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A digital single-lens reflex camera (digital SLR or DSLR) is a digital camera that combines the optics and the mechanisms of a single-lens reflex camera with a digital imaging sensor.

The reflex design scheme is the primary difference between a DSLR and other digital cameras. In the reflex design, light travels through the lens and then to a mirror that alternates to send the image to either a prism, which shows the image in the viewfinder, or the image sensor when the shutter release button is pressed. The viewfinder of a DSLR presents an image that will not differ substantially from what is captured by the camera's sensor but presents it as a direct optical view through the lens, rather than being captured by the camera's image sensor and displayed by a digital screen.

DSLRs largely replaced film-based SLRs during the 2000s.

Design

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, by twisting the focus on the lens; or automatic, activated by pressing half-way on the shutter release or a dedicated auto-focus (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 with 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 microprocessors for processing the digital image, performing data storage and/or driving an electronic display.

Phase-detection autofocus

The reflex design scheme is the primary difference between a DSLR and other digital cameras. In the reflex design, light travels through the lens and then to a mirror that alternates to send the image to either a prism, which shows the image in the viewfinder, or the image sensor when the shutter release button is pressed. The viewfinder of a DSLR presents an image that will not differ substantially from what is captured by the camera's sensor but presents it as a direct optical view through the lens, rather than being captured by the camera's image sensor and displayed by a digital screen.

DSLRs largely replaced film-based SLRs during the 2000s.

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, by twisting the focus on the lens; or automatic, activated by pressing half-way on the shutter release or a dedicated auto-focus (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 with 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 microprocessors for processing the digital image, performing data storage and/or driving an electronic display.

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 was previously only possible with an SLR design. However, with the introduction of the focal-plane phase detect autofocusing in mirrorless interchangeable lens cameras by Sony, Fuji, Olympus, and Panasonic, cameras can now employ both phases detect and contrast-detect AF points.

Features commonly seen in DSLR designs

Focusing can be manual, by twisting the focus on the lens; or automatic, activated by pressing half-way on the shutter release or a dedicated auto-focus (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 with 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 microprocessors for processing the digital image, performing data storage and/or driving an electronic display.

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 was previously only possible with an SLR design. However, with the introduction of the focal-plane phase detect autofocusing in mirrorless interchangeable lens cameras by Sony, Fuji, Olympus, and Panasonic, cameras can now employ both phases detect and contrast-detect AF points.

Features commonly seen in DSLR designs

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 modes such as program, aperture-priority, shutter-priority, and full manual modes. Scene modes vary from camera to camera, and these modes are inherently less customizable. They often include landscape, portrait, action, macro, night, and silhouette, among others. However, these different settings and shooting styles that "scene" mode provides can be achieved by calibrating certain settings on the camera. Professional DSLRs seldom contain automatic scene modes, as professionals often do not require these.[citation needed]

Dust reduction systems

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] (all previous models each had a non-interchangeable lens, preventing direct exposure of the sensor to outside environmental conditions).

Several Canon DSLR cameras rely on dust reduction systems based on vibrating the sensor at ultrasonic frequencies to remove dust from the sensor.[1]

Interchangeable lenses

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