History of the single-lens reflex camera

The history of the single-lens reflex camera (SLR) begins with the use of a reflex mirror in a camera obscura described in 1676, but it took a long time for the design to succeed for photographic cameras. The first patent was granted in 1861, and the first cameras were produced in 1884, but while elegantly simple in concept, they were very complex in practice. One by one these complexities were overcome as optical and mechanical technology advanced, and in the 1960s the SLR camera became the preferred design for many high-end camera formats.
The advent of digital point-and-shoot cameras in the 1990s through the 2010s with LCD viewfinder displays reduced the appeal of the SLR for the low end of the market. The mirrorless interchangeable-lens camera is increasingly challenging the mid-price range market. But the SLR remains the camera design of choice for most professional and ambitious amateur photographers.
Early large and medium format SLRs.
The photographic single-lens reflex camera (SLR) was invented in 1861 by Thomas Sutton, a photography author and camera inventor who ran a photography related company together with Louis Désiré Blanquart-Evrard on Jersey. Only a few of his SLRs were made. The first production SLR with a brand name was Calvin Rae Smith's Monocular Duplex (USA, 1884). Other early SLR cameras were constructed, for example, by Louis van Neck (Belgium, 1889), Thomas Rudolphus Dallmeyer (England, 1894) and Max Steckelmann (Germany, 1896), and Graflex of the United States and Konishi in Japan produced SLR cameras as early as 1898 and 1907 respectively. These first SLRs were large format cameras. While SLR cameras were not very popular at the time, they proved useful for some work. These cameras were used at waist level; the ground glass screen was viewed directly, using a large hood to keep out extraneous light. In most cases, the mirror had to be raised manually as a separate operation before the shutter could be operated.
As with camera technology in general, SLR cameras became available in smaller and smaller sizes. Medium format SLRs soon became common, at first larger box cameras and later "pocketable" models such as the Ihagee Vest-Pocket Exakta of 1933.
Development of the 35 mm SLR.
The first 35mm prototype SLR was the "Filmanka" developed in 1931 by A. Min in the Soviet Union. In 1933 A.O. Gelgar developed the "GelVeta" also in the USSR, later re-named "Спорт" ("Sport"). "Sport" was a very smart design with a 24mm × 36mm frame size, but, according to some sources, it did not enter the market until 1937, although there is now some evidence emerging that "Sport" may have been in limited production before 1936. 
Therefore, it is claimed not to be the first mass produced 35mm SLR.
Early innovations.
Early 35 mm SLR cameras had functionality that was similar to larger models, with a waist-level ground-glass viewfinder and a mirror that remained in the taking position and blacked out the viewfinder after an exposure, and then returned when the film was wound on. Innovations that transformed the SLR were the pentaprism eye-level viewfinder and the instant-return mirror—the mirror flipped briefly up during exposure, immediately returning to the viewfinding position. The half-silvered fixed pellicle mirror, without even the brief blackout of the instant-return mirror, was also innovative but did not become standard. Through-the-lens light metering was another important advance. As electronics advanced, new functionality, discussed below, became available.
Exakta.
The first 35mm format SLR in large scale production was the Ihagee Kine Exakta, produced in 1936 in Germany, which was fundamentally a scaled-down Vest-Pocket Exakta. This camera used a waist-level finder.
Various other models were produced, such as the Kine-Exakta, the Exakta II, the Exakta Varex (featuring an interchangeable pentaprism eye-level viewfinder and identified in the United States as the 'Exakta V'), the Exakta Varex VX (identified in the United States as the 'Exakta VX'), the Exakta VX IIa, the Exakta VX IIb, the Exakta VX500 and the Exakta VX1000. Ihagee also manufactured less expensive cameras under the 'Exa' camera label, such as the Exa, the Exa Ia, the Exa II, the Exa IIa, the Exa IIb (which was generally not considered part of the "official" Exa line), and the Exa 500. The Exacta sold well and triggered other camera manufacturers to develop 35mm SLRs. Sales were particularly strong in the medical and scientific fields. A large range of lenses and accessories were made by a variety of manufacturers, turning the camera into one of the first system cameras, although motor drives and bulk loading backs were never produced by Ihagee.
Rectaflex.
Rectaflex was the name of an Italian camera maker from 1947 to 1958. It was also the name of their sole model. The Rectaflex was a 35 mm SLR camera with a focal plane shutter, interchangeable lenses, and a pentaprism eye-level finder. Rectaflex (followed by Contax S) was the first SLR camera introducing the modern pentaprism eye-level finder. The first prototype (Rectaflex 947) was presented in 1947, with a final presentation in April 1948 and start of series production (A 1000) in September the same year, thus hitting the market one year before the Contax S, presented in 1949. Both were preceded by Alpa-Reflex, first presented to a wider public in April 1944 at the Swiss Trade Fair in Basel (Schweizer Mustermesse). Alpa’s production was slow up to 1945, and it lacked a pentaprism, so the image was reversed left-to-right.
Zeiss.
Zeiss had begun work on a 35mm SLR camera in 1936 or 1937. This camera used an eye-level pentaprism, which allowed eye-level-viewing of an image oriented correctly from left to right. Waist-level finders, however, showed a reversed image, which the photographer had to mentally adjust for while composing the image by looking downward and viewing and focusing. To brighten the viewfinder image, Zeiss incorporated a fresnel lens inbetween the ground-glass screen and the pentaprism. This design principle became the conventional SLR design used today.
World War II intervened, and the Zeiss SLR did not emerge as a production camera until Zeiss, in the newly created factory in East Germany, introduced the Contax S in 1949, with production ending in 1951. The Italian Rectaflex, series 1000 went into series production the year before, in September 1948, thus being market-ready one year before the Contax. Both were historic progenitors of many later SLRs that adopted this arrangement.
Praktiflex Praktica.
In 1939, Kamerawerk Niedersedlitz Dresden presented the Praktiflex at the Leipzig spring fair. The camera was a waist type with an M40x1 screw mount and a horizontal cloth focal shutter. This camera is the pattern for most of the 35 mm SLR cameras and also for the Japanese and the digital SLR cameras today. After the war, Praktiflex was the most manufactured 35 mm SLR in Dresden, especially for the Russians as reparations. KW changed to the M42 screw mount invented at Zeiss for Contax S—later used by Pentax, Yashica and others to become a near universal mount. In 1949, it was redesigned with longer shutter speeds, and the name was changed to Praktica. In 1958, KW Niedersedlitz became a part of the VEB Kamer und Kinowerk (old Zeiss), later VEB Pentacon. Praktica was typically a consumer/amateur camera. Many developments were added. It was produced until 2000.
Highlights:
From 1952 to 1960 the KW factory/VEB Pentacon also produced the Praktina, a system SLR camera for professionals and advanced amateurs with a bayonet mount and focal shutter, but production was closed, partly for political reasons. Praktica was the camera that could be sold outside the DDR and bring foreign currency to the country.
Edixa.
Another German manufacturer, Edixa was a brand of camera manufactured by Wirgin Kamerawerk, based in Wiesbaden, West Germany. This company's product line included 35mm SLR cameras such as the Edixa Reflex, which featured a Steinheil 55mm f/1.9 Quinon lens and an Isco Travegar 50mm f/2.8 lens, the Edixamat Reflex, the Edixa REX TTL, and the Edixa Electronica.
The removable pentaprism could be swapped for a waistlevel viewfinder with a pop up magnifier.
The lens mount was the same screw thread as the Praktica.
Rise of the Japanese SLRs.
The earliest Japanese SLR for roll film was perhaps the Baby Super Flex (or Super Flex Baby), a 127 camera made by Umemoto and distributed by Kikōdō from 1938. This camera had a leaf shutter, but two years later came the Shinkoflex, a 6×6 camera made by Yamashita Shōkai, with a focal-plane shutter and interchangeable lenses. However, Japanese camera makers concentrated on rangefinder and twin-lens reflex cameras (as well as simpler viewfinder cameras), similar to those of the Western makers.
Pentax.
The Asahi Optical Company took a different manufacturing path, inspired by the German SLRs. Its first model, the Asahiflex I, existed in prototype form in 1951 and production in 1952, making it the first Japanese-built 35mm SLR. The Asahiflex IIB of 1954 was the first Japanese SLR with an instant-return mirror. Previously, the mirror would remain up and the viewfinder black until the user released the shutter button. In 1957, the Asahi Pentax became the first Japanese fixed-pentaprism SLR; its success led Asahi to eventually rename itself Pentax. This was the first SLR to use the right-hand single-stroke film advance lever of the Leica M3 of 1954 and Nikon S2 of 1955. Asahi (starting with the Asahi Pentax) and many other camera makers used the M42 lens mount from the Contax S, which came to be called the Pentax screw mount. Pentax is now part of Ricoh.
Miranda.
Orion's (later name-changed to Miranda's) Miranda SLR camera was sold in Japan from August 1955 with the launch of the Miranda T camera. The camera was narrowly the first Japanese-made pentaprism 35mm SLR. It featured a removable pentaprism for eye-level viewing that could be removed for use as a waist-level finder.
Yashica.
The Yashica Company introduced its own SLR in 1959, the "Pentamatic", an advanced, modern 35mm SLR camera with a proprietary bayonet-mount. The Pentamatic featured an automatic stop-down diaphragm (offered only with the Auto Yashinon 50mm/1.8 lens), instant-return mirror, a fixed pentaprism, and a mechanical focal-plane shutter with speeds of 1-1/1000 second, along with additional interchangeable lenses.
Zunow.
The Zunow SLR, which went on sale in 1958 (in Japan only), was the first japanese 35mm SLR camera with an automatic diaphragm, which stopped down to the preselected aperture upon release of the shutter. (Although this invention had been anticipated by the 1948 Gamma Duflex and 1954 Praktina FX-A which could be used with a semi-automatic diaphragm, which stopped down automatically, but had to be opened manually after the exposure.) The automatic diaphragm feature eliminated one downside to viewing with an SLR: the darkening of the viewfinder screen image when the photographer selected a small lens aperture. The Zunow Optical Company also supplied the Miranda Camera Company with lenses for their Miranda T SLR cameras.
General operation of a 35 mm SLR.
A photographer using an SLR would view and focus with the lens diaphragm (aperture) fully open; he then had to adjust the aperture just before taking the picture.
When the shutter release is pressed the mirror flips up against the viewing screen, the diaphragm closes down (if automatic), the shutter opens and closes, the mirror returns to its 45-degree viewing position (on most or all 35 mm SLRs made since 1970) and the automatic diaphragm re-opens to full aperture.
Most but not all SLRs had shutters behind the mirror, next to the film; if the shutter was in or immediately behind the lens it had to be open before the photographer clicked the shutter and then had to close, then open, then close.
Standardization of designs.
In the following 30 years the vast majority of SLRs standardized the layout of the controls. The film was transported from left to right, so the rewind crank was on the left, followed in order by the pentaprism, shutter speed dial, shutter release, and the film advance lever, which in some cameras was ratcheted so that multiple strokes could be used to advance the film. Some cameras, such as Nikon's Nikomat FT cameras (marketed under the brand-name 'Nikkormat' in European countries and elsewhere) and some models of Olympus OM series, deviated from this layout by placing the shutter speed control as a ring around the lens mount.
Miranda Camera Company.
Miranda produced early SLRs in the 1950s which were initially manufactured with external auto-diaphragms, then added a second mount with internal auto-diaphragm. To list some of Miranda's cameras with external diaphragm, there was the Miranda Sensorex line. The internal auto-diaphragm Miranda cameras consisted of the Miranda 'D', the popular Miranda 'F', the 'FV' and the 'G' model, which had a larger than normal reflex mirror thereby eliminating viewfinder image vignetting when the camera was used with long telephoto lenses. Miranda cameras were known in some photographic discussions as 'the poor man's Nikon'.
Periflex.
One unique brand of cameras was the Corfield Periflex made by K. G. Corfield Ltd in England. Three models were produced from 1957, all of which used a retractable periscope inserted into the light path for focussing through the single lens. Pressing the shutter release moved the spring-loaded periscope out of the film path before the focal-plane shutter operated
Minolta.
Minolta's first SLR, the SR-2, was introduced to the export market in the same year (in fact, at the same Philadelphia show as the Canon and Nikon products) but had been on sale in Japan since August 1958. Lenses started with the designation 'Rokkor'. With the introduction of the SRT-101, the lenses added the designation of 'MC' for 'meter-coupled', and then later to 'MD' when the Minolta XD-11 was introduced with full-program mode.
Minolta was taken over in 2003 by Konica, to form 'Konica-Minolta'. Konica-Minolta sold its imaging division to Sony in January 2006.
Nikon F.
Nikon's 'F' model, introduced in April 1959 as the world's first system camera (if the commercially unsuccessful Praktina is not considered), became enormously successful and was the camera design that demonstrated the superiority of the SLR and of the Japanese camera manufacturers. This camera was the first SLR system that was adopted and used seriously by the general population of professional photographers, especially by those photographers covering the Vietnam War, and those news photographers utilizing motor-driven Nikon F's with 250-exposure backs to record the various launches of the space capsules in the Mercury, Gemini, and Apollo space programs, both in the 1960s. After the introduction of the Nikon F, the more expensive rangefinder cameras (those with focal plane shutters) became less attractive.
It was a combination of design elements that made the Nikon F successful. It featured interchangeable prisms and focusing screens; the camera had a depth-of-field preview button; the mirror had lock-up capability; it featured a large bayonet mount and a large lens release button; a single-stroke ratcheted film advance lever; a titanium-foil focal plane shutter; various types of flash synchronization; a rapid rewind lever; and a fully removable back. it was a well-made, extremely durable camera, and adhered closely to the then current, successful design scheme of the Nikon rangefinder cameras.
Instead of the M42 screw mount used by Pentax and other camera manufacturers, Nikon had introduced the three-claw F-mount bayonet lens mount system, which is still current in a modified form today. The focal plane shutter, unlike other SLRs of the period which used a cloth material for the focal plane shutter design (NOTE: with this design, it was possible to burn a hole into the cloth of the shutter during mirror lock-up in bright sunlight) used titanium foil which was rated for 100,000 cycles of releases of the shutter (according to Nikon). The F was also a modular camera, in which various assemblies such as the pentaprisms, the focusing screens, the special 35mm roll film 250 exposure film back and the Speed Magny film backs (two models: one using the Polaroid 100 (now 600) type pack films; and another Speed Magny was designed for 4×5 film accessories, including Polaroid's own 4×5 instant film back). These could be fitted and removed, allowing the camera to adapt to almost any particular task. It was the first 35 mm camera offered with a successful motor drive system.
Unlike most of the other manufacturers involved in 35mm camera production, the Nikon F was released with a full range of lenses from 21 mm to 1000 mm focal length. Nikon was also among the first to introduce what is commonly known today as 'mirror lenses' – lenses with Catadioptric system designs, which allowed the light path to be folded and thus yielded lens designs that were more compact than the standard telephoto designs. Subsequent top-of-the-line Nikon models carried on the F series, which has reached the F6 (although this camera has a fixed pentaprism). With the introduction and continued improvements being made in digital photography, the Nikon F6 is the last of the flagship Nikon F-line film SLRs.
Canon.
In May 1959, the Canonflex SLR was introduced. The camera featured a quick return mirror and an automatic diaphragm, and was introduced with an interchangeable black pentaprism housing. It also featured newly developed 'R' series breech lock mount lenses. This SLR was superseded by the Canonflex RM, a fixed prism SLR which featured a built-in selenium cell meter. Later came the Canonflex R2000, with a top shutter speed of 1/2000 of a second. This model was also superseded by the Canonflex RM.
In 1962, FL series lenses were introduced along with a new camera body, the Canon FX, which had a built-in CdS light meter positioned on the front left side of the camera, a design which appeared much like the Minolta SR-7.
Olympus Pen F.
The Olympus Pen F series was introduced and produced by Olympus of Japan between 1963 and 1966. The System consisted of the original Olympus Pen F, later the behind-the-lens metering Pen FT, 1966–1972; and the non-metered version of the FT, known as the Olympus Pen FV, which was manufactured from 1967 to 1970. The design considerations used were unusual. The camera produced a half-frame 35 mm negative; it used a Porro prism as a design-replacement for the conventional pentaprism thus producing the 'flat top' appearance; and the view through the viewfinder was of 'portrait' orientation' (unlike standard 35mm SLRs which had 'landscape' orientation). These half-frame cameras were also exceptional in that all used a rotary shutter, rather than the traditional horizontally travelling focal-plane shutter commonly used in other SLR camera designs. The camera was produced with various interchangeable lenses. The smaller image format made the Pen F system one of the smallest SLR camera systems ever made. Only the Pentax Auto 110 was smaller, but the Pentax system was of much more limited range in terms of lenses and accessories.
Introduction of light metering.
Professional Photographers of the 1940s and 1950s time-period preferred to use hand-held meters such as the Weston or GE selenium cell light meters, and others which were common during these periods. These hand-held meters did not require any batteries and provided good analog readouts of shutter speeds, apertures, ASA (now referred to as 'ISO') and EV (exposure value). Selenium cells, however, could easily be judged for their light sensitivity by simply looking at the size of the cell's metering surface. A small surface meant it lacked low-light sensitivity. These would prove to be useless for in-camera light metering.
Built-in light metering with SLRs started with clip-on selenium cell meters. One such meter was made for the Nikon F which coupled to the shutter speed dial and the aperture ring. While the selenium cell area was big, the add-on made the camera look clumsy and unattractive. In order for built-in light metering to be successful in SLR cameras, the use of Cadmium Sulfide Cells (CdS) was imperative.
Some early SLRs featured a built-in CdS meter, usually on the front left side of the top plate, as in the Minolta SR-7. Other manufacturers, such as Miranda and Nikon introduced a CdS prism which fitted to their interchangeable prism SLR cameras. Nikon's early Photomic finder utilized a cover in front of the cell which was raised and a reading was taken and the photographer would either turn the coupled shutter speed dial and/or the coupled aperture ring to center a galvanometer-based meter needle shown in the viewfinder. The disadvantage of this early Photomic prism finder was that the meter had no ON/OFF switch so the meter was constantly 'ON', thus draining battery power. A later Photomic housing had an ON/OFF switch on the Pentaprism. CdS light meters proved more sensitive to light and thus metering in available light situations was becoming more prominent and useful. Further advances in CdS sensitivity, however, were needed as CdS cells suffered from a 'memory effect'. That is, if exposed to bright sunlight, the cell would require many minutes to return to normal operation and sensitivity.
Through-the-lens metering.
Through-the-lens metering measures the light that comes through the camera lens, thus eliminating much of the potential for error inherent in separate light meters. It is of particular advantage with long telephoto lenses, macro photography, and photomicrography. The first SLRs with through-the-lens metering were introduced by Japanese manufacturers in the early to mid-1960s.
Nikon F and F2 with interchangeable photomic prisms.
The Nikon F was delivered since 1962 with various pentaprism metering heads. The Photomic series of prisms, which was initially designed with a direct coupled-metering CdS photocell (2 models were produced). The Photomic prism head later evolved to include the Photomic T with TTL in 1965, a behind-the-lens metering prism head which metered an averaging pattern of the focusing screen. The later center-area reading Photomic Tn, concentrated 60% of its sensitivity in the central portion of the focusing screen and the remaining 40% for the outlying screen area. The Photomic FTn was the last of the Photomic finders for the Nikon F.
In 1972, the Nikon F2 was introduced. It had a more streamlined body, a better mirror-locking system, a top shutter speed of 1/2000 of a second and was introduced with its own proprietary, continually improving Photomic meter prism heads. This camera's construction was mechanically superior to the F, with some models using titanium for the top and bottom cover plates, and featured slower shutter speeds via the self-timer mechanism. All Nikon F and F2 Photomic prism heads coupled to the shutter speed dial of the respective camera, and also to the aperture ring via a coupling prong on the diaphragm ring of the lens. This design feature was incorporated into most Auto Nikkor lenses of that time. Nikon technicians can still install a coupling prong on D type Auto Nikkor lenses so that these newer lenses will fully couple and operate with the older Nikon camera bodies. This is not possible with the G type Auto Nikkor lenses and lenses with the DX designation.
Pentax – the Spotmatic.
Pentax was the first manufacturer to show a prototype camera with a behind-the-lens spot metering CdS meter system in 1961, the Pentax Spotmatic. Production Spotmatics, however, didn't appear until mid-to-late 1964, and these models were featured with an averaging meter system.
Topcon – the RE Super.
Tokyo Optical's Topcon RE Super (Beseler Topcon Super D in the US), however, preceded Pentax into production in 1963. Topcon cameras used behind-the-lens CdS (Cadmium Sulfide Cells) light meters which were integrated into a partially silvered area of the mirror.
Minolta – the SRT-101 with contrast light compensation.
Japanese-made SLRs from the mid-1960s (1966) included the Minolta SRT-101, and later the SRT-202 and 303 models, which used Minolta's own version of behind-the-lens metering which they referred to as CLC (contrast light compensation).
Miranda and other camera manufacturers.
Other camera manufacturers followed with their own behind-the-lens meter camera designs in order to compete in the marketplace. 35mm SLR film cameras such as Miranda with their Miranda Sensomat, unlike most other systems used a behind-the-lens meter system built into the pentaprism itself. Other Miranda 35mm SLR cameras could be adapted to behind-the-lens capability through the use of a separate pentaprism which included coupled or non-coupled built-in CdS meters. Miranda had a second lens system, consisting of the Sensorex models which had an externally coupled auto diaphragm. Sensorex camera bodies had built-in meters and these evolved to include TTL and 'EE' capability.
The 1970s – improvements in design, light metering and automation.
Design.
One of the most significant designs of the seventies for the 35mm SLR camera industry was the introduction of the Olympus OM-1 in 1973. After experiencing success with their small Olympus Pen half-frame cameras, particularly with their half-frame SLR-based Olympus Pen-F, Pen-Ft and Pen-FV cameras, Olympus set out with its chief designer Yoshihisa Maitani to later create a compact SLR—the M-1—with new compact lenses and a large bayonet mount that could accept almost any SLR design optic. Shortly after being launched the camera was renamed the OM-1 to avoid a trademark conflict with Leica. The mechanical, manual OM-1 was significantly smaller and lighter than contemporary SLRs, but no less functional. The camera was supported by one of the most comprehensive 35 mm SLR lens and accessory systems available. Maitani decreased the size and weight by totally redesigning the SLR from the ground up with unprecedented use of metallurgy, which included repositioning the shutter speed selector to the front of the lens mount, instead of a more conventional position on top of the body.
'Off-the-film' electronic flash metering.
Olympus – the OM-2.
Olympus made another significant advance with the OM-2 in 1975, featuring aperture-priority automatic exposure with the world's first off-the-film plane available-light metering and off-the-film (which Olympus referred to as 'OTF') flash metering systems. 
By metering light in real time off the film plane the OM-2 was able to adjust exposure if light levels changed during exposure. By eliminating flash metering via a built-in photocell on a flash unit the OTF system was able to meter more accurately, and also significantly simplify multi-flash shooting as it was no longer necessary to calculate and factor-in exposure for multiple light sources. This system was especially valuable in photomacrography (macrophotography) and photomicrography (microphotography).
The Olympus OM System was further enlarged; its Zuiko lenses gained a reputation as being among the sharpest lenses in the world, and in the 1980's, Olympus added further improvements by replacing the OM-1 and OM-2 cameras with the OM-3, a mechanical manual SLR and the OM-4 automatic, both of which featured multi-spot metering capabilities. These cameras were further improved into the last of the OM SLRs, the titanium-bodied OM-3Ti and OM-4Ti, introducing at the same time, the world's fastest electronic flash synchronization speeds, at 1/2000 second with their new Full-Synchro strobe-based flash technology.
Gradually, other manufacturers incorporated this feature into their own SLR camera designs.
Programmed autoexposure.
By 1974, the autoexposure SLR brands had aligned into two camps (shutter-priority: Canon, Konica, Miranda, Petri, Ricoh and Topcon; aperture-priority: Asahi Pentax, Chinon, Cosina, Fujica, Minolta, Nikkormat and Yashica) supposedly based on the superiority of their chosen mode. (In reality, based on the limitations of the electronics of the time and the ease of adapting each brand's older mechanical designs to automation.) These AE SLRs were only semi-automatic. With shutter-priority control, the camera would set the lens aperture after the photographer chose a shutter speed to freeze or blur motion. With aperture-priority control, the camera would set the shutter speed after the photographer chose a lens aperture f-stop to control depth of field (focus).
Canon – the A-1.
Perhaps the most significant milestone of the 1970s era of SLR computerization was the 1978 release of the Canon A-1, the first SLR with a "programmed" autoexposure mode. Although the Minolta XD11 was the first SLR to offer both aperture-priority and shutter-priority modes in 1977, it was not until the next year that the A-1 came out with a microprocessor computer powerful enough to offer both of those modes and add the ability to automatically set both the shutter speed and lens aperture in a compromise exposure from light meter input.
Programmed autoexposure, in many variations, became a standard camera feature by the mid-1980s. This is the order of first introduction of 35 mm SLRs, by brand, with a computer programmed autoexposure mode, before the rise of autofocus (see next section): 1978, Canon A-1 (plus AE-1 Program, 1981 and T50, 1983); 1980, Fujica AX-5; 1980, Leica R4; 1981, Mamiya ZE-X; 1982, Konica FP-1; 1982, Minolta X-700; 1982, Nikon FG (plus FA, 1983); 1983, Pentax Super Program (plus Program Plus, 1984 and A3000, 1985); 1983, Chinon CP-5 Twin Program (also first with two program modes); 1984, Ricoh XR-P (tied with Canon T70 as first with three program modes); 1985, Olympus OM-2S Program; 1985, Contax 159MM; 1985, Yashica FX-103. Of the brands active in the mid-1970s, Cosina, Miranda, Petri, Praktica, Rolleiflex, Topcon and Zenit never introduced programmed 35 mm SLRs; usually the inability to make the transition forced the company to quit the 35 mm SLR business altogether. Note that the Asahi Pentax Auto 110, Pentax Auto 110 Super (Pocket Instamatic 110 SLRs from 1978 and 1982) and Pentax 645 (a 645 format SLR from 1985) also had programmed autoexposure.
Autofocus revolution.
Autofocus compact cameras had been introduced in the late 1970s. The SLR market of the time was crowded, and autofocus seemed an excellent option to attract novice photographers.
The first autofocus SLR was the 1978 Polaroid SX-70 SONAR OneStep. It used an ultrasonic autofocus system called SONAR.
The first 35 mm SLR (the SX-70 was not 35 mm) with autofocus capability was the Pentax ME F of 1981 (using a special autofocus lens with an integral motor).
In 1981 Canon introduced a self-contained autofocus lens, the 35–70 mm AF, which contained an optical triangulation system that would focus the lens on the subject in the exact center when a button on the side of the lens was pushed. It would work on any Canon FD camera body. Nikon's F3AF was a highly specialized autofocus camera. It was a variant of the Nikon F3 that worked with the full range of Nikon manual focus lenses, but also featured two dedicated AF lenses (an 80 mm and a 200 mm) that coupled with a special AF viewfinder. F3AF lenses were only supported by the F3AF, the F501, and the F4. Nikon's later AF cameras and lenses used an entirely different design.
These cameras, and other experiments in autofocus from other manufacturers, had limited success.
Minolta – the Maxxum 7000.
The first true 35mm SLR autofocus camera that had a successful design was the Minolta Dynax/Maxxum 7000, introduced in 1985. This SLR featured a built-in motor drive and dedicated flash capability. Minolta also introduced a completely new bayonet mount lens system, the Maxxum AF lens system (currently known as the Sony A-Mount), which was incompatible with its previous MD-bayonet mount system, in which the lenses' focusing action was driven from a motor in the camera body. This reduced complexity in the camera body and the lens. Canon responded with the T80 and a range of three motor-equipped "AC" lenses, but this was regarded as a stopgap move. Nikon introduced the N2020 (known in Europe as the Nikon F-501), which was their first SLR with built-in autofocus motor, and redesigned autofocus Auto Nikkor lenses. Nikon's AF lenses, however, remained compatible with older Nikon 35mm SLR cameras, and older manual focus Nikon lenses could be used with varying degrees of compatibility on the new AF cameras.
Canon – the new EOS System.
In 1987, Canon followed Minolta in introducing a new lens-mount system, which was incompatible with their previous mount-system: EOS, the "Electro-Optical System". Unlike Minolta's motor-in-body approach, this design located the motor within the lens. New, more compact motor designs meant that both focus and aperture could be driven electrically without motor bulges in the lens. The Canon EF lens mount has no mechanical linkages; all communication between body and lens is electronic.
Nikon and Pentax.
Nikon and Pentax both chose to extend their existing lens mounts with autofocus capability, retaining the ability to use older manual-focus lenses with an autofocus body, and driving the lens focus mechanism with a motor inside the camera. Later, Nikon added Silent Wave Motor (SWM) mechanisms into its lenses, supporting both focusing schemes until the introductions of the entry-level Nikon D40 and Nikon D40X in 2006. Pentax introduced its Supersonic Drive Motor (SDM) in 2006 with Pentax K10D model and two lenses (DA*16-50/2.8 AL ED [IF] SDM and DA*50-135/2.8 ED [IF] SDM). Since then all Pentax DSLR support both SDM and the motor inside the body. Earlier SDM lenses support both systems as well. The first SDM lens that did not support the old focusing system was the DA 17-70/4 AL [IF] SDM (2008).
Consolidation to autofocus and the transition to digital photography.
The major 35mm camera manufacturers, Canon, Minolta, Nikon, and Pentax were among the few companies to transition successfully to autofocus. Other camera manufacturers also introduced functionally successful autofocus SLRs but these cameras were not as successful. Some manufacturers eventually withdrew from the SLR market.
Nikon still markets its manual-focus SLR, the FM10. Olympus continued production of its OM system camera line until 2002. Pentax also continued to produce the manual-focus LX until 2001. Sigma and Fujifilm also managed to continue manufacturing cameras, although Kyocera ended production in 2005 of its (Contax) camera systems. The newly formed Konica Minolta sold its camera business to Sony two years later.
Arrival of digital photography.
In the 2000s, film became supplanted by digital photography, which had a huge impact on all camera manufacturers, including the SLR market. Nikon, for instance, has ceased production of all film SLRs except for its flagship 35 mm SLR film camera, the F6; and the introductory-level Nikon FM10.
Replacing film with a similar-sized digital sensor is possible, but expensive because larger sensor areas imply a greater probability that a defect will render the sensor non-functional. Such "full frame" sensor digital SLRs (DSLRs) however gained early popularity with professional photographers who could both justify their initial high cost, and retain the use of their investment in expensive 35 mm film lenses. By 2008, full-frame models such the Canon EOS 1Ds and 5D, the Nikon D3 and D700, and the Sony Alpha A850 and Alpha A900, designed and priced for professionals, were available.
As of 2017, several manufacturers have introduced more affordable 35 mm sensor SLRs such as the Canon EOS 6D, the Nikon D610 and the new Pentax K-1. These cameras, while still positioned as premium products, all retail for less than 3000$; significantly, all but the K-1 are priced below the manufacturer's top APS-C camera. In addition, the full-frame format is now found in Sony's MILC cameras and high-end fixed prime lens compacts, as well as Leica's M-mount digital rangefinders.
SLRs designed for amateurs and consumers generally use APS-C sensors, which are significantly smaller than 35 mm film frames and these require either their own specialist lenses or accepting a change in equivalent focal length and field-of-view angle when using lenses designed for the 35 mm format (wide-angle lenses become normal, normal become short telephoto, etc.).
During most of the 2000s, Panasonic and Olympus also marketed SLRs built around the now-defunct Four-Thirds System, which was even smaller.
Medium-format SLRs.
While twin-lens reflex cameras have been more numerous in the medium format film category, many medium-format SLRs had been (and some still are) produced. Hasselblad of Sweden has one of the best-known camera systems utilizing 120 and 220 film to produce 6 cm × 6 cm (2" × 2") negatives. They also produce other film backs which produce a 6 cm × 4.5 cm image; a back which uses 70mm roll film, a Polaroid Back for instant 'proofs' and even a 35mm film back.
Pentax produces two medium-format SLR systems, the Pentax 645, which produces a 6 cm × 4.5 cm image; and the Pentax 67 series, which system evolved from the late 1960s introduced Pentax 6 × 7 camera. These Pentax 6 × 7 series cameras resembled huge 35mm SLR camera in look and function.
In 2010 Pentax introduced a digital version of the 645, the 645D, with a Kodak-built 44X33 sensor.
Bronica (which has discontinued camera production), Fuji, Kyocera (which has also ceased production of their Contax cameras), Mamiya, Rollei, Pentacon (former East Germany), and Kiev (former Soviet Union) have also produced Medium Format SLR systems for a considerable period of time. Mamiya produces what is termed a medium format digital SLR. Other medium-format SLRs, such as those from Hasselblad, accept digital backs in place of film rolls or cartridges, effectively converting their film designs to digital format use.
In the case of Polaroid Corporation with its instant film line, the introduction of the Polaroid SX-70 was one of the few SLRs produced that was a rare case of a folding SLR.
Future.
The vast majority of SLRs now sold are digital models, even though their size, form factor, and other design elements remain derived from their 35 mm film predecessors. Whether a dedicated digital design such as the Olympus Four-Thirds system, which permits equivalent performance with smaller and lighter cameras, will ultimately supersede the film-derived designs from Canon, Nikon, Pentax, and Sony is as yet unclear. Additionally SLRs are facing a threat from the rapidly expanding mirrorless interchangeable-lens camera segment among all types of camera user.
Chronology.
Significant SLR technology firsts (including optics peculiar to SLRs and important SLR evolutionary lines now extinct).
1930s.
The Sport (camera) is the series production model of a prototype camera called Gelveta. The Gelveta was designed and built by A. O. Gelgar between 1934 and 1935. It is the earliest known 35mm SLR camera ever to be built, but fewer than 200 examples were made. It was manufactured by the Soviet camera factory Gosudarstvennyi Optiko-Mekhanicheskii Zavod, The State Optical-Mechanical Factory in Leningrad. GOMZ for short. The camera name is engraved in Cyrillic on the finder housing above the lens: „Спорт“. The manufacturer's prism logo in gold on black with the factory initials ГОМЗ (GOMZ) is shown behind a circular magnifying window on the top left camera front. An estimated number of 16,000 cameras were made