Most digital single-lens reflex cameras (digital SLR or DSLR) are digital cameras that use a mechanical mirror system and pentaprism to direct light from the lens to an optical viewfinder on the back of the camera.
DSLRs are often preferred by professional still photographers because they allow an accurate preview of framing close to the moment of exposure, and because DSLRs allow the user to choose from a v
ariety of interchangeable lenses. Most DSLRs also have a function that allows accurate preview of depth of field.
Many professionals also prefer DSLRs for their larger sensors compared to most compact digitals. DSLRs have sensors which are generally closer in size to the traditional film formats that many current professionals started out using. These large sensors allow for similar depths of field and picture angle to film formats, as well as their comparatively high signal to noise ratio.
The term DSLR generally refers to cameras that resemble 35 mm format cameras, although some medium format cameras are technically DSLRs.
Mainstream DSLRs (full-frame or smaller image sensor format) are currently produced by Canon, Leica, Nikon, Olympus, Pentax, Samsung, Sigma, and Sony. Phase One, Leaf, Linhof, Pentax, Hasselb
lad and Mamiya, amongst others, produce expensive, high-end medium-format view-cameras.
DSLR design principles
1. 4-element lens
2. Reflex mirror
3. Focal-plane shutter
4. Image sensor
5. Matte focusing screen
6. Condenser lens
7. Penta
DSLR design principles
1. 4-element lens
2. Reflex mirror
3. Focal-plane shutter
4. Image sensor
5. Matte focusing screen
6. Condenser lens
7. Penta
prism
8. Eyepiece
8. Eyepiece
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 mirr
or (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 the 45-degree angle, the diaphragm reopens, and the built in drive mechanism re-tensions 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 helps seal the mirror box from light entering through the eye piece.[1] Some high-end cameras incorporate a shutter into the eyepiece to further eliminate light that may enter there during long exposures
