Single-lens reflex camera

A single-lens reflex camera (SLR) is a camera that

typically uses a mirror and prism system (hence
"reflex" from the mirror's reflection) that permits the
photographer to view through the lens and see exactly
what will be captured. With twin lens reflex and
rangefinder cameras, the viewed image could be
significantly different from the final image. When the

Ihagee Exa Single lens reflex

The Zeiss Ikon VEB Contax S,

manufactured in Dresden, one of the two
original pentaprism SLRs for eye-level
viewing that went into production in 1949.
The Italian Rectaflex offered its first
production SLR, the series 1000, the
same year.
shutter button is pressed on most SLRs, the mirror flips out of the light path, allowing light to pass through
to the light receptor and the image to be captured.

History

Medium format SLR Medium format SLR The 1952 (Pentax) The Contaflex III a
by Hasselblad by Bronica (Model Asahiflex, Japan's single-lens reflex
(Model 1600F), S2), Japan. first single-lens camera from West
Sweden Bronica's later reflex camera. Germany from 1957,
model—the Bronica with additional
EC—was the first 115 mm lens
medium format SLR
camera to use an
electrically operated
focal-plane shutter

The 35 mm film- Canon Pellix, 1965, The Pentax Olympus The 35 mm

based Nikon F, the first camera to Spotmatic IIa, 1971 film-based Olympus
1959, the world's incorporate a OM-2 (1975), which
second single-lens stationary pellicle was the first SLR to
reflex system mirror. measure light for
camera. The first electronic flash off
was Kamera- the film plane.
Werke's Praktina.
 Casio RF2 35 mm Nikon F5 Digital SLR Nikon Zenit, a Russian
film SLR professional SLR, D200 and a Nikon brand. SLR without
1996 film scanner lens kit

Until the development of SLR, all cameras with viewfinders had

two optical light paths: one through the lens to the film, and another
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, it is not easy to focus the lens of a fast reflex camera
Cross section of SLR camera.
when it is opened to wider apertures (such as in low light or while
using low-speed film).

Most SLR cameras permit upright and laterally correct viewing through use of a roof pentaprism situated in
the optical path between the reflex mirror and viewfinder. Light, which comes both horizontally and
vertically inverted after passing through the lens, is reflected upwards by the reflex mirror, into the
pentaprism where it is reflected several times to correct the inversions caused by the lens, and align the
image 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). Exceptions to
the moving mirror system include the Canon Pellix and Sony SLT cameras, along with several special-
purpose high-speed cameras (such as the Canon EOS-1N RS), whose mirror was a fixed beamsplitting
pellicle.

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.

Large format SLR cameras were probably first marketed with the introduction of C.R. Smith's Monocular
Duplex (U.S., 1884).[1] 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
200 mm f4.5 lens paired to a 35 mm rangefinder camera body, debuted in 1935. The Soviet Спорт
(“Sport”),[2] also a 24 mm by 36 mm image size, was prototyped in 1934 and went to market in 1937. K.
Nüchterlein's Kine Exakta (Germany, 1936) was the first integrated 35 mm SLR to enter the market.
Additional Exakta 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 Italian Rectaflex A.1000,
shown in full working condition on Milan fair April 1948 and produced from September the same year,
thus being on the market one year before the east German Zeiss Ikon VEB Contax S, announced on May
20, 1949, produced from September.

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).

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 website below, the
camera used Nikon 'S' type rangefinder lenses.[3]

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 Spotmatic. 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.

Semi-automatic exposure capabilities

While auto-exposure was commonly used in the early 1960s with various 35 mm fixed lens rangefinder
cameras such as the Konica Auto 'S', and other cameras such as the Polaroid Land cameras whose early
models used selenium cell meters, auto-exposure for interchangeable lens SLRs was a feature that was
largely absent, except for a few early leaf-shutter SLRs such as the Kowa SE-R and Topcon Auto 100.

The types of automation found in some of these cameras consisted of the simple programmed shutter,
whereby the camera's metering system would select a mechanically set series of apertures with shutter
speeds, one setting of which would be sufficient for the correct exposure. In the case of the above-
mentioned Kowa and Topcon, automation was semi-automatic, where the camera's CDs meter would select
the correct aperture only.

Autoexposure, technically known as semi-automatic exposure, where the camera's metering system
chooses either the shutter speed or the aperture, was finally introduced by the Savoyflex and popularized by
Konishiroku in the 1965 Konica Auto-Reflex. This camera was of the 'shutter-priority' type automation,
which meant that the camera selected the correct aperture automatically. This model also had the interesting
ability to photograph in 35 mm full-frames or half-frames, all selected by a lever.

Other SLRs soon followed, but because of limitations with their lens mounts, the manufacturers of these
cameras had to choose 'aperture-priority' automation, where the camera's metering system selects the correct
shutter speed. As one example, Pentax introduced the Electro Spotmatic, which was able to use the then
considerable bulk of 42 mm screw-mount lenses produced by various manufacturers. Yashica, another
screw-mount camera manufacturer, soon followed.

Canon, which produced the FD lens mount (known as the breech-mount; a unique lens mounting system
that combines the advantages of screw-mount and bayonet-mount) introduced their shutter priority 35 mm
SLR, the Canon EF in 1976 or so. This camera's build quality was almost the equal of their flagship
camera, the Canon F1, and featured a copal-square vertically travelling focal plane shutter that could
synchronize electronic flash at shutter speeds up to and including 1/125 of a second, thus making this a
good second-body camera for the professional photographer.

Nikon at first produced an aperture-priority camera, but later made subtle changes on the inside of their
bayonet mount, which allowed for shutter-priority automation without obsoleting the photographers lenses.

Full-program auto-exposure

Full-program auto-exposure soon followed with the Minolta XD-11 (also XD-7 and XD)
advent of the Canon A-1 in 1978. This SLR had a 'P'
mode on the shutter speed dial, and a lock on the
aperture ring to allow the lens to be put on 'Auto'
mode. Other manufacturers soon followed with Nikon
introducing the FA, Minolta introducing the X-700 in
1981,[4] and Pentax introducing the Super Program.
Olympus, however, continued with 'aperture-priority'
automation in their OM system line.

The 1970s and 1980s saw steadily increasing use of

electronics, automation, and miniaturization, including
integrated motor driven film advance with the Konica
FS-1 in 1979,[5] and motor rewind functions. Overview
Type 35 mm SLR
Autofocus Lens
Lens Minolta SR-mount
The first autofocus 35 mm SLR was the Pentax ME-F
mount
released in 1981.[6]
Focusing
The Minolta Maxxum 7000, released in 1985, was the Focus Manual focus SLR
first 35 mm SLR with integrated autofocus and
motorized film-advance winder, which became the Exposure/metering
standard configuration for SLR cameras from then on. Exposure Shutter and aperture priority
This development had significant impact on the autoexposure
photographic industry.
Flash
Some manufacturers discarded their existing lens Flash Hot shoe only; no PC connector
systems to compete with other manufacturer's
General
autofocus capability in their new cameras. This was the
case for Canon, with its new EOS lens line. Other Dimensions 51 × 86 × 136 mm, 560 g
manufacturers chose to adapt their existing lens systems
for autofocus capability, as was the case with Nikon and Pentax. This allowed photographers to continue
using their existing lenses, which greatly reduced the cost of upgrading. For example, almost all Nikon
lenses from the 1960s and later still function on the current Nikon bodies, only lacking autofocus. Still
some manufacturers, notably Leica with its R-system lenses, and Contax with its Zeiss lenses, decided to
keep their lens mounts non-autofocus.

From the late 1980s competition and technical innovations made 35 mm camera systems more versatile and
sophisticated by adding more advanced light metering capabilities such as spot-metering; limited area
metering such as used by Canon with the F1 series; matrix metering as used by Nikon, exposure
communication with dedicated electronic flash units. The user interface also changed on many cameras,
replacing meter needle displays that were galvanometer-based and
thereby fragile, with light-emitting diodes (LEDs) and then with
more comprehensive liquid crystal displays (LCDs) both in the
SLR viewfinder and externally on the cameras' top plate using an
LCD screen. Wheels and buttons replaced the shutter dial on the
camera and the aperture ring on the lens on many models, although
some photographers still prefer shutter dials and aperture rings.
Some manufacturers introduced image stabilization on certain
lenses to combat camera shake and to allow longer hand-held
exposures without using a tripod. This feature is especially useful Typical film SLR viewfinder
with long telephoto lenses. information

Digital SLRs

Canon, Nikon and Pentax have all developed digital SLR cameras (DSLRs) using the same lens mounts as
on their respective film SLR cameras.[7] Konica Minolta did the same, and after having bought Konica
Minolta's camera division in 2006 Sony continue using the Minolta AF lens mount in their DSLRs,
including cameras built around a semi-transparent fixed mirror. Samsung builds DSLRs based on the
Pentax lens mount. Olympus, on the other hand, chose to create a new digital-only Four Thirds System
SLR standard, adopted later by Panasonic and Leica.

Contax came out with a DSLR model, the Contax N-Digital. This model was too late and too expensive to
be competitive with other camera manufacturers. The Contax N-digital was the last Contax to use that
maker's lens system, and the camera, while having impressive features such as a full-frame sensor, was
expensive and lacked sufficient write-speed to the memory card for it to be seriously considered by some
professional photographers.

The digital single-lens reflex camera have largely replaced film SLRs design in convenience, sales and
popularity at the start of the 21st century.

Optical components
A cross-section (or 'side-view') of the optical components of a
typical SLR camera shows how the light passes through the
lens assembly (1), is reflected by the mirror (2) placed at a 45-
degree angle, and is projected on the matte focusing screen (5).
Via a condensing lens (6) and internal reflections in the roof
pentaprism (7) the image appears in the eyepiece (8). When an
image is taken, the mirror moves upwards from its resting
position in the direction of the arrow, the focal plane shutter (3)
opens, and the image is projected onto the film or sensor (4) in
exactly the same manner as on the focusing screen. Focusing screen on Praktica Super
TL1000
This feature distinguishes SLRs from other cameras as the
photographer sees the image composed exactly as it will be
captured on the film or sensor (see Advantages below).

Pentaprisms and penta-mirrors

Most 35 mm SLRs use a roof pentaprism or penta-mirror to
direct the light to the eyepiece, first used on the 1948 Duflex[8]
constructed by Jenő Dulovits and patented August 1943
(Hungary). With this camera also appeared the first Instant-
return mirror. The first Japanese pentaprism SLR was the 1955
Miranda T, followed by the Asahi Pentax, Minolta SR-2,
Zunow, Nikon F and the Yashica Pentamatic. Some SLRs
offered removable pentaprisms with optional viewfinder
capabilities, such as the waist-level finder, the interchangeable
sports finders used on the Canon F1 and F1n; the Nikon F, F2,
F3, F4 and F5; and the Pentax LX.
Cross-section view of SLR system: 1:
Another prism design was the porro prism system used in the
Front-mount lens (four-element Tessar
Olympus Pen F, the Pen FT, the Pen FV half-frame 35 mm
design) 2: Reflex mirror at 45-degree
SLR cameras. This was later used on the Olympus EVOLT E-
angle 3: Focal plane shutter 4: Film or
3x0 series, the Leica Digilux 3 and the Panasonic DMC-L1.
sensor 5: Focusing screen 6: Condenser
lens 7: Optical glass pentaprism (or
A right-angle finder is available that slips onto the eyepiece of
pentamirror) 8: Eyepiece (can have
most SLRs and D-SLRs and allows viewing through a waist-
diopter correction ability)
level viewfinder. There is also a finder that provides EVF
remote capability.

Shutter mechanisms

Focal-plane shutters

Almost all contemporary SLRs use a focal-plane shutter

located in front of the film plane, which prevents the light from
reaching the film even if the lens is removed, except when the
shutter is actually released during the exposure. There are
various designs for focal plane shutters. Early focal-plane
A perspective drawing showing how a roof
shutters designed from the 1930s onwards usually consisted of
pentaprism corrects a laterally reversed
two curtains that travelled horizontally across the film gate: an SLR image.
opening shutter curtain followed by a closing shutter curtain.
During fast shutter speeds, the focal-plane shutter would form
a 'slit' whereby the second shutter curtain was closely following the first opening shutter curtain to produce
a narrow, vertical opening, with the shutter slit moving horizontally. The slit would get narrower as shutter
speeds were increased. Initially these shutters were made from a cloth material (which was in later years
often rubberised), but some manufacturers used other materials instead. Nippon Kōgaku (now Nikon
Corporation), for example, used titanium foil shutters for several of their flagship SLR cameras, including
the Nikon F, F2, and F3.

Other focal-plane shutter designs, such as the Copal Square, travelled vertically — the shorter travelling
distance of 24 millimetres (as opposed to 36 mm horizontally) meant that minimum exposure and flash
synchronisation times could be reduced. These shutters are usually manufactured from metal, and use the
same moving-slit principle as horizontally travelling shutters. They differ, though, in usually being formed
of several slats or blades, rather than single curtains as with horizontal designs, as there is rarely enough
room above and below the frame for a one-piece shutter. Vertical shutters became very common in the
1980s (though Konica, Mamiya, and Copal first pioneered their use in the 1950s and 1960s, and are almost
exclusively used for new cameras. Nikon used Copal-made vertical plane shutters in their
Nikomat/Nikkormat -range, enabling x-sync speeds from 1 ⁄30 to 1 ⁄125 while the only choice for focal plane
shutters at that time was 1 ⁄60 . Later, Nikon again pioneered the use of titanium for vertical shutters, using a
special honeycomb pattern on the blades to reduce their weight and achieve world-record speeds in 1982 of
1⁄ 1
4000 second for non-sync shooting, and ⁄250 with x-sync. Nowadays most such shutters are
manufactured from cheaper aluminium (though some high-end cameras use materials such as carbon-fibre
and Kevlar).

Rotary focal-plane shutter

One unusual design, the Olympus Pen half-frame 35 mm SLR system, manufactured by Olympus in Japan,
used a rotary focal-plane shutter mechanism that was extremely simple and elegant in design. This shutter
used titanium foil but consisted of one piece of metal with a fixed opening, which allowed electronic flash
synchronisation up to and including its maximum speed of 1/500 of a second – rivalling the capabilities of
leaf-shutter systems

Another 35 mm camera system that used a rotary shutter, was the Robot Royal cameras, most of which
were rangefinder 35 mm cameras. Some of these cameras were full-frame; some were half-frame, and at
least one Robot camera produced an unusual square-sized image on the 35 mm frame.

The Mercury II, produced in 1946, also used a rotary shutter. This was a half-frame 35 mm camera.

Leaf shutters

Another shutter system is the leaf shutter, whereby the shutter is constructed of diaphragm-like blades and
can be situated either between the lens or behind the lens. If the shutter is part of a lens assembly some
other mechanism is required to ensure that no light reaches the film between exposures.

An example of a behind-the-lens leaf shutter is found in the 35 mm SLRs produced by Kodak, with their
Retina Reflex camera line; Topcon, with their Auto 100; and Kowa with their SE-R and SET-R reflexes.

A primary example of a medium-format SLR with a between-the-lens leaf shutter system would be
Hasselblad, with their 500C, 500 cm, 500 EL-M (a motorized Hasselblad) and other models (producing a
6 cm square negative). Hasselblads use an auxiliary shutter blind situated behind the lens mount and the
mirror system to prevent the fogging of film.

Other medium-format SLRs also using leaf shutters include the now discontinued Zenza-Bronica camera
system lines such as the Bronica ETRs, the ETRs'i (both producing a 6 × 4.5 cm. image), the SQ and the
SQ-AI (producing a 6 × 6 cm image like the Hasselblad), and the Zenza-Bronica G system (6 × 7 cm).
Certain Mamiya medium-format SLRs, discontinued camera systems such as the Kowa 6 and a few other
camera models also used between-the-lens leaf shutters in their lens systems.

Thus, any time a photographer purchased one of these lenses, that lens included a leaf shutter in its lens
mount.

Because leaf shutters synchronized electronic flash at all shutter speeds especially at fast shutter speeds of
1⁄
500 of a second or faster, cameras using leaf shutters were more desirable to studio photographers who
used sophisticated studio electronic flash systems.
Some manufacturers of medium-format 120 film SLR cameras also made leaf-shutter lenses for their focal-
plane-shutter models. Rollei made at least two such lenses for their Rolleiflex SL-66 medium format which
was a focal-plane shutter SLR. Rollei later switched to a camera system of leaf-shutter design (e.g., the
6006 and 6008 reflexes) and their current medium-format SLRs are now all of the between-the-lens shutter
design.

Further developments
Since the technology became widespread in the 1970s,
SLRs have become the main photographic instrument
used by dedicated amateur photographers and
professionals. Some photographers of static subjects
(such as architecture, landscape, and some commercial
subjects), however, prefer view cameras because of the
capability to control perspective.[9] With a triple-
extension bellows 4" × 5" camera such as the Linhof
SuperTechnika V, the photographer can correct certain
distortions such as "keystoning", where the image
'lines' converge (i.e., photographing a building by
pointing a typical camera upward to include the top of
the building). Perspective correction lenses are
available in the 35 mm and medium formats to correct Parts
this distortion with film cameras, and it can also be
corrected after the fact with photo software when using
digital cameras. The photographer can also extend the bellows to its full length, tilt the front standard and
perform photomacrography (commonly known as 'macro photography'), producing a sharp image with
depth-of-field without stopping down the lens diaphragm.

Film formats
Early SLRs were built for large format photography, but this film format has largely lost favor among
professional photographers. SLR film-based cameras have been produced for most film formats as well as
for digital formats. These film-based SLRs use the 35 mm format as, this film format offers a variety of
emulsions and film sensitivity speeds, usable image quality and a good market cost. 35 mm film comes in a
variety of exposure lengths: 20 exposure, 24 exposure and 36 exposure rolls. Medium format SLRs provide
a higher-quality image with a negative that can be more easily retouched than the smaller 35 mm negative,
when this capability is required.

A small number of SLRs were built for APS such as the Canon IX series and the Nikon Pronea cameras.
SLRs were also introduced for film formats as small as Kodak's 110, such as the Pentax Auto 110, which
had interchangeable lenses.

The Narciss camera is an all-metal 16 mm subminiature single lens reflex camera made by Russian optic
firm Krasnogorsky Mekhanichesky Zavod (KMZ) Narciss (Soviet Union; Нарцисс) between 1961 and
1965.

Common features
Other features found on many SLR cameras include
through-the-lens (TTL) metering and sophisticated
flash control referred to as "dedicated electronic flash".
In a dedicated system, once the dedicated electronic
flash is inserted into the camera's hot shoe and turned
on, there is then communication between camera and
flash. The camera's synchronization speed is set, along
with the aperture. Many camera models measure the
light that reflects off of the film plane, which controls
the flash duration of the electronic flash. This is
denoted TTL flash metering.

Some electronic flash units can send out several short 16 mm SLR Narciss camera
bursts of light to aid the autofocus system or for
wireless communication with off-camera flash units. A
pre-flash is often used to determine the amount of light that is
reflected from the subject, which sets the duration of the main flash
at time of exposure. Some cameras also employ automatic fill-flash,
where the flash light and the available light are balanced. While
these capabilities are not unique to the SLR, manufacturers included
them early on in the top models, whereas the best rangefinder
cameras adopted such features later.

Advantages Cut-away of a Minolta XE film-based

SLR
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.

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
During an exposure, the viewfinder is
image. To avoid the noise and vibration, many professional cameras blocked
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. More recently, Sony have resurrected the pellicle mirror concept in their "single-lens
translucent" (SLT) range of cameras.

Reliability

SLRs vary widely in their construction and typically have bodies made of plastic or magnesium. Most
manufacturers do not 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 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.

Price and affordability

The price of SLRs in general also tends to be somewhat higher than that of other types of cameras, owing
to their internal complexity. This is compounded by the expense of additional components, such as flashes
or lenses. The initial investment in equipment can be prohibitive enough to keep some casual photographers
away from SLRs, although the market for used SLRs has become larger particularly as photographers
migrate to digital systems.

Future
The digital single-lens reflex camera has largely replaced the film SLR for its convenience, sales, and
popularity at the start of the 21st century. These cameras were the marketing favorite among advanced
amateur and professional photographers through the first two decades of the 2000s. Around 2020, the
mirrorless technology utilized in point and shoot cameras made the way to the interchangeable lens cameras
and quickly replaced DSLR technology.

As of 2022, all the major camera brands ceased development and production of DSLRs and moved on to
mirrorless systems. These systems offer multiple advantages to the photographer with regards to autofocus
systems as well as the ability to update the lens technologies due to the reduced distance between the back
of the lens and the sensor resulting from the removal of the mirror.

Film-based SLRs are still used by a niche market of enthusiasts and format lovers.[10]

See also
Asahi Pentax
Fujifilm
Lenses for SLR and DSLR cameras
Scheimpflug principle
Zeiss Ikon

References
1. One was patented in 1861 (Thomas Sutton), but it is not clear if a second example was ever
produced; Calvin Rae Smith's design of a Patent Monocular Duplex camera was advertised
and sold. Spira, The History of Photography, 119.
2. A. O. Gelgar's Sport
3. Stephen, Gandy. "Nikon Shibata Book" (http://www.cameraquest.com/nrfstory.htm). Stephen
Gandy's CameraQuest. Retrieved 2008-06-08.
4. "The Rokkor Files the minolta x-700" (http://www.rokkorfiles.com/X-700.html). The Rokkor
Files. November 23, 2010. Retrieved 2010-11-23.
5. "Those smart new 35 mm automatic cameras". Changing Times. 34.005:23: 23–26. 1980 –
via Proquest.
6. Pentax Imaging Company. "History of Innovations 1980–1989" (https://web.archive.org/web/
20070928041715/http://www.pentaximaging.com/world_of_pentax/history_of_innovations/1
980-1989/index.jsp). Pentax history of innovations. Archived from the original (http://www.pe
ntaximaging.com/world_of_pentax/history_of_innovations/1980-1989/index.jsp) on 2007-09-
28. Retrieved 2006-10-22.
7. Busch, David D. (2014-09-15). Digital SLR Cameras and Photography For Dummies (https://
books.google.com/books?id=rixBBAAAQBAJ&q=Canon%2C+Nikon+and+Pentax+have+all
+developed+digital+SLR+cameras+%28DSLRs%29+using+the+same+lens+mounts+as+o
 n+their+respective+film+SLR+cameras.&pg=PA109). John Wiley & Sons. ISBN 978-1-118-
97183-3.
8. "Article at Photopedia" (http://bichkov.com/photopedia/index.php?title=SLR_Camera).
Bichkov.com. 2008-01-23. Retrieved 2013-10-15.
9. Tal, Guy. "Introduction to Large Format" (http://www.naturephotographers.net/articles0703/gt
0703-1.html). Nature Photographers Online Magazine. Retrieved 2007-08-28.
10. "ARRI, Panavision, and Aaton Cease Production of Film Cameras; Will Focus Exclusively
on Digital" (http://collider.com/film-camera-production-ended-arri-panavision-aaton/).
Collider. 12 October 2011.

Further reading
Spira, S. F. The History of Photography as Seen through the Spira Collection. New York:
Aperture, 2001. ISBN 0-89381-953-0.
Antonetto, Marco: "Rectaflex – The Magic Reflex". Nassa Watch Gallery, 2002. ISBN 88-
87161-01-1

External links
Photography in Malaysia's Contax History, Part II (http://www.mir.com.my/rb/photography/htm
ls/contax_history/history2.htm).
'Innovative Cameras' by Massimo Bertacchi (https://web.archive.org/web/19991008124708/
http://www.geocities.com/RainForest/Andes/3256/innocams.html)
Rolleiflex SL 66 (https://sl66.eu/) (Rolleiflex SL 66 Medium Format Single Lens Reflex
camera).

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