What is · 12 min
What Is an SLR Camera?
An SLR is a camera that uses the same lens for viewing and taking the photograph. A movable mirror redirects light into an optical viewfinder before the exposure.
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What is · 12 min
An SLR is a camera that uses the same lens for viewing and taking the photograph. A movable mirror redirects light into an optical viewfinder before the exposure.
Loading article…
An SLR is a camera that uses the same lens for composing the image and making the exposure. Inside the camera, a movable mirror redirects light from the lens into an optical viewfinder. When the shutter is released, the mirror rises and the light reaches the film.
The initials stand for Single-Lens Reflex. The term describes the viewing system, not the film size, the lens mount or the level of automation.
Most people associate SLR cameras with 35mm film such as the Nikon F3, Canon AE-1 or Pentax K1000. The same principle was also used in medium-format systems including the Hasselblad 500C/M, Mamiya RB67 and Pentax 67.
SLR stands for Single-Lens Reflex.
"Single-lens" means that the camera uses one optical path for both viewing and exposure. It does not mean that the camera has only one permanently attached lens. Many SLRs accept interchangeable lenses.
"Reflex" refers to the internal mirror. During composition, this mirror reflects — or redirects — the image upward toward the focusing screen and viewfinder.
This arrangement allows the photographer to observe the scene through the taking lens. Changes in focus, focal length and depth of field can therefore be viewed directly.
A camera is considered an SLR when it has three defining characteristics:
The recording medium may be photographic film or a digital sensor. A digital camera using the same mirror arrangement is normally called a DSLR, meaning Digital Single-Lens Reflex.
An SLR may be mechanical, electronic, manual-focus or autofocus. It may use a fixed lens or an interchangeable-lens mount. These features do not determine whether the camera is an SLR.
The operation of an SLR can be divided into two phases: viewing and exposure.
Before the shutter is released, light enters through the lens and reaches a mirror positioned at roughly 45 degrees.
The mirror reflects the light upward onto a focusing screen. The image then passes through a pentaprism or pentamirror before reaching the photographer's eye.
The prism corrects the orientation of the image. Without it, the view would appear laterally reversed or inconveniently oriented.
At this stage:
When the shutter button is pressed, the mirror rises out of the optical path.
The focal-plane shutter then opens for the selected exposure time. Light travels directly from the lens to the film, where the image is recorded.
Once the exposure is complete:
The entire cycle may take only a fraction of a second.
Although designs vary, most film SLRs contain the same basic optical and mechanical components.
The lens gathers and focuses light. On an SLR, it is used for both viewing and exposure.
The mirror redirects the image toward the viewfinder while the photographer is composing. It rises immediately before the shutter opens.
The focusing screen is the surface on which the lens forms a visible image. Depending on the camera, it may include a split-image rangefinder, microprism collar, grid or plain matte area.
Some professional SLRs use interchangeable focusing screens for different types of photography.
The pentaprism corrects the orientation of the image and directs it toward the eyepiece.
A pentamirror performs a similar function using mirrors rather than a solid glass prism. Pentamirror systems are generally lighter but may produce a less bright view.
The optical viewfinder allows the photographer to compose and focus without using a screen or electronic display.
Many SLR viewfinders also show exposure information, shutter speed, aperture, focus confirmation or metering indicators.
Most 35mm SLRs use a focal-plane shutter positioned directly in front of the film.
Some medium-format SLR systems use leaf shutters inside their lenses. The Hasselblad 500C/M is a well-known example.
The film is held flat at a precisely defined distance behind the lens mount. Correct alignment is essential for accurate focus.
The viewfinder becomes dark because the mirror must move out of the way before light can reach the film.
While the mirror is raised, it no longer reflects an image toward the focusing screen. The photographer therefore sees a brief blackout during the exposure.
At fast shutter speeds, this interruption may be barely noticeable. During a long exposure, the viewfinder remains dark until the shutter closes and the mirror returns.
Some early SLRs used non-instant-return mirrors. After an exposure, the viewfinder remained dark until the film was advanced or the shutter was recocked. The instant-return mirror later became standard on most SLR cameras.
Not necessarily.
The term SLR describes the optical mechanism. It does not specify the recording medium.
A traditional SLR records the image on photographic film. A DSLR uses a digital sensor but retains the mirror, focusing screen and optical viewfinder arrangement.
In everyday use, however, "SLR" often refers specifically to a film camera, while "DSLR" identifies its digital descendant.
Mirrorless digital cameras are not SLRs because they do not use a reflex mirror.
An SLR and a DSLR use a broadly similar viewing system. The main distinction is how the image is recorded.
| Feature | Film SLR | DSLR |
|---|---|---|
| Recording medium | Photographic film | Digital image sensor |
| Viewing system | Mirror and optical viewfinder | Mirror and optical viewfinder |
| Image review | After film development | Immediately on a screen |
| Storage | Individual film frames | Memory card |
| ISO | Determined mainly by the loaded film | Adjustable electronically |
| Image processing | Film and development process | In-camera or computer processing |
A DSLR is therefore not the opposite of an SLR. It is a digital form of the same basic camera architecture.
A mirrorless camera removes the reflex mirror and optical viewing path.
Instead of looking directly through the lens by means of a mirror and prism, the photographer views an electronic image from the sensor. This image appears on a rear screen or electronic viewfinder.
| Feature | SLR | Mirrorless camera |
|---|---|---|
| Reflex mirror | Yes | No |
| Viewfinder | Optical | Electronic or none |
| Viewfinder blackout | Caused by mirror movement | Depends on sensor readout |
| Body depth | Requires space for mirror | Can be shorter |
| View before exposure | Direct optical image | Electronic preview |
| Battery dependence | Varies by model | Normally essential |
The absence of a mirror allows shorter lens-to-sensor distances and fewer moving parts. An optical SLR viewfinder, however, does not require a live electronic display.
A rangefinder camera uses a separate viewing and focusing system. The photographer does not normally look through the taking lens.
This creates several practical differences.
| Feature | SLR | Rangefinder |
|---|---|---|
| Viewing path | Through the taking lens | Separate viewfinder |
| Focusing | On a focusing screen | Coincident-image rangefinder |
| Parallax at close distances | Effectively avoided | May require correction |
| Long telephoto lenses | Generally practical | More difficult to frame and focus |
| View during exposure | Brief blackout | Usually remains visible |
| Body construction | Requires a mirror box | Can be more compact |
An SLR shows the framing produced by the mounted lens. A rangefinder viewfinder usually uses frame lines to approximate the field of view.
This is one reason SLRs became widely used for macro, telephoto and technical photography.
No.
A Twin-Lens Reflex, or TLR, uses two lenses of similar focal length. One lens forms the photograph on the film, while the other sends an image to the focusing screen.
An SLR uses the same lens for both purposes.
Because the viewing and taking lenses of a TLR are physically separated, close-distance framing may be affected by parallax. An SLR avoids this separation by viewing through the taking lens.
No. SLR describes the camera mechanism rather than the film format.
The most familiar film SLRs use 135 film and produce a standard frame measuring approximately 24 × 36 mm.
Examples include:
Medium-format SLRs use roll film or interchangeable film backs.
Examples include:
These cameras may produce 6 × 4.5 cm, 6 × 6 cm, 6 × 7 cm or other medium-format images.
The larger film area usually requires a larger mirror, shutter mechanism and camera body.
Reflex viewing systems existed before the widespread use of miniature roll film.
The Kine Exakta, introduced in 1936, is commonly cited as one of the earliest production 35mm SLRs. The format developed rapidly after the Second World War.
By the 1960s and 1970s, the 35mm SLR had become one of the dominant interchangeable-lens camera designs. Manufacturers developed brighter viewfinders, through-the-lens metering, automatic exposure, motor drives and increasingly sophisticated lens systems.
Autofocus SLRs became widespread during the late 1980s and 1990s. The same architecture later continued in digital form as the DSLR.
The history of the SLR cannot be reduced to a single model. Different cameras represent different stages in the development of the system.
Introduced in 1959, the Nikon F established a modular professional system built around interchangeable lenses, viewfinders, focusing screens, film backs and motor drives.
It became closely associated with professional press and documentary photography.
The Nikon F3 combined Nikon's professional system design with an electronically controlled shutter and aperture-priority exposure.
Its long production period and extensive accessory system made it one of the best-known professional film SLRs.
The Canon AE-1 was introduced in 1976. It used electronic exposure control and was marketed to a broad audience of amateur photographers.
It remains one of the most recognisable Canon FD-mount cameras.
The Pentax K1000 is known for its straightforward manual controls. Its shutter can operate mechanically, while the battery powers the exposure meter.
Its simple layout led to extensive use in photography education.
The Olympus OM-1 demonstrated that a professional 35mm SLR system could be made smaller and lighter than many contemporary cameras.
Its compact body was supported by a broad range of Zuiko lenses and accessories.
Introduced in 1981, the Minolta X-700 combined manual exposure, aperture-priority operation and a programmed exposure mode.
It became the principal model of Minolta's final manual-focus SLR generation.
The Hasselblad 500C/M is a modular medium-format SLR using interchangeable film magazines, finders, focusing screens and leaf-shutter lenses.
Its reflex mirror and waist-level finder provide through-the-lens composition on a 6 × 6 cm frame.
The viewfinder shows the image formed by the mounted lens. This is particularly useful with wide-angle, telephoto, macro and special-purpose lenses.
The photographer focuses directly on the image produced at the film plane's optical equivalent.
Most SLR systems were designed around broad lens ranges. A single body could be used for landscapes, portraits, close-up work, architecture or sports.
The viewfinder presents the scene without an electronic display, image-processing delay or screen refresh rate.
Many professional SLRs accept interchangeable screens, prisms, motor drives, data backs, focusing accessories and specialised film backs.
The mirror box and prism require physical space. An SLR may therefore be larger than a rangefinder or compact camera using the same film format.
The optical image disappears while the mirror is raised.
Mirror movement can introduce vibration immediately before exposure. Some cameras include mirror lock-up or mirror pre-release for tripod work.
The mirror, shutter and viewing mechanisms must operate in a precisely timed sequence. Ageing foam, lubricants, springs and electronic components may require servicing.
Mirror and shutter movement normally make an SLR louder than a leaf-shutter rangefinder or compact camera.
A traditional optical viewfinder does not display the final brightness, colour response or grain of the film.
An SLR can be a useful camera for learning exposure and focusing because its controls are visible and directly connected to the photographic process.
A beginner can observe the effect of:
A fully mechanical model is not automatically the best choice. Aperture-priority cameras can make exposure faster while leaving focus, aperture and composition under the photographer's control.
Condition matters more than reputation. Before buying an older SLR, check:
Camera_DATA technical pages can be used to compare film format, mount, exposure modes, shutter specifications, dimensions and weight before choosing a model.
Look through the viewfinder while removing the lens, but do not touch the mirror or internal surfaces.
On most SLRs, a mirror will be visible inside the mount at an angle of approximately 45 degrees.
The camera will also normally have:
A prism-shaped top plate alone is not absolute proof. Some cameras use unusual viewfinder systems, and some medium-format SLRs use waist-level finders without a pentaprism.
The defining feature remains the movable reflex mirror behind the taking lens.
The importance of the SLR lies less in a single component than in the relationship between its components.
The lens forms the image. The mirror makes that image visible. The focusing screen provides a surface for evaluating focus. The prism presents it in a usable orientation. The shutter and mirror then move in sequence to expose the film.
This arrangement allowed one camera body to work with lenses of very different focal lengths while preserving direct through-the-lens composition.
Digital imaging changed the recording medium, but the reflex principle remained in use for decades through the DSLR. Film SLRs continue to provide a direct way to observe the mechanical and optical sequence behind a photograph.
Q: What does SLR mean on a camera? A: SLR means Single-Lens Reflex. The camera uses the same lens for viewing and exposure, with a mirror redirecting the image into an optical viewfinder.
Q: Why is it called a single-lens camera? A: "Single-lens" means that one optical path is used for composing and recording the photograph. It does not mean that the lens is permanently fixed to the camera.
Q: Why is the word "reflex" used? A: The word refers to the mirror that reflects light from the lens toward the focusing screen and viewfinder.
Q: Is an SLR a film camera? A: An SLR usually refers to a film camera, but the term describes the viewing mechanism. A DSLR uses the same reflex principle with a digital sensor.
Q: Does an SLR camera have a mirror? A: Yes. A movable mirror sits behind the lens during viewing and rises before the shutter opens.
Q: Why does the mirror move? A: The mirror must leave the optical path so that light can reach the film during the exposure.
Q: Can an SLR work without a battery? A: Some mechanical SLRs can fire their shutters without a battery, although their exposure meters may still require one. Electronically controlled SLRs usually need battery power to operate.
Q: Do all SLR cameras use interchangeable lenses? A: No. Interchangeable lenses are common, but they are not required by the definition of an SLR.
Q: Are all SLR cameras 35mm? A: No. SLRs were produced for 35mm, medium format, APS and several less common film formats.
Q: What is the difference between an SLR and a TLR? A: An SLR uses one lens for viewing and exposure. A TLR uses a viewing lens and a separate taking lens.
Q: What is the difference between an SLR and a rangefinder? A: An SLR shows the image through the taking lens. A rangefinder normally uses a separate viewfinder and focusing mechanism.
Q: Is an SLR better than a rangefinder? A: Neither design is universally better. SLRs are well suited to close focusing, telephoto lenses and precise through-the-lens composition. Rangefinders can be quieter, more compact and free from mirror blackout.
Q: Is an SLR better than a mirrorless camera? A: They provide different viewing experiences. An SLR uses a direct optical viewfinder, while a mirrorless camera provides an electronic preview from the sensor.
Q: What was the first SLR camera? A: Reflex cameras existed in several forms before 35mm photography became widespread. The 1936 Kine Exakta is commonly identified as one of the earliest production 35mm SLRs.
Q: Are film SLR cameras still usable? A: Yes. Many remain practical cameras if their shutters, mirrors, meters, film transports and light seals are in working condition.
Browse the Camera_DATA SLR database to compare cameras by manufacturer, production year, film format, lens mount, exposure system, weight and dimensions.
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An SLR is a camera that uses the same lens for composing the image and making the exposure. Inside the camera, a movable mirror redirects light from the lens into an optical viewfinder. When the shutter is released, the mirror rises and the light reaches the film.
The initials stand for Single-Lens Reflex. The term describes the viewing system, not the film size, the lens mount or the level of automation.
Most people associate SLR cameras with 35mm film such as the Nikon F3, Canon AE-1 or Pentax K1000. The same principle was also used in medium-format systems including the Hasselblad 500C/M, Mamiya RB67 and Pentax 67.
SLR stands for Single-Lens Reflex.
"Single-lens" means that the camera uses one optical path for both viewing and exposure. It does not mean that the camera has only one permanently attached lens. Many SLRs accept interchangeable lenses.
"Reflex" refers to the internal mirror. During composition, this mirror reflects — or redirects — the image upward toward the focusing screen and viewfinder.
This arrangement allows the photographer to observe the scene through the taking lens. Changes in focus, focal length and depth of field can therefore be viewed directly.
A camera is considered an SLR when it has three defining characteristics:
The recording medium may be photographic film or a digital sensor. A digital camera using the same mirror arrangement is normally called a DSLR, meaning Digital Single-Lens Reflex.
An SLR may be mechanical, electronic, manual-focus or autofocus. It may use a fixed lens or an interchangeable-lens mount. These features do not determine whether the camera is an SLR.
The operation of an SLR can be divided into two phases: viewing and exposure.
Before the shutter is released, light enters through the lens and reaches a mirror positioned at roughly 45 degrees.
The mirror reflects the light upward onto a focusing screen. The image then passes through a pentaprism or pentamirror before reaching the photographer's eye.
The prism corrects the orientation of the image. Without it, the view would appear laterally reversed or inconveniently oriented.
At this stage:
When the shutter button is pressed, the mirror rises out of the optical path.
The focal-plane shutter then opens for the selected exposure time. Light travels directly from the lens to the film, where the image is recorded.
Once the exposure is complete:
The entire cycle may take only a fraction of a second.
Although designs vary, most film SLRs contain the same basic optical and mechanical components.
The lens gathers and focuses light. On an SLR, it is used for both viewing and exposure.
The mirror redirects the image toward the viewfinder while the photographer is composing. It rises immediately before the shutter opens.
The focusing screen is the surface on which the lens forms a visible image. Depending on the camera, it may include a split-image rangefinder, microprism collar, grid or plain matte area.
Some professional SLRs use interchangeable focusing screens for different types of photography.
The pentaprism corrects the orientation of the image and directs it toward the eyepiece.
A pentamirror performs a similar function using mirrors rather than a solid glass prism. Pentamirror systems are generally lighter but may produce a less bright view.
The optical viewfinder allows the photographer to compose and focus without using a screen or electronic display.
Many SLR viewfinders also show exposure information, shutter speed, aperture, focus confirmation or metering indicators.
Most 35mm SLRs use a focal-plane shutter positioned directly in front of the film.
Some medium-format SLR systems use leaf shutters inside their lenses. The Hasselblad 500C/M is a well-known example.
The film is held flat at a precisely defined distance behind the lens mount. Correct alignment is essential for accurate focus.
The viewfinder becomes dark because the mirror must move out of the way before light can reach the film.
While the mirror is raised, it no longer reflects an image toward the focusing screen. The photographer therefore sees a brief blackout during the exposure.
At fast shutter speeds, this interruption may be barely noticeable. During a long exposure, the viewfinder remains dark until the shutter closes and the mirror returns.
Some early SLRs used non-instant-return mirrors. After an exposure, the viewfinder remained dark until the film was advanced or the shutter was recocked. The instant-return mirror later became standard on most SLR cameras.
Not necessarily.
The term SLR describes the optical mechanism. It does not specify the recording medium.
A traditional SLR records the image on photographic film. A DSLR uses a digital sensor but retains the mirror, focusing screen and optical viewfinder arrangement.
In everyday use, however, "SLR" often refers specifically to a film camera, while "DSLR" identifies its digital descendant.
Mirrorless digital cameras are not SLRs because they do not use a reflex mirror.
An SLR and a DSLR use a broadly similar viewing system. The main distinction is how the image is recorded.
| Feature | Film SLR | DSLR |
|---|---|---|
| Recording medium | Photographic film | Digital image sensor |
| Viewing system | Mirror and optical viewfinder | Mirror and optical viewfinder |
| Image review | After film development | Immediately on a screen |
| Storage | Individual film frames | Memory card |
| ISO | Determined mainly by the loaded film | Adjustable electronically |
| Image processing | Film and development process | In-camera or computer processing |
A DSLR is therefore not the opposite of an SLR. It is a digital form of the same basic camera architecture.
A mirrorless camera removes the reflex mirror and optical viewing path.
Instead of looking directly through the lens by means of a mirror and prism, the photographer views an electronic image from the sensor. This image appears on a rear screen or electronic viewfinder.
| Feature | SLR | Mirrorless camera |
|---|---|---|
| Reflex mirror | Yes | No |
| Viewfinder | Optical | Electronic or none |
| Viewfinder blackout | Caused by mirror movement | Depends on sensor readout |
| Body depth | Requires space for mirror | Can be shorter |
| View before exposure | Direct optical image | Electronic preview |
| Battery dependence | Varies by model | Normally essential |
The absence of a mirror allows shorter lens-to-sensor distances and fewer moving parts. An optical SLR viewfinder, however, does not require a live electronic display.
A rangefinder camera uses a separate viewing and focusing system. The photographer does not normally look through the taking lens.
This creates several practical differences.
| Feature | SLR | Rangefinder |
|---|---|---|
| Viewing path | Through the taking lens | Separate viewfinder |
| Focusing | On a focusing screen | Coincident-image rangefinder |
| Parallax at close distances | Effectively avoided | May require correction |
| Long telephoto lenses | Generally practical | More difficult to frame and focus |
| View during exposure | Brief blackout | Usually remains visible |
| Body construction | Requires a mirror box | Can be more compact |
An SLR shows the framing produced by the mounted lens. A rangefinder viewfinder usually uses frame lines to approximate the field of view.
This is one reason SLRs became widely used for macro, telephoto and technical photography.
No.
A Twin-Lens Reflex, or TLR, uses two lenses of similar focal length. One lens forms the photograph on the film, while the other sends an image to the focusing screen.
An SLR uses the same lens for both purposes.
Because the viewing and taking lenses of a TLR are physically separated, close-distance framing may be affected by parallax. An SLR avoids this separation by viewing through the taking lens.
No. SLR describes the camera mechanism rather than the film format.
The most familiar film SLRs use 135 film and produce a standard frame measuring approximately 24 × 36 mm.
Examples include:
Medium-format SLRs use roll film or interchangeable film backs.
Examples include:
These cameras may produce 6 × 4.5 cm, 6 × 6 cm, 6 × 7 cm or other medium-format images.
The larger film area usually requires a larger mirror, shutter mechanism and camera body.
Reflex viewing systems existed before the widespread use of miniature roll film.
The Kine Exakta, introduced in 1936, is commonly cited as one of the earliest production 35mm SLRs. The format developed rapidly after the Second World War.
By the 1960s and 1970s, the 35mm SLR had become one of the dominant interchangeable-lens camera designs. Manufacturers developed brighter viewfinders, through-the-lens metering, automatic exposure, motor drives and increasingly sophisticated lens systems.
Autofocus SLRs became widespread during the late 1980s and 1990s. The same architecture later continued in digital form as the DSLR.
The history of the SLR cannot be reduced to a single model. Different cameras represent different stages in the development of the system.
Introduced in 1959, the Nikon F established a modular professional system built around interchangeable lenses, viewfinders, focusing screens, film backs and motor drives.
It became closely associated with professional press and documentary photography.
The Nikon F3 combined Nikon's professional system design with an electronically controlled shutter and aperture-priority exposure.
Its long production period and extensive accessory system made it one of the best-known professional film SLRs.
The Canon AE-1 was introduced in 1976. It used electronic exposure control and was marketed to a broad audience of amateur photographers.
It remains one of the most recognisable Canon FD-mount cameras.
The Pentax K1000 is known for its straightforward manual controls. Its shutter can operate mechanically, while the battery powers the exposure meter.
Its simple layout led to extensive use in photography education.
The Olympus OM-1 demonstrated that a professional 35mm SLR system could be made smaller and lighter than many contemporary cameras.
Its compact body was supported by a broad range of Zuiko lenses and accessories.
Introduced in 1981, the Minolta X-700 combined manual exposure, aperture-priority operation and a programmed exposure mode.
It became the principal model of Minolta's final manual-focus SLR generation.
The Hasselblad 500C/M is a modular medium-format SLR using interchangeable film magazines, finders, focusing screens and leaf-shutter lenses.
Its reflex mirror and waist-level finder provide through-the-lens composition on a 6 × 6 cm frame.
The viewfinder shows the image formed by the mounted lens. This is particularly useful with wide-angle, telephoto, macro and special-purpose lenses.
The photographer focuses directly on the image produced at the film plane's optical equivalent.
Most SLR systems were designed around broad lens ranges. A single body could be used for landscapes, portraits, close-up work, architecture or sports.
The viewfinder presents the scene without an electronic display, image-processing delay or screen refresh rate.
Many professional SLRs accept interchangeable screens, prisms, motor drives, data backs, focusing accessories and specialised film backs.
The mirror box and prism require physical space. An SLR may therefore be larger than a rangefinder or compact camera using the same film format.
The optical image disappears while the mirror is raised.
Mirror movement can introduce vibration immediately before exposure. Some cameras include mirror lock-up or mirror pre-release for tripod work.
The mirror, shutter and viewing mechanisms must operate in a precisely timed sequence. Ageing foam, lubricants, springs and electronic components may require servicing.
Mirror and shutter movement normally make an SLR louder than a leaf-shutter rangefinder or compact camera.
A traditional optical viewfinder does not display the final brightness, colour response or grain of the film.
An SLR can be a useful camera for learning exposure and focusing because its controls are visible and directly connected to the photographic process.
A beginner can observe the effect of:
A fully mechanical model is not automatically the best choice. Aperture-priority cameras can make exposure faster while leaving focus, aperture and composition under the photographer's control.
Condition matters more than reputation. Before buying an older SLR, check:
Camera_DATA technical pages can be used to compare film format, mount, exposure modes, shutter specifications, dimensions and weight before choosing a model.
Look through the viewfinder while removing the lens, but do not touch the mirror or internal surfaces.
On most SLRs, a mirror will be visible inside the mount at an angle of approximately 45 degrees.
The camera will also normally have:
A prism-shaped top plate alone is not absolute proof. Some cameras use unusual viewfinder systems, and some medium-format SLRs use waist-level finders without a pentaprism.
The defining feature remains the movable reflex mirror behind the taking lens.
The importance of the SLR lies less in a single component than in the relationship between its components.
The lens forms the image. The mirror makes that image visible. The focusing screen provides a surface for evaluating focus. The prism presents it in a usable orientation. The shutter and mirror then move in sequence to expose the film.
This arrangement allowed one camera body to work with lenses of very different focal lengths while preserving direct through-the-lens composition.
Digital imaging changed the recording medium, but the reflex principle remained in use for decades through the DSLR. Film SLRs continue to provide a direct way to observe the mechanical and optical sequence behind a photograph.
Q: What does SLR mean on a camera? A: SLR means Single-Lens Reflex. The camera uses the same lens for viewing and exposure, with a mirror redirecting the image into an optical viewfinder.
Q: Why is it called a single-lens camera? A: "Single-lens" means that one optical path is used for composing and recording the photograph. It does not mean that the lens is permanently fixed to the camera.
Q: Why is the word "reflex" used? A: The word refers to the mirror that reflects light from the lens toward the focusing screen and viewfinder.
Q: Is an SLR a film camera? A: An SLR usually refers to a film camera, but the term describes the viewing mechanism. A DSLR uses the same reflex principle with a digital sensor.
Q: Does an SLR camera have a mirror? A: Yes. A movable mirror sits behind the lens during viewing and rises before the shutter opens.
Q: Why does the mirror move? A: The mirror must leave the optical path so that light can reach the film during the exposure.
Q: Can an SLR work without a battery? A: Some mechanical SLRs can fire their shutters without a battery, although their exposure meters may still require one. Electronically controlled SLRs usually need battery power to operate.
Q: Do all SLR cameras use interchangeable lenses? A: No. Interchangeable lenses are common, but they are not required by the definition of an SLR.
Q: Are all SLR cameras 35mm? A: No. SLRs were produced for 35mm, medium format, APS and several less common film formats.
Q: What is the difference between an SLR and a TLR? A: An SLR uses one lens for viewing and exposure. A TLR uses a viewing lens and a separate taking lens.
Q: What is the difference between an SLR and a rangefinder? A: An SLR shows the image through the taking lens. A rangefinder normally uses a separate viewfinder and focusing mechanism.
Q: Is an SLR better than a rangefinder? A: Neither design is universally better. SLRs are well suited to close focusing, telephoto lenses and precise through-the-lens composition. Rangefinders can be quieter, more compact and free from mirror blackout.
Q: Is an SLR better than a mirrorless camera? A: They provide different viewing experiences. An SLR uses a direct optical viewfinder, while a mirrorless camera provides an electronic preview from the sensor.
Q: What was the first SLR camera? A: Reflex cameras existed in several forms before 35mm photography became widespread. The 1936 Kine Exakta is commonly identified as one of the earliest production 35mm SLRs.
Q: Are film SLR cameras still usable? A: Yes. Many remain practical cameras if their shutters, mirrors, meters, film transports and light seals are in working condition.
Browse the Camera_DATA SLR database to compare cameras by manufacturer, production year, film format, lens mount, exposure system, weight and dimensions.