DSLRs have significantly gained popularity not only among professional photographers but also photography enthusiasts and hobbyists. Offering a much larger sensor as compared to point and shoot cameras as well as semi SLRs , DSLRs offer considerably higher picture quality and offer flexibility in choosing lenses as per the requirement due to its interchangeable lens body. Recently, there’s another category of camera that also offers similar picture quality with its large sensor and also interchangeable lenses which you’ll not typically find in a point and shoot camera. There had been a lack of certainty for a while with what to call this category of camera, but the name mirrorless seems to have finally stuck and surprisingly it points to something which this camera doesn’t have. “A Mirror”

In order to understand what exactly this mirror does, we need to find out the basic structure of DSLR as shown in the given diagram. 

The diagram exhibits the process of capturing an image and essential parts within a SLR body. To understand the concept of capturing images via DSLRs in a simple manner, lets assume there is no mirror, prism or viewfinder inside the body of camera. In this case the light coming through lens in form of photons will be captured by sensor directly which is placed behind some filters (will be calrified later) and will produce the image. But there is a problem! We wont be able to see what the lens is seeing and hence cannot know exactly what the camera is capturing until the picture is taken. This can be overcome by live view and watching the action live on back of the camera screen but professional photographers rather prefer viewfinder for taking stills for better accuracy and to reduce flicker. So, mirror is introduced in front of the sensor which will reflect the light rays on to a prism and prism will further reflect it to the viewfinder from where the photographer is monitoring the frame. As the shutter is released this mirror flips up allowing the light rays to fall on to the sensor and hence the image is produced. 

Now that you know what a DSLR is, the term ‘mirrorless’ should make some sense. A mirrorless camera does not have a mirror in front of the sensor. That means there’s no need for a prism up above; there’s no need for a mirror chamber inside and hence the overall body size of mirrorless cameras reduces significantly. Typically mirrorless cameras have the live view screen at the back to track the frame live but some cameras have been introduced lately which offer electronic live view (Will be explained later in this article). The below table will give you detailed insight on difference between DSLRs & Mirrorless cameras based on certain factors.