A digital single-lens reflex camera (also called a digital SLR or DSLR) is a digital camera combining the optics and the mechanisms of a single-lens reflex camera with a digital imaging sensor , as opposed to photographic film . The reflex design scheme is the primary difference between a DSLR and other digital cameras. In the reflex design, light travels through the lens, then to a mirror that alternates to send the image to either the viewfinder or the image sensor. The alternative would be to have a viewfinder with its own lens, hence the term single lens for this design. By using only one lens, the viewfinder presents an image that will not perceptibly differ from what is captured by the cameras sensor . Design of DSLR cameras 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) . Most of the entry level DSLRs use a pentamirror instead of the traditional pentaprism. 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 autofocus based on phase detection. This method allows the optimal lens position to be calculated, rather than found, as would be the case with autofocus based on contrast maximisation. Phase-detection autofocus is typically faster than other passive techniques. As the phase sensor requires the same light going to the image sensor, it is only possible with an SLR design and not with a camera having a separate viewfinder. Features commonly seen in DSLR designs Mode dial Digital SLR cameras, along with most other digital cameras, generally have a mode dial to access standard camera settings or automatic scene-mode settings. Sometimes called a PASM dial, they typically provide as minimum Program, Aperture-priority, Shutter-priority, and full Manual modes. Scene modes vary and are inherently less customizable. They often include full-auto, landscape, portrait, action, macro, and night modes, among others. Professional DSLRs seldom contain automatic scene modes because professionals understand their equipment and can quickly adjust the settings to take the image that they want. [ citation needed] Dust reduction systems Main article: Dust reduction system A method to prevent dust entering the chamber, by using a dust cover filter right behind the lens mount, was used by Sigma in its first DSLR, the Sigma SD9 , in 2002. [citation needed] Olympus used a built-in sensor cleaning mechanism in its first DSLR that had a sensor exposed to air, the Olympus E-1 , in 2003. [citation needed] Interchangeable lenses Main articles: Photographic lens and Lenses for SLR and DSLR cameras Canon EF-S 18-135mm APS-C Zoom lens The ability to exchange lenses, to select the best lens for the current photographic need, and to allow the attachment of specialized lenses, is one of the key factors in the popularity of DSLR cameras, although this feature is not unique to the DSLR design and mirrorless interchangeable lens cameras are becoming increasingly popular. Interchangeable lenses for SLRs and DSLRs (also known as Glass) are built to operate correctly with a specific lens mount that is generally unique to each brand. A photographer will often use lenses made by the same manufacturer as the camera body (for example, Canon EF lenses on a Canon body) although there are also many independent lens manufacturers, such as Sigma , Tamron , Tokina, and Vivitar that make lenses for a variety of different lens mounts. There are also lens adapters that allow a lens for one lens mount to be used on a camera body with a different lens mount but with often reduced functionality. Many lenses are mountable, diaphragm- and-meter-compatible, on modern DSLRs and on older film SLRs that use the same lens mount. However, when lenses designed for 35 mm film or equivalently sized digital image sensors are used on DSLRs with smaller sized sensors, the image is effectively cropped and the lens appears to have a longer focal length than its stated focal length. Most DSLR manufacturers have introduced lines of lenses with image circles optimized for the smaller sensors and focal lengths equivalent to those generally offered for existing 35 mm mount DSLRs, mostly in the wide angle range. These lenses tend not to be completely compatible with full frame sensors or 35 mm film because of the smaller imaging circle[1] and, with some Canon EF-S lenses , interfere with the reflex mirrors on full-frame bodies. HD video capture Since 2008, manufacturers have offered DSLRs which offer a movie mode capable of recording high definition motion video. A DSLR with this feature is often known as an HDSLR or DSLR video shooter. [2] The first DSLR introduced with an HD movie mode, the Nikon D90 , captures video at 720p 24 (1280x720 resolution at 24 frame/s ). Other early HDSLRs capture video using a nonstandard video resolution or frame rate. For example, the Pentax K-7 uses a nonstandard resolution of 1536×1024, which matches the imagers 3:2 aspect ratio. The Canon EOS 500D (Rebel T1i) uses a nonstandard frame rate of 20 frame/s at 1080p, along with a more conventional 720p30 format. In general, HDSLRs use the full imager area to capture HD video, though not all pixels (causing video artifacts to some degree). Compared to the much smaller image sensors found in the typical camcorder, the HDSLRs much larger sensor yields distinctly different image characteristics. [3] HDSLRs can achieve much shallower depth of field and superior low-light performance. However, the low ratio of active pixels (to total pixels) is more susceptible to aliasing artifacts (such as moire patterns) in scenes with particular textures, and CMOS rolling shutter tends to be more severe. Furthermore, due to the DSLRs optical construction, HDSLRs typically lack one or more video functions found on standard dedicated camcorders, such as autofocus while shooting, powered zoom, and an electronic viewfinder/preview. These and other handling limitations prevent the HDSLR from being operated as a simple point-and-shoot camcorder, instead demanding some level of planning and skill for location shooting. Video functionality has continued to improve since the introduction of the HDSLR, including higher video resolution (such as 1080p24 ) and video bitrate, improved automatic control (autofocus) and manual exposure control, and support for formats compatible with high-definition television broadcast, Blu-ray disc mastering [4] or Digital Cinema Initiatives (DCI). The Canon EOS 5D Mark II (with the release of firmware version 2.0.3/2.0.4. [5] ) and Panasonic Lumix GH1 were the first HDSLRs to offer broadcast compliant 1080p24 video, and since then the list of models with comparable functionality has grown considerably. The rapid maturation of HDSLR cameras has sparked a revolution in digital filmmaking, and the Shot On DSLR badge is a quickly growing phrase among independent filmmakers. Canons North American TV advertisements featuring the Rebel T1i have been shot using the T1i itself. An increased number of films, documentaries, television shows, and other productions are utilizing the quickly improving features. One such project was Canons Story Beyond the Still contest that asked filmmakers to collectively shoot a short film in 8 chapters, with each chapter being shot in only a couple of weeks and a winner was determined for each chapter, afterward the winners collaborated to shoot the final chapter of the story. Due to the affordability and convenient size of HDSLRs compared to professional movie cameras, The Avengers used five Canon EOS 5D Mark II and two Canon 7D to shoot the scenes from various vantage angles throughout the set and reduced the number of reshoots of complex action scenes. [6]
Posted on: Sun, 05 Oct 2014 00:23:07 +0000
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