What is a DSLR (Digital SLR) Camera?

DSLR stands for “Digital Single Lens Reflex”. It is a type of camera that uses a mirror to reflect light through a lens to an optical viewfinder. When the shutter is pressed, the mirror moves out of the way, and the reflected light hits the image sensor to take a picture. Although single-lens reflex cameras have been available in various shapes and forms since the 19th century with film as the recording medium, the first commercial digital SLR with an image sensor appeared in 1991. Compared to point-and-shoot and phone cameras, DSLR cameras use interchangeable lenses.

How a DSLR Works

When you look through a DSLR viewfinder on the back of the camera, whatever you see is passed through the lens attached to the camera, which means that you could be looking at exactly what you are going to capture. Light from the scene you are attempting to capture passes through the lens into a reflex mirror that sits at a 45-degree angle inside the camera chamber, which then forwards the light vertically to an optical element called a pentaprism. The pentaprism then converts the vertical light to horizontal by redirecting the light through two separate mirrors, right into the viewfinder. When you take a picture, the reflex mirror swings upwards blocking the vertical pathway and letting the light directly through. Then, the shutter opens up and the light reaches the image sensor. The shutter remains open for as long as needed for the image sensor to record the image. Then the shutter closes and the reflex mirror drops back to the 45 degree angle to continue redirecting the light into the viewfinder. The process doesn’t stop there. A lot of complicated image processing happens on the camera. The camera processor takes the information from the image sensor, converts it into an appropriate format, then writes it to a memory card. The whole process takes very little time and some professional DSLRs can do this 11+ times in one second.

Mirrorless Cameras

Many new cameras these days are mirrorless cameras, which means they lack the essence of the DSLR: the mirror. Mirrorless cameras do not have a mirror and prism mechanism, they do not use an optical viewfinder. Mirrorless cameras display a preview of the scene you are photographing by using the light hitting the digital sensor directly, and thus instead of an optical viewfinder as in DSLRs, mirrorless cameras have electronic viewfinders (EVF). Most DSLRs allow you to use a ‘Live View’ mode, however. In this mode, the mirror mechanism is permanently raised and the preview image is displayed on the rear view display. Thus, a DSLR can operate much like a mirrorless camera in live view, except that the preview is not through an electronic viewfinder.


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