DSLR (Digital single-lens reflex) Camera
Digital single-lens reflex cameras (also named digital SLR or DSLR) are digital cameras combining the parts of a single-lens reflex camera (SLR) and a digital camera back, replacing the photographic film. Features like live preview, HD video recording with contrast detection autofocus or ergonomic integration like dedicated film speed (ISO) buttons took further advantage of the digital image sensor. Although the term DSLR often refers to cameras that resemble 35 mm format cameras, some medium format cameras are also DSLRs.
Currently DSLRs are widely used by consumers and professional still photographers. Well established DSLRs currently offer a larger variety of dedicated lenses and other photography equipment, often using a larger image sensor format, often providing a higher dynamic range and signal to noise ratio. By contrast compact digital cameras and bridge cameras usually have smaller image sensors, which provides a larger depth of field. The newer mirrorless interchangeable-lens cameras (MILC) are beginning to compete with DSLRs while offering a more compact camera body.
Like SLRs DSLRs typically use interchangeable lenses (1) with a proprietary lens mount. A movable mechanical mirror system (2) is switched down (exact 45-degree angle) to direct light from the lens over a matte focusing screen (5) via a condenser lens (6) and a pentaprism/pentamirror (7) to an optical viewfinder eyepiece (8).
Focusing can be manual or automatic, activated by pressing half-way on the shutter release or a dedicated AF button. To take an image, the mirror swings upwards in the direction of the arrow, the focal-plane shutter (3) opens, and the image is projected and captured on the image sensor (4), after which actions, the shutter closes, the mirror returns to the 45-degree angle, and the built in drive mechanism re-tensions the shutter for the next exposure.
Compared to the newer concept of mirrorless interchangeable-lens cameras this mirror/prism system is the characteristic difference providing direct, accurate optical preview with separate autofocus and exposure metering sensors. Essential parts of all digital cameras are some electronics like amplifier, analog to digital converter, image processor and other (micro-)processors for processing the digital image, performing data storage and/or driving an electronic display.
Phase-detection autofocus
Main article: Phase detection autofocus
DSLRs typically use a phase detection autofocus system. This method of focus is very fast, and results in less focus "searching", but requires the incorporation of a special sensor into the optical path, so it is usually only used in SLR designs. Digicams that use the main sensor to create a live preview on the LCD or electronic viewfinder must use contrast-detect autofocus instead, which is slower in some implementations.
[edit]DSLRs with live preview
Main article: Live preview
Early DSLRs lacked the ability to show the optical viewfinder's image on the LCD display, a feature known as live preview. Live preview is useful in situations where the camera's eye-level viewfinder cannot be used, such as underwater photography where the camera is enclosed in a plastic waterproof case.
Olympus introduced the Olympus E-10 in the summer of 2000, which was the first DSLR with live preview – albeit an atypical design with a fixed lens. In late 2008, some DSLRs from Canon, Nikon, Olympus, Panasonic, Leica, Pentax, Samsung and Sony all provide continuous live preview as an option. Additionally, the Fujifilm FinePix S5 Pro[2] offers 30 seconds of live preview.
On all DSLRs that offer live preview via the primary sensor, the phase detection autofocus system does not work in the live preview mode, and the DSLR switches to a slower contrast system commonly found in point & shoot cameras. While even phase detection autofocus requires contrast in the scene, strict contrast detection autofocus is limited in its ability to find focus quickly, though it is somewhat more accurate.
Some live preview systems make use of the primary sensor to provide the image on the LCD (which is the way all non-DSLR digicams work), and some systems use a secondary sensor. Possible advantages of using a secondary sensor for live preview is to avoid additional noise that might result from the primary sensor heating up from continuous use and allowing faster auto-focus via phase autofocus.[3]
A new feature via a separate software package introduced from Breeze Systems in October 2007, features live view from a distance. The software package is named "DSLR Remote Pro v1.5" and enables support for the Canon EOS 40D and 1D Mark III.[4]
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DSLR (Digital single-lens reflex) Camera
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