Single-lens reflex camera
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).
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 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.
The viewfinder can include a matte focusing screen located just above the mirror system to diffuse the light.
Nearly all inexpensive compact digital cameras now include an LCD preview screen allowing the photographer to see what the CCD is capturing.
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.
Sony continues using the Minolta AF lens mount in their DSLRs, including cameras built around a semi-transparent fixed mirror.
Olympus, on the other hand, chose to create a new digital-only Four Thirds System SLR standard, adopted later by Panasonic and Leica.
The digital single-lens reflex camera have largely replaced film SLRs design in convenience, sales and popularity at the start of the 21st century.
A cross-section (or 'side-view') of the optical components of a typical SLR camera shows how the light passes through the lens assembly, is reflected by the mirror placed at a 45-degree angle, and is projected on the matte focusing screen.
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.
Most 35 mm SLRs use a roof pentaprism or penta-mirror to direct the light to the eyepiece, first used on the 1948 Duflex[4] constructed by Jenő Dulovits and patented August 1943 (Hungary).
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.
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.
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 1⁄4000 second for non-sync shooting, and 1⁄250 with x-sync.
If the shutter is part of a lens assembly some other mechanism is required to ensure that no light reaches the film between exposures.
Hasselblads use an auxiliary shutter blind situated behind the lens mount and the mirror system to prevent the fogging of film.
Some manufacturers of medium-format 120 film SLR cameras also made leaf-shutter lenses for their focal-plane-shutter models.
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.
A small number of SLRs were built for APS such as the Canon IX series and the Nikon Pronea cameras.
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.
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.
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.
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.
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.
More recently, Sony have resurrected the pellicle mirror concept in their "single-lens translucent" (SLT) range of cameras.
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.
As of 2022, all the major camera brands (Except Pentax) ceased development and production of DSLRs and moved on to mirrorless systems.
