Single-lens reflex camera
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The single-lens reflex (SLR) is a type of camera that uses a movable mirror placed between the lens and the film to project the image seen through the lens to a matte focusing screen. Most SLRs use a roof pentaprism or pentamirror to observe the image via an eyepiece, but there are also other finder arrangements, such as the waist-level finder or porro prisms.
The cross-section (side-view) of the optical components of an SLR shows how the light passes through the lens assembly (1), is reflected by the mirror (2) 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 in the direction of the arrow, the focal plane shutter (3) opens, and the image is projected in the film (4) in exactly the same manner as on the focusing screen.
This feature separates SLRs from other cameras, as the user sees the image as it would be captured. This aids in accurately knowing the image beforehand.
Since the technology became widespread in the 1970s, SLRs have become the main type of camera used by dedicated amateur photographers and professionals.
History
Large format SLR cameras were first built in the early years of the 20th century.[[Citing sources citation needed]] Although the Soviet GOMZ sport (1935) was the first 35 mm SLR, it was the Ihagee Kine-Exakta (1936) that was truly influential. Further Exakta models, all with waist-level finders, were produced up to and during World War II. The first solution for an eye-level viewfinder was patented in Hungary during the war - more precisely, on August 23, 1943, by Jenő Dulovits. The first 35mm camera that had one implemented was the Duflex, designed by Dulovits. This camera utilised 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 serially produced SLR that employed a roof pentaprism was the East German Contax S, announced on May 20, 1949.
The Japanese further developed the SLR. In 1952, Asahi developed the Asahiflex and in 1954, the Asahiflex IIB. In 1957, Asahi Pentax introduced 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 (TTL) light metering came to the SLR in the early 1960s, with 1962's Topcon RE Super (spot metering) and 1964's Pentax Spotmatic (center-weighted average metering). Auto-exposure was next, introduced by Pentax in 1971's Electro Spotmatic and popularised with 1976's Canon AE-1 PROGRAM, one of the best-selling cameras of all time. Full program auto-exposure soon followed. The 1970s and 1980s saw steadily increasing use of electronics, automation and minaturization, including integrated motor driven film advance with the Konica FS-1 in 1979, and motor rewind functions.
Autofocus
The first TTL autofocus SLR was 1981's Pentax ME-F.[link] Nikon and Pentax developed models compatible with older lenses. SLRs also began to use electronic components like LCD (liquid crystal display) panels, IC chips, microcomputers. Pentax, Leica and Cosina continue to produce manual-focus SLR cameras today.
Digital SLRs
Canon, Nikon, Pentax and Minolta have developed digital SLR cameras compatible with their film SLR systems (though Konica-Minolta recently sold its SLR camera division to Sony who will continue manufacture), while Olympus has introduced a new digital-only SLR system, the Four Thirds system.
Format
SLR cameras have been produced for most film formats as well as digital formats. Most film SLRs use the 35 mm format, as this offers a good compromise between image quality, size, and cost. Medium format SLRs give a higher quality image when this is required. Digital SLRs (DSLRs) appeared on the market in the late 1990s and as of 2006 are used by many professional photographers as well as amateur enthusiasts. Early SLRs were built for large format photography, but this has largely died out. A small number of SLRs were built for the Advanced Photo System but this did not prove popular. SLRs were even built for film formats as small as 110, e.g. the Pentax Auto 110.
Common features
Other features found on many SLR cameras include through-the-lens (TTL) metering and sophisticated flash control. Many models on the market today actually measure the light that bounces off the film, and close the shutter when the picture has had enough exposure.Likewise, they can send out several short bursts of flash, determine the amount that comes back from the scene, then send out just the right amount of energy for a perfectly exposed photograph. Sophisticated cameras can even make it easy for the photographer to balance flash and available light for the desired look. While these capabilities are hardly unique to the SLR, manufacturers included them early on in the top models, whereas the best rangefinder cameras adopted such features later.
Advantages
Many of the advantages of SLR cameras derive from viewing the scene through the taking lens. The term Single Lens Reflex designates a type of camera which incorporates a viewing system where the subject is seen through the lens. This image is reflected on a mirror which passes through a prism that can be seen in the viewfinder. Cameras before SLR did not have this function, of course; subjects were seen through a viewfinder that was near the lens, making the photographer's view different from the lens' view. SLR cameras provided photographers with precision accuracy; they were seeing an image that would be exposed onto the negative exactly as it was seen through the lens. There is no parallax error, and exact focus can be confirmed by eye—otherwise hard for macro photography and when using telephoto lenses. The true depth of field may be seen by stopping down to the taking aperture, possible on all but the cheapest cameras. Because of the SLR's versatility, most manufacturers have a vast range of lenses and accessories available.
Compared to most fixed-lens compact cameras, the most commonly used and cheapest 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. This is commonly used in portrait photography.
Disadvantages
A disadvantage of the SLR is that you cannot view a scene at the moment the shutter captures the image. (One camera, the Canon Pellix, solved this problem by using a stationary beam splitting mirror but was not a commercial success.)
SLR cameras are usually heavier and larger than compact cameras because they have a pentaprism and mirror box.
The SLR's space-consuming mirror movement makes for difficulty in constructing wide angle lenses; rear lens elements cannot be close to the film plane. Retrofocus designs are required for wide-angle lenses; these are complex, large, and comparatively poorer in image quality.
The reflex mirror must retract before the shutter can open, which introduces some delay. Autofocus systems on modern SLRs introduce further delay, especially in lower light. The mirror's movement also causes vibration and noise, a problem when using longer lenses and longer exposures. Technology has reduced but not eliminated this problem, which again is worse in larger formats. To combat this, higher-end cameras offer the ability to lock up the mirror before the shot is taken. This eliminates the vibration but blacks out the viewfinder.
The SLR user cannot see anything outside the taking frame through the viewfinder, while with most rangefinder systems, this can be done. This helps in certain kinds of photography. Only higher-end SLRs show the full frame; typical coverage is 90%. Print labs generally crop an equivalent area, so it is less of a problem than it might otherwise be.
In the digital arena, the DSLR cameras have two further drawbacks compared to Compact or Bridge digital camera: the back panel display is usually unable to display live to assist with image composition and movie modes are generally unavailable.
Most of those issues are solved with digital SLR cameras with electronic viewfinder (EVF), which have many advantages over a classical mirror system, but the lower resolution of the viewfinder requires external monitor or viewfinder zoom-in for precise focus.
Notes
- ↑ See [Photography in Malaysia]'s [Contax History, Part II].
See also
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