What is DSLR (Digital Single-Lens Reflex)?

             Digital Single-Lens Reflex

DSLR is a digital camera that uses mirrors to direct light from the lens to the viewfinder, which is a hole on the back of the camera that you look through to see what you are taking a picture of.

• With an SLR camera, you see exactly what the lens sees
• You can change the lens on a digital SLR
• Digital SLRs have large image sensors that produce high-quality photos
• An SLR has a near-zero lag time, and is ideal for action photography

The light we see when we look through the viewfinder on our SLR camera and the light that hits the image sensor when we make an exposure comes through a single lens. This might seem obvious until you consider that not all cameras work this way.Some cameras have two lenses – one through which the exposure is made and another, either above or to one side, that enables you to see through and compose the photograph.Essentially, since there is only a single lens, “what you see is what you get.”

         Reflex gives us a clue as to how using the same lens to see through and also make the exposures is possible – reflection.     

         SLR camera mirror------- there is a mirror placed at a 45 degree angle directly in the path of the light through the lens. This reflects the light upwards where it enters another reflective assembly above the mirror which corrects the image (remember, it’s been reflected!) and then directs it out of the viewfinder and into your eye.

 Normal light path (red line, simplified) through a DSLR camera.

1. Think of it like a periscope in reverse – in principle it’s not really that different. But what happens when we want to make an exposure? Well, quite simply, the mirror moves out of the way when you press the shutter button and lets the light hit the sensor behind it.
2. Light path (blue line) to the sensor when the shutter button is pressed. Imagine that the mirror is moved up and out of the way.

When SLR cameras first appeared one of the main advantages was that they were significantly less bulky than some of their twin-lens alternatives. Today, with the advent of small mirror-less cameras, this is no longer true and SLR cameras are among the largest a typical consumer would consider buying.

They are, however, still a popular choice and indeed the preferred choice among professionals. There are numerous reasons for this – but the main reason specifically related to the SLR design is that when you look through the viewfinder, what you see is very close to what you get in the exposure. This is a very important advantage for working photographers and for those who simply do not wish to deal with any potential margin for error.