Introduction

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This is an historical summary and commentary of Nikon DSLRs. Click the links to individual reviews for details and comparisons.
A year in digital cameras is equal to 25 regular years. A camera introduced 2-1/2 years ago may as well be 62 years old. It's completely obsolete. A new D90 for $999 has far better image quality than the old Nikon D2Xs which sold for thousands the year before.
Contrast this to film cameras where my 4x5" Linhof Technika and 150mm lens are 50 years old, and still in the prime of their useful life.
This article reads backwards. The newest is on top.

Generations
There are vast differences in real image quality between Nikon's two generations of digital cameras.
Like most marketing organizations and repressive governments, camera makers keep most people in the dark by keeping them worrying about easy-to-understand things which make no difference, like pixels and ISOs which are easy to describe with just one number, instead of trying to teach people what really matters, which are the subtleties of how a picture actually looks.
Because camera makers have the masses worrying about pixels and bit depths, when Nikon makes significant advances, they're usually not obvious behind all the fluff.
The difference between generations is so significant that the best Gen 1 camera, the D2Xs, can't make pictures as good as the cheapest Gen 2 camera, the D90, in most real picture-taking situations.

First Generation
Nikon's first generation of digital SLRs started with the D1 of 1999 and continues in 2008 with the D40.
The first generation has only primitive picture and white balance adjustments.
Gen 1 cameras have an Optimize Image menu with crude controls allowing only two rudimentary options of "Enhance (+)" or "Moderate (-)" for saturation, and WB trims that extend only to ±3. There is no green/magenta adjustment for WB.
There were meaningless mentions of undefined modes I, II and III in the Optimize Image menu, but no clever dynamic range management as Gen 2 adds.
Gen 1 cameras are the D1 and D2 series, D40, D40x, D50, D70, D70s, D80, D100 and D200.

Second Generation
Nikon's second generation DSLRs started coming out in 2007 with the D3 and D300.
Second generation cameras offer the potential of significantly better real image quality because Gen 2 cameras add Nikon's Adaptive Dynamic Range (ADR).
Presuming its turned on, ADR allows Gen 2 cameras to render most real scenes much closer to the way our eyes see them, without all added contrast, blown highlights and blocked shadows common on film and Gen 1 cameras for most people.
If you're a pro who knows how, and actually controls his lighting perfectly, then you can get great results on Gen 1 cameras, but for most people who don't, Gen 2 cameras will give significantly better pictures.
The D90 has ADR on by default, and the D3, D700 and D300 need it turned on in the menus. I always shoot my cameras with ADR in NORMAL (or AUTO if available) for every shot.
Gen 2 cameras also are Nikon's first cameras to allow a full range of saturation and other image adjustments. Saturation and other values are set in direct units of up to ±3. These are set in the Picture Controls menus.
Gen 2 cameras have WB trims which extend 6 units in each direction, marked in blue and amber (not + and -) and allow green/magenta adjustment.
Gen 2 cameras offer five manual preset (gray card) WB storage settings, complete with icons and notes.
Gen 2 cameras magically and automatically correct color fringes caused by most lenses. If you're a tweaker, this alone significantly improves corner sharpness.

	The Gen 2 D90 is far, far better than the Gen 1 D200. I didn't have a D2Xs for comparison, but it would be the same as the D200. These shots are crops from the corner with the 18-200mm VR at 18mm. The D90 is as sharp as the D300. The D90 was focused elsewhere in this example.

Gen 2 cameras are using the increased in-camera processing horsepower to do all these tricks. If you're wasting your time shooting raw, you will have to hope that whatever software you're using to open raw files is as smart as what Nikon is building into these cameras for free. Many off-brands of software can't do any of this.
There was never much reason for raw, and in Gen 2, even less. It's quite likely that using raw with a Gen 2 camera and most, if not all, software, will throw you back into Gen 1 quality. It's not 2006 anymore. Most raw software does not do any of the clever things, like ADR, expanded color controls or totally automatic lens corrections, that are done in-camera.
Gen 2 cameras also have a super-sharp new 3" LCD screen.
Gen 2 cameras are the D3, D700, D300 and D90.
The D60 has ADR, but its stuck with the old Optimize Image menu and none of the other Gen 2 additions, so call it Gen 1.1 if you insist. I'm calling it Gen 1.
The D3000 has ADR and Gen II Picture Controls, but it has a crummier 3" LCD screen and does not correct lateral color fringes, so I'll call it Gen 1.5.
 
2010

Nikon D7000.

15 September 2010: Nikon D7000. 16MP DX, 6 FPS, 3" LCD, movies. $1,199.95, available mid-October 2010.
New in the D7000 is two SD card slots, Nikon's first 2,016-segment RGB meter, two new programmable mode-dial positions, U1 and U2 (as copied from Canon's C1 and C2 instant-recall settings), a 39-point AF system, and two types of Auto White Balance.

Nikon D3100.

19 August 2010: Nikon D3100. 14MP DX, 3 FPS, 3" LCD, movies. $699.95 with 18-55mm VR, available mid-September 2010.

2009

Nikon D3s.

14 October 2009: The Nikon D3s is just a mid-product-cycle freshening of the D3. Both are FX 12MP 9FPS cameras. Price is $5,200.
THe D3s adds video, a sensor cleaner, an additional 1.2x 8MP crop mode, dedicated INFO and Live View buttons, Quiet Mode, stupid-high ISOs to ISO 102,000, and $300 to the price of the D3.

Nikon D300s.

30 July 2009: The Nikon D300s adds movies, a dedicated INFO button and the QUIET mode to the D300.

Nikon D3000.

30 July 2009: The Nikon D3000 has a low-resolution 3" LCD and 10MP for $599, including an excellent 18-55mm VR lens. It's the worst Nikon DSLR ever made because it has very slow operation in most use, and has poor performance at high ISOs. The D40 of 2006 is superior and costs less.

Nikon D5000.

14 April 2009: The Nikon D5000 adds a flippy LCD screen, movies and 12MP DX for $730. It's slotted below the D90 but above the D40 from 2006.

2008

Nikon D3X.

01 December 2008: The D3X is annouced. It's identicle to the original D3, except with 24.4MP and only 5FPS and lower ISOs.
 

Nikon D90.

27 August 2008: The D90, a 12MP DX mid-line DSLR for $999. Replaces D80, and is a huge improvement over the D80 because it jumps to Gen 2.

Nikon D700.

01 July 2008: The D700, a 12MP FX DSLR for $2,999.95. It's Nikon's top amateur camera.

Nikon D60

January 28, 2008: Nikon D60 announced. Replaces D40x.

2007

Nikon D3

23 August 2007: The D300 and D3 are announced for November sale. Both have new 3" LCDs with live viewing.
The D3 is another milestone with Nikon's first 24x36mm sensor, dubbed FX. It runs 9FPS for $5,000. The D3 replaces the D2Xs. Nikon's press release on the D3.

Nikon D300

The D300 is an evolution of the D200, now with a 12MP DX sensor and 6-8 FPS for $1,800. $1,800 oddly is a price increase $300 over the D200. The D300 replaces the D200. Nikon's press release on the D300.

Nikon D40x

05 March 2007: The D40x is announced to fill a vacant price point in Nikon's line. It is the same as the excellent D40, but with 10MP instead of 6MP, but a slower sync speed of 1/200 vs. 1/500, a slower default ISO of 100 vs. 200, and a $200 higher price than the D40. The D40x was introduced to let Nikon fill in a price point in its camera line for competitive purposes. Personally I prefer the less expensive D40. See also the Megapixel Myth.

2006

Nikon D40

16 November 2006: The D40 is announced for Christmas at $599 with included excellent 18-55mm II lens. It is the smallest, lightest and least expensive Nikon DSLR ever. It started shipping on November 30th, 2006.

Nikon D80

09 August, 2006: The D80 is announced. 10 MP, 3 FPS for $999. The D80 is a D70 body and mechanics with the sensor and LCD of the D200.

Nikon D2Xs

June 2006: The D2Xs is announced, a slight improvement to the D2X. Same 12 MP and 5FPS and weird crop mode. $4,700.

2005

Nikon D200

01 November 2005: the D200 is announced. It's a groundbreaker at 10MP and 5 FPS at $1,699. It shipped in December 2005 as promised. It was on backorder until about October 2006. The D200 starts a new level in the Nikon line between the plastic D70 and the pro D2X.

Nikon D70s

Nikon D50

22 April 2005: The D70s and D50 are introduced. The D70s is a D70 with slightly larger screen. The D50 is a D70 with a couple of features removed. The D50 is still 6MP but only 2.5 FPS.
The D70, D70s and D50 are great cameras new or used, but replaced by the two-year-newer D80 of late 2006.

Nikon D2Hs

February, 2005: The D2Hs is announced. It's a minor revision of the D2H at a bargain price of $3,500. This makes a used D2H or new D2HS a great buy for sports. They are the same as the more expensive D2Xs, just faster with a few less pixels.

2004

Nikon D2X

16 September, 2004: the D2X is announced. 12MP, 5 FPS, $5,000. The D2X also has a bizarre cropped 7 MP, 8 FPS mode. Most of what the D2X does is replaced by the D200 in 2005. I'd get a used D2X if the price was right. It's Nikon's top of the line. I prefer the D200 for smaller size and a couple of more features.

Nikon D70

February 2004: Nikon shows the D70 at PMA. It's lightweight, 6MP, 3 FPS and a groundbreaker at $999. The D70 is a huge improvement over the D100 in almost every way except having no accessory vertical grip. All this, and it's priced less, too! The D70 fixes the dust problem by moving the CCD filter further away from the CCD. This throws dust out of focus and makes it much less of an annoyance than on the D1 series cameras.
The D70 replaced the D100.
Nikon was going to discontinue the D100, but instead decided to keep making the D100 because they discovered they could get a higher price than the D70 just because of the model number. People who equated price with quality kept buying D100s because they cost more.

2003
December, 2003: Nikon announced the development of the D70. Nikon had little to say other than the D70 would be cheap. Nikon was still inventing the D70 and had none to sell. Nikon made the announcement to get people to wait instead of fleeing from Nikon to Canon's inexpensive Digital Rebel.

Nikon D2H

22 July, 2003: The D2H is announced. 4.1 MP, 8 FPS, $5,000. The D2H was a new design with a much improved Li-Ion battery and a new flash exposure system. The D2H is a bargain used and a fantastic camera for sports.

2002

Nikon D100

21 February, 2002: The D100 is announced. It's 6 MP and 3 FPS for $1,999. This is Nikon's first lightweight amateur DSLR camera. It was an N80 with digital guts. It wasn't available for sale until June, 2002. It was a sellout with long waiting lists for a year after its introduction.
In May 2003 the D100 dropped to $1,699. In December 2003 it dropped to $1,499 where it stayed for a year or two. In May 2005 it dropped to $999.
Forget the D100, but snap one up if you can get a screaming deal.. The newer D70 and D50 work better. The D100 required messing with a wheel and knob to make critical adjustments. The newer cameras have direct entry buttons. The newer cameras have two years of extra wisdom in their firmware and just do everything better. Flash exposure isn't very good on the D100. See a comparison here. The D100 used the same EN-EL3 Li-Ion battery of the D50 and D70.

2001

Nikon D1H. Nikon D1X looks the same except for model number.

05 February 2001: Nikon announces the D1X and D1H, improvements to the D1. Performance was honed, a few features were added and price remained at $5,000.
They both replaced the numerical menu system with easy to understand menus in English.
The D1H kept the 2.7 MP sensor and increased speed to 5 FPS.
The D1X slowed to 3 FPS, but increased resolution to 5.3 MP. The resolution of the D1X is still decent in 2006. It used a bizarre CCD with twice the horizontal pixel density of the D1. Image quality was, and still is, extremely good because it had 4,024 horizontal pixels on the CCD. It had to do less Bayer interpolation and thus has much better image quality than one would expect in its 3,008 x 2,000 pixel images.
Don't buy either of these today regardless of price. They had awful battery systems. I had a D1H. They only run for about 250 shots on a charge. The batteries are huge, heavy Ni-MH packs which require constant babying in charging. The packs have protuberances which make them painful to carry in a pocket. They lose charge if left unused. Even a freshly charged battery would indicate almost dead after a few shots. Most D1, D1H and D1X users including myself lived with the viewfinder indications turning off, indicating almost dead battery, after just a few shots. They also had awful flash exposure. Many photographers had to revert to non-TTL exposure modes because the TTL mode was so flaky. Dust was a horrible problem because the CCD cover filter was too close to the CCD. At almost any aperture you'd see dust clearly on the image. They were state of the art in their era (2001 - 2003), but that era is long gone.

1999:World's First Practical DSLR

Nikon D1

15 February 1999: Nikon announced it was working on "a new professional class, high-quality digital Single Lens Reflex Camera."
15 June, 1999: Nikon announces the D1, the world's first practical DSLR. It is the first practical DSLR because it's the first DSLR with good enough image quality for print (2.7 MP), fast enough (4.5 FPS) and priced low enough ($5,000) and functional enough to be sensible to use daily as a primary camera. It's also the first DSLR made with Nikon electronics in a Nikon body, by Nikon.
It replaced film at forward-looking newspapers.
Forget about it today, regardless of price. For the same price you can get the greatly improved D1H or D1X, neither of which are worthwhile today either. The D1 is confined to the dumpster of history (and collectors) because its battery system is a pain, and its menu structure requires interpreting numerical custom functions. It requires a cheat sheet to decipher. Flash exposure performance is awful. Get one only as a landmark camera to collect. The D1 is the landmark. The D1 is the camera that replaced film at newspapers.
The D1 is unique in having a 1/16,000 top shutter speed, since its shutter is also electronic. That's how oit gets a 1/500 sync speed. If you use the PC sync terminal or a non-dedicated flash so the D1 doens't know you've got a flash attached; sync goes all the way to 1/16,000!
Nikon announced no new DSLRs for a couple of years.

1998
The similar E3 and E3S came out, still based on a big klunky Fuji body. They were still only 1.3 MP (1,280 x 1,000 pixels). SCSI interface. Still about $20,000.
These relics are worth about $300 in 2006. Don't bother using them for serious photography.

1996
A minor upgrade, the E2N and E2NS came out and was still about $20,000.
These relics are worth about $300 in 2006. Don't bother using them for serious photography.

1995
Digital SLRs are still science experiments, but in series production for special events. Nikon finally makes its first commercialized DSLR, over twenty years after America invented digital cameras.
It was called the Nikon E2 and E2S. They weren't Nikon bodies at all. They were hacked out of Fuji bodies with Nikon electronics! Bizarre internal reduction optics helped restore the field of view, with weird effective apertures. PCMCIA card memory. About $20,000 and only 1.3 megapixels, which is why they don't count as practical cameras.
These relics are worth about $300 in 2006. Don't bother using them for serious photography.

1991
Digital SLRs are still custom built laboratory experiments. NASA had some Texans hack an F4 to fly on the STS-48 shuttle mission. It had a 1MP black-and-white sensor and recorded to a Texas-sized hard drive hacked to the bottom of the F4. See it here. Nikon had nothing to do with this as far as I know. It was the Texans who played Frankenstein with a stock F4 body.
Kodak sold the $13,000 1.3 MP DCS-100, hacked into an F3HP body.

1990
Kodak shows a hacked Nikon body with a Kodak sensor at Photokina called the DCS. It was 1 MP and cost $25,000. It shipped in 1991.
Kodak kept trying through about 2003, and gave up after the 14n.
These and later model Kodaks were popular for some news events, but most newspapers that had them threw them away when the D1 came out in 1999.

1973
Kodak created the first digital camera in Rochester, New York, USA. It was big and scary and certainly didn't run on batteries. Nikon had nothing to do with this, although Kodak probably used a Nikkor lens.
More Information: This site also has an excellent history of digital Nikons.
                                                                                                                                                               Source: Kenrockwell.com

Compact digital cameras

Subcompact with lens assembly retracted

Compact cameras are designed to be tiny and portable and are particularly suitable for casual and "snapshot" use, thus are also called point-and-shoot cameras. The smallest, generally less than 20 mm thick, are described as subcompacts or "ultra-compacts" and some are nearly credit card size.^[2]
Most, apart from ruggedized or water-resistant models, incorporate a retractable lens assembly allowing a thin camera to have a moderately long focal length and thus fully exploit an image sensor larger than that on a camera phone, and a mechanized lens cap to cover the lens when retracted. The retracted and capped lens is protected from keys, coins and other hard objects, thus making a thin, pocketable package. Subcompacts commonly have one lug and a short wrist strap which aids extraction from a pocket, while thicker compacts may have two lugs for attaching a neck strap.
Compact cameras are usually designed to be easy to use, sacrificing advanced features and picture quality for compactness and simplicity; images can usually only be stored using lossy compression (JPEG). Most have a built-in flash usually of low power, sufficient for nearby subjects. Live preview is almost always used to frame the photo. Most have limited motion picture capability. Compacts often have macro capability and zoom lenses but the zoom range is usually less than for bridge and DSLR cameras. Generally a contrast-detect autofocus system, using the image data from the live preview feed of the main imager, focuses the lens.
Typically, these cameras incorporate a nearly-silent leaf shutter into their lenses.
For lower cost and smaller size, these cameras typically use image sensors with a diagonal of approximately 6 mm, corresponding to a crop factor around 6. This gives them weaker low-light performance, greater depth of field, generally closer focusing ability, and smaller components than cameras using larger sensors.

A digital camera (or digicam) is a camera that takes video or still photographs, or both, digitally by recording images via an electronic image sensor. Most 21st century cameras are digital.^[1]

Front and back of Canon PowerShot A95

Digital cameras can do things film cameras cannot: displaying images on a screen immediately after they are recorded, storing thousands of images on a single small memory device, and deleting images to free storage space. The majority, including most compact cameras, can record moving video with sound as well as still photographs. Some can crop and stitch pictures and perform other elementary image editing. Some have a GPS receiver built in, and can produce Geotagged photographs.
The optical system works the same as in film cameras, typically using a lens with a variable diaphragm to focus light onto an image pickup device. The diaphragm and shutter admit the correct amount of light to the imager, just as with film but the image pickup device is electronic rather than chemical.
Digital cameras are incorporated into many devices ranging from PDAs and mobile phones (called camera phones) to vehicles. The Hubble Space Telescope and other astronomical devices are essentially specialized digital cameras.

Advantages

Many of the advantages of SLR cameras derive from viewing and focusing the image through the attached lens. Most other types of cameras do not have this function; subjects are seen through a viewfinder that is near the lens, making the photographer's view different from that of the lens. SLR cameras provide photographers with precision; they provide a viewing image that will be exposed onto the negative exactly as it is seen through the lens. There is no parallax error, and exact focus can be confirmed by eye — especially in macro photography and when photographing using long focus lenses. The depth of field may be seen by stopping down to the attached lens aperture, which is possible on most SLR cameras except for the least expensive models. Because of the SLR's versatility, most manufacturers have a vast range of lenses and accessories available for them.
Compared to most fixed-lens compact cameras, the most commonly used and inexpensive SLR lenses offer a wider aperture range and larger maximum aperture (typically f/1.4 to f/1.8 for a 50 mm lens). This allows photographs to be taken in lower light conditions without flash, and allows a narrower depth of field, which is useful for blurring the background behind the subject, making the subject more prominent. 'Fast' lenses are commonly used in theater photography, portrait photography, surveillance photography, and all other photography requiring a large maximum aperture.
The variety of lenses also allows for the camera to be used and adapted in many different situations. This provides the photographer with considerably more control (i.e., how the image is viewed and framed) than would be the case with a view camera. In addition, some SLR lenses are manufactured with extremely long focal lengths, allowing a photographer to be a considerable distance away from the subject and yet still expose a sharp, focused image. This is particularly useful if the subject includes dangerous animals (e.g., wildlife); the subject prefers anonymity to being photographed; or else, the photographer's presence is unwanted (e.g., celebrity photography or surveillance photography). Practically all SLR and DSLR camera bodies can also be attached to telescopes and microscopes via an adapter tube to further enhance their imaging capabilities

Disadvantages

In most cases, single-lens reflex cameras cannot be made as small or as light as other camera designs — such as rangefinder cameras, autofocus compact cameras and digital cameras with electronic viewfinders (EVF) — owing to the mirror box and pentaprism/pentamirror. The mirror box also prevents lenses with deeply-recessed rear elements from being mounted close to the film or sensor unless the camera has a mirror lockup feature; this means that simple designs for wide angle lenses cannot be used. Instead, larger and more complex retrofocus designs are required.

During an exposure the viewfinder is blocked

The SLR mirror 'blacks-out' the viewfinder image during the exposure. In addition, the movement of the reflex mirror takes time, limiting the maximum shooting speed. The mirror system can also cause noise and vibration. Partially-reflective (pellicle) fixed mirrors avoid these problems and have been used in a very few designs including the Canon Pellix and the Canon EOS-1N RS, but these designs introduce their own problems. These pellicle mirrors reduce the amount of light travelling to the film plane or sensor and also can distort the light passing through them, resulting in a less-sharp image. To avoid the noise and vibration, many professional cameras offer a mirror lock-up feature, however, this feature totally disables the SLR's automatic focusing ability. Electronic viewfinders have the potential to give the 'viewing-experience' of a DSLR (through-the-lens viewing) without many of the disadvantages.

 Reliability of SLRs

SLRs vary widely in their construction and typically have bodies made of plastic or magnesium. Most manufacturers don't cite durability specifications, but some report shutter life expectancies for professional models. For instance, the Canon EOS 1Ds MkII is rated for 200,000 shutter cycles and the newer Nikon D3 is rated for 300,000 with its exotic carbon fiber/kevlar shutter. Because many SLRs have interchangeable lenses, there is a tendency for dust, sand and dirt to get into the main body of the camera through the mirror box when the lens is removed, thus dirtying or even jamming the mirror movement mechanism or the shutter curtain mechanism itself. In addition, these particles can also jam or otherwise hinder the focusing feature of a lens if they enter into the focusing helicoid. The problem of sensor cleaning has been somewhat reduced in DSLRs as some cameras have a built-in sensor cleaning unit.

The Contaflex III a single-lens reflex camera from West Germany from 1957, with additional 115 mm lens	The 1952 (Pentax) Asahiflex, Japan's first single-lens reflex camera	The 35 mm film-based Nikon F, 1959, the world's first system camera	Olympus The 35 mm film-based Olympus OM-2, which was the first SLR to measure light for electronic flash at the shutter curtain.
The Pentax Spotmatic IIa	Nikon F5 professional SLR	Digital SLR Nikon D200 and a Nikon film scanner	Medium format SLR by Hasselblad

Large format SLR cameras were probably first marketed with the introduction of C.R. Smith's Monocular Duplex (USA, 1884).^[2] SLRs for smaller exposure formats were launched in the 1920s by several camera makers. The first 35 mm SLR available to the mass market, Leica's PLOOT reflex housing along with a 200mm f4.5 lens paired to a 35mm rangefinder camera body, debuted in 1935. The Soviet Спорт (“Sport”)^[3], also a 24mm by 36mm image size, was prototyped in 1934 and went to market in 1937. K. Nüchterlein's Ihagee Kine-Exakta (Germany, 1936) was the first integrated 35mm SLR to enter the market. AdditionalExakta models, all with waist-level finders, were produced up to and during World War II. Another ancestor of the modern SLR camera was the Swiss-made Alpa, which was innovative, and influenced the later Japanese cameras. The first eye-level SLR viewfinder was patented in Hungary on August 23, 1943 by Jenő Dulovits, who then designed the first 35 mm camera with one, the Duflex, which used a system of mirrors to provide a laterally correct, upright image in the eye-level viewfinder. The Duflex, which went into serial production in 1948, was also the world's first SLR with an instant-return (a.k.a. autoreturn) mirror.
The first commercially produced SLR that employed a roof pentaprism was the Zeiss Ikon VEB Contax S, announced on May 20, 1949.
The Japanese adopted and further developed the SLR. In 1952, Asahi developed the Asahiflex and in 1954, the Asahiflex IIB. In 1957, the Asahi Pentax combined the fixed pentaprism and the right-hand thumb wind lever. Nikon, Canon and Yashica introduced their first SLRs in 1959 (the F, Canonflex, and Pentamatic, respectively).

[edit] Through-the-lens light metering

As a small matter of history, the first 35 mm camera (non-SLR) to feature through the lens light metering may have been Nikon, with a prototype rangefinder camera, the SPX. According to the below website, the camera used Nikon 'S' type rangefinder lenses.^[4]
Through-the-lens light metering is also known as "behind-the-lens metering". In the SLR design scheme, there were various placements made for the metering cells, all of which used CdS (Cadmium sulfide) photocells. The cells were either located in the pentaprism housing, where they metered light transmitted through the focusing screen; underneath the reflex mirror glass itself, which was Topcon's design; or in front of the shutter mechanism, which was the design used by Canon with their Canon Pellix.
Pentax was the first manufacturer to show an early prototype 35 mm behind-the-lens metering SLR camera, which was named the Pentax Spot Matic. The camera was shown at the 1960 Photokina show. However, the first Through-the-lens (TTL) light metering SLR on the market was the 1963 Topcon RE Super, which had the CdS metering cell placed behind the reflex mirror. The mirror had narrow slits cut into the surface to let the light reach the cell providing average metering. Late in the following year, a production model of the Pentax Spotmatic was shown whose CdS light meter cells were on the pentaprism , reading the light off the focusing screen providing average reading, yet keeping the Spotmatic name, but now written in one word. Another clever design appeared in 1965, the Canon Pellix employing a pellicle mirror that is semi-transparent, placing the meter cell on an arm swinging into the lightpass behind the mirror for meter reading.
Mamiya Sekor came out with cameras such as the Mamiya Sekor TL and various other versions. Yashica introduced the TL Super. Both of these cameras used M42 screw thread lenses as did the Pentax Spotmatic. Later on Fujica introduced their ST-701, then ST-801 and ST-901 cameras. The ST-701 was the first SLR to use a silicon cell photodiode, which was more sensitive than CdS and was immune to the memory effect that the CdS cell suffered from in bright sunlight. Gradually, other 35 mm SLR camera manufacturers changed their behind-the-lens meters from CdS cells to Silicon Diode photocells.
Other manufacturers responded and introduced their own behind-the-lens metering cameras. Nikon and Miranda, at first, simply upgraded their interchangeable pentaprisms to include behind-the-lens metering (for Nikon F, and Miranda D, F, Fv and G models) and these manufacturers also bought out other camera models with built-in behind-the-lens metering capability, such as the Nikkormat FT and the Miranda Sensorex (which used an external coupling diaphragm). Minolta introduced the SRT-101, which used Minolta's proprietary system they referred to as "CLC", which was an acronym for "contrast light compensation", which metered differently from an average metering behind-the-lens camera.
Some German manufacturers also introduced cameras such as the Zeiss Ikon Contarex family, which was one of very few 35 mm SLR to use interchangeable film backs.
Inexpensive leaf-shutter cameras also benefited from behind-the-lens metering as, Topcon introduced the Auto 100 with front-mount interchangeable lenses designed only for that camera, and one of the Zeiss Ikon Contaflex leaf shutter cameras. Kowa manufactured their SET-R, which had similar specifications.
Within months, manufacturers decided to bring out models that provided limited area metering, such as Nikon's Photomic Tn finder, which concentrated 60% of the CdS cells sensitivity on the inner circle of the focusing screen and 30% on the surrounding area. Canon used spot metering in the unusual Canon Pellix camera, which also had a stationary mirror system that allowed approximately 70% of the light to travel to the film plane and 30% to the photographer's eye. This system, unfortunately, degraded the native resolution of the attached lens and provided less illumination to the eyepiece. It did have the advantage of having less vibration than other SLR cameras but this was not sufficient to attract professionals to the camera in numbers.

Single-lens reflex camera

The historic 1949 Zeiss Ikon VEB Contax S, manufactured in Dresden, the first pentaprism SLR for eye-level viewing

A single-lens reflex (SLR) camera is a camera that typically uses a semi-automatic moving mirror system that permits the photographer to see exactly what will be captured by the film or digital imaging system (after a very small delay), as opposed to pre-SLR cameras where the view through the viewfinder could be significantly different from what was captured on film. (The Canon Pellix film camera was an exception wherein the mirror was a fixed beamsplitting pellicle.)
Prior to the development of SLR, all cameras with viewfinders had two optical light paths: one path through the lens to the film, and another path positioned above (TLR or twin-lens reflex) or to the side (rangefinder). Because the viewfinder and the film lens cannot share the same optical path, the viewing lens is aimed to intersect with the film lens at a fixed point somewhere in front of the camera. This is not problematic for pictures taken at a middle or longer distance, but parallax causes framing errors in close-up shots. Moreover, focusing the lens of a fast reflex camera when it is opened to wider apertures (such as in low light or while using low-speed film) is not easy.
Most SLR cameras permit upright and laterally correct viewing through use of a pentaprism situated in the optical path between the reflex mirror and viewfinder. Light is reflected by a movable mirror upwards into the pentaprism where it is reflected several times until it aligns with the viewfinder. When the shutter is released, the mirror moves out of the light path, and the light shines directly onto the film (or in the case of a DSLR, the CCD or CMOS imaging sensor).
Focus can be adjusted manually by the photographer or automatically by an autofocus system. The viewfinder can include a matte focusing screen located just above the mirror system to diffuse the light. This permits accurate viewing, composing and focusing, especially useful with interchangeable lenses.
Up until the 1990s, SLR was the most advanced photographic preview system available, but the recent development and refinement of digital imaging technology with an on-camera live LCD preview screen has overshadowed SLR's popularity. Nearly all inexpensive compact digital cameras now include an LCD preview screen allowing the photographer to see what the CCD is capturing. However, SLR is still popular in high-end and professional cameras because they are system cameras with interchangeable parts, allowing customization. They also have far less shutter lag, allowing photographs to be timed more precisely. Also the pixel resolution, contrast ratio, refresh rate, and color gamut of an LCD preview screen cannot compete with the clarity and shadow detail of a direct-viewed optical SLR viewfinder

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^[update], 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 K-7

• 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 (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.

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.

DSLR lenses

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

Nikon AF Nikkor 18-70mm DX Zoom lens

Main articles: Photographic lens and Lenses for SLR and DSLR cameras

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

Further information: crop factor

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.