Single-lens reflex camera

In photography, a single-lens reflex camera (SLR) is a special kind of camera that uses a mirror and prism to let photographers see exactly what will be captured before taking a picture. These cameras became very popular for both professionals and everyday users from the late 1900s through the 1970s because they let people change lenses, measure light correctly, and frame pictures perfectly.

SLR cameras started in the 1930s and became widely used in the 1960s and 70s. They helped change how we take photos today. Even though digital cameras came along and changed things, SLR cameras were very important for many years. Now, newer cameras without mirrors are more common, but SLRs still matter in the history of photography. Unlike some other camera types, like twin lens reflex and rangefinder cameras, SLRs show the exact picture that will be taken. When you press the button to take a photo, the mirror moves out of the way so light can reach the film or sensor and capture the image.

History

Main article: History of the single-lens reflex camera

Before single-lens reflex (SLR) cameras, cameras with viewfinders had two separate light paths: one for the lens and film, and another for the viewfinder. This made close-up shots tricky because of a problem called parallax.

SLR cameras use a mirror and prism to let the photographer see exactly what the lens sees. When the picture is taken, the mirror moves out of the way so light can reach the film or sensor. SLR cameras became very popular because they let photographers see a clear, accurate view of their scene and allowed for interchangeable lenses. Even though digital cameras with screens have become common, SLR cameras are still used by professionals for their precision and clarity.

Digital SLRs

Main article: Digital single-lens reflex camera

Big camera companies like Canon, Nikon, and Pentax made digital SLR cameras (DSLRs). They used the same lens holders as their older film cameras. Sony took over Konica Minolta's camera part in 2006 and kept using their lens holder, even in cameras with a special mirror. Samsung made DSLRs using the Pentax lens holder. Olympus made a new system called the Four Thirds System, which Panasonic and Leica also used.

Contax made a DSLR called the Contax N-Digital, but it came out too late and cost too much to compete well. Even though it had a big sensor, it was too slow for some professional photographers.

Digital SLRs became much more popular than film SLRs in the early 2000s. But later, mirrorless cameras, like the mirrorless camera, took over as the main type of camera.

Optical components

A cross-section of the optical parts of a typical SLR camera shows how light goes through the lens, reflects off a mirror at a 45-degree angle, and appears on the focusing screen. Using a small lens and reflections inside a special glass block called a roof pentaprism, the image shows up in the viewfinder. When a picture is taken, the mirror moves up, the shutter opens, and the image is recorded on the film or sensor just like what the photographer sees.

This lets the photographer see exactly what will be captured, which makes SLRs different from other cameras.

Most small SLRs use a roof pentaprism or a penta-mirror to send light to the viewfinder. This was first used in the 1948 Duflex made by Jenő Dulovits and later in cameras like the 1955 Miranda T, Asahi Pentax, Minolta SR-2, Zunow, Nikon F, and the Yashica Pentamatic. Some SLRs could have different viewfinders, like a waist-level finder, used on cameras such as the Canon F1 and F1n, the Nikon F, F2, F3, F4, and F5, and the Pentax LX.

Another design uses a porro prism system, found in the Olympus Pen F, Pen FT, and Pen FV half-frame 35 mm SLRs. This design was also used in the Olympus EVOLT E-3x0 series, the Leica Digilux 3, and the Panasonic DMC-L1.

A right-angle viewer can attach to the top of most SLRs and digital SLRs, allowing viewing from a lower position. There are also viewers that let you see the image from a distance.

Shutter mechanisms

Main article: Shutter (photography)

Most modern single-lens reflex cameras use a special shutter called a focal-plane shutter. This shutter sits in front of the film and stops light from reaching it until you take a picture. Early shutters had two parts that moved across the film. When you took a picture quickly, these parts created a narrow opening that moved, letting light in just for a short time.

Some cameras use a different kind of shutter called a leaf shutter. This shutter has blades that open and close like a diaphragm and can be placed either in the lens or behind it. This type of shutter works well with studio lights because it can sync with flashes at any speed.

Further developments

Since the 1970s, single-lens reflex cameras have been the main tool for serious amateur photographers and professionals. Some photographers, especially for static subjects like architecture or landscapes, prefer view cameras because they allow more control over how the picture looks. For example, with special cameras like the Linhof SuperTechnika V, photographers can fix problems like "keystoning," where the lines of a building seem to lean or fall over in a photo. There are also special perspective correction lenses that help fix this problem in film cameras, and digital photos can also be fixed later using computer programs. Photographers can also use these cameras to take very close-up pictures, known as macro photography, by adjusting the camera in special ways.

Film formats

Main article: Film format

Early single-lens reflex cameras, often called SLRs, were made for large film sizes, but these are not popular today. Most SLR cameras work with different film sizes and digital formats. The 35 mm film format is commonly used because it has many options for film types, good image quality, and is affordable. It comes in rolls with different numbers of pictures, like 20, 24, or 36 images per roll. Medium format SLRs give even better image quality and are easier to fix up if needed.

A few SLRs were made for APS film, such as the Canon IX series and Nikon Pronea cameras. There were also SLRs for very small film formats like Kodak’s 110 film, including the Pentax Auto 110, which had lenses that could be changed. The Narciss camera is a small, metal 16 mm SLR made in the Soviet Union between 1961 and 1965.

Common features

SLR cameras often have special features like through-the-lens (TTL) metering and advanced flash control called "dedicated electronic flash". When you put a special flash into the camera's flash holder and turn it on, the camera and flash talk to each other. The camera sets the speed and how open the lens is. Many cameras measure the light coming through the lens to control how long the flash lasts. This is called TTL flash metering.

Some flashes can send out quick bursts of light to help the camera focus or talk to flashes that are not on the camera. A quick flash before the main picture is taken can help decide how long the main flash should last. Some cameras can also balance the flash light with the light already in the room. These features were added to top SLR cameras early on, while other types of cameras got them later.

Design considerations

SLR cameras let photographers see exactly what the lens sees, which helps them focus and frame their photos better than many other cameras. This is because they look through the same lens that will capture the image, so there are no differences between what they see and what the camera records.

SLR cameras often have lenses that let in more light, which is helpful in dim places and can make the background less clear so the subject stands out. They also have many types of lenses for different uses, like taking pictures from far away. However, SLR cameras are usually bigger and heavier than other cameras because of the mirror inside. This mirror can sometimes cause blurry photos when taking pictures quickly. Some cameras have special features to reduce this blur, but these can also make focusing harder.

Future

Digital single-lens reflex cameras became very popular in the early 2000s because they were easy to use and liked by many photographers. Around 2010, new mirrorless cameras started to appear, and they began to replace the older DSLR cameras.

By 2022, most big camera companies stopped making DSLR cameras and started making mirrorless ones instead. Mirrorless cameras have better autofocus and can have newer lenses because they don’t need a mirror. Some people still enjoy using film-based SLRs, but they are a smaller group now.

Main article: mirrorless systems