Portal: Large_format_camera_lens.png A digital single-lens reflex camera (digital SLR or DSLR) is a digital camera that uses an automatic mirror system and pentaprism or pentamirror to direct light from the lens through the viewfinder eyepiece.

The basic operation of a DSLR is as follows: for viewing purposes, the mirror reflects the light coming through the attached lens upwards at an approximately 90 degree angle. It is then reflected by the pentaprism to the photographer's eye. During exposure (when the photograph is taken), the mirror swings upward, and a shutter opens, allowing the lens to project light onto the image sensor.

Brief difference between a DSLR and a Digicam

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The reflex design scheme is a major difference between a DSLR and an ordinary digital camera (digicam), which typically exposes the sensor constantly to the light projected by the lens, allowing the camera's screen to be used as an electronic viewfinder.

In contrast, the mirror arrangement in a DSLR usually precludes the ability to view the scene on the liquid crystal display (LCD) before the photograph is taken. However, many newer DSLR models feature live preview, allowing the LCD to be used as a viewfinder in the same way as a normal digicam, although with certain limitations and with the optical viewfinder disabled.

In most other respects, a DSLR is similar in principle and operation to a standard (non-SLR) digital camera.

DSLR design principles

[[image:SLR cross section.svg

A camera based on the single-lens reflex (SLR) principle uses a mirror to show in a viewfinder the image that will be captured. The cross-section (side-view) of the optical components of an SLR shows how the light passes through the lens assembly (1), is reflected into the pentaprism by the reflex mirror (which must be at an exact 45 degree angle) (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 is projected through the eyepiece (8) to the photographer's eye. Focusing is either automatic, activated by pressing half-way on the shutter release or a dedicated AF button, as is mainly the case with an autofocusing film SLR; or manual, where the photographer manually focuses the lens by turning a lens ring on the lens barrel. When an image is photographed, 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 sensor (4), after which actions, the shutter closes, the mirror returns to a critical 45 degree angle, and the diaphragm reopens and the built in drive mechanism retensions the shutter for the next exposure. There is often a ring of soft material around the focusing screen, which helps to both cushion the impact of the mirror slapping up and help seal the mirror box from light entering through the eye piece. Some high end cameras incorporate a shutter into the eyepiece to further eliminate light that may enter there during long exposures.