX-5, NEX-5N, NEX-6, NEX-7 (still cameras), NEX-VG10 (video camera)||Sony E-mount||23.4 × 15.6 mm APS-C||Lens-based||46.1 mm (1.815 inch)||18 mm||Contrast-detection autofocus (earlier models), Phase and Contrast (newer models)||1.5||June 2010|
|Sony α ILCE||α9, α7, α7R, α7S, α7 II, α7R II, α7S II, α7 III, α7R III, α6500, α6300, α6000, α5100, α5000, α3000||Sony E-mount||35.8×23.9 mm full-frame (α7 series and α9)
23.4 × 15.6 mm APS-C (αxx00)
|Depends (Lens-based, although α7 series II and III, plus α9, have 5-axis IBIS and can use lens and IBIS at same time)||46.1 mm (1.815 inch)||18 mm||Contrast-detection autofocus, Phase & Contrast (α7 series, α9, α6xxx)||1.0 (α7x and α9), 1.5 (αx000)||October 2013|
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