What Are Mirrorless Cameras?

Back in 2013, when mirrorless technology was still in its infancy, and DSLRs still very much ruled the camera landscape, we predicted that the future was mirrorless. Back then, that generated a lot of discussions and arguments. Today, nobody would argue that point anymore.

But, just what is a mirrorless camera? Now, this question still generates some discussions, disagreements and arguments. And the reason it does is because when we take the dictionary definition of “mirrorless,” it simply means “lacking a mirror.” With this dictionary definition, every camera that does not have a mirror is therefore a “mirrorless” camera. Is that what the term mirrorless refers to when we talk about mirrorless cameras and mirrorless technology?

Many photographers, including some pros and reviewers, assume it does. That is an understandable mistake but unless we correct this misunderstanding and refrain from using the term mirrorless in this way, we risk losing the real meaning and importance of the term — and so we might as well stop using it if all cameras that lack a mirror is mirrorless.

Don’t forget the term mirrorless as far as applied to cameras did not exist until recently (2008). Before that, cameras that did not have a mirror were never referred to as mirrorless cameras. In fact, the term SLR (Single Lens Reflex) had to be introduced to differentiate the new (at the time of their introduction) cameras that had a reflex mirror, an optical viewfinder, and accepted one single lens that was interchangeable. The term mirrorless was applied to cameras only after Panasonic and Olympus revealed their mind-boggling intuition that the reflex mirror and optical viewfinder in a DSLR were now redundant and could be replaced by a high definition LCD and electronic viewfinder (EVF) using Real-time Live View. Without the need for a mirror and viewfinder housing, the DSLR could be shrunk in both size and weight, resulting in more compact and lighter cameras. To prove their point, Panasonic put out the G1 in 2008, the very first camera which had the term mirrorless applied to it.

Digital cameras like the Epson R-D1 (2004) and the Leica M8 (2006) were never off-shoot of DSLR models (they were instead digital versions of their optical rangefinder models), and do not have an EVF, so do not qualify for the term mirrorless.

But even before the term mirrorless (in its simple one-word version) became widely accepted, terms like EVIL (Electronic Viewfinder Interchangeable Lens), MILC (Mirrorless Interchangeable Lens Camera), DSLM (Digital Single Lens Reflex), Compact System Camera (CSC), mirrorless DSLR, and all sorts of variations floated around in the photography community, were discussed, debated and voted on at length in various forum boards.

In fact, the term mirrorless was not readily accepted by some influential people in the industry. For example, in 2014 the editors of the Technical Image Press Association (TIPA) announced that they were standardizing on the term Compact System Camera (CSC) instead of mirrorless because “CSC represents the essence of the new system much better than the term mirrorless, which in fact means nothing to people that do not know what a mirror has to do with a camera.” And, for some time, CSC it was in most publications. But the very next year, bowing to popular usage, TIPA itself started using the term “Mirrorless CSC” or “CSC/Mirrorless” to refer to these cameras. EISA (European Imaging and Sound Association) referred to these cameras as CSCs until 2017, switching to mirrorless in 2018, and dropping all reference to mirrorless in 2019 because mirrorless cameras had simply become the standard.

In another couple of years, when Nikon and Canon would have both brought out their flagship full-frame mirrorless cameras, DSLRs would become a thing of the past, and there would simply be no need to differentiate DSLRs from mirrorless cameras anymore. But until then, we do need to keep that term and its specifc definition intact.

What Is a Mirrorless Camera?

The term mirrorless DSLR, though technically an oxymoron, perhaps comes closest in defining what a mirrorless camera is. A mirrorless camera is a DSLR-level camera that, instead of using the traditional mirror, does away with the mirror and uses the image sensor itself paired with very high resolution EVF and LCD to allow the photographer to see exactly what is coming through the lens. It produces DSLR-level image quality, exhibits DSLR-level performance and accepts interchangeable lenses.

This definition automatically excludes all film cameras, all cameras that do not have an EVF (electronic viewfinder), and also all cameras that do not accept interchangeable lenses.

Think of it this way:

  • Start with a DSLR. So, you are getting DSLR-level image quality and performance to start out with.
  • Remove the mirror box and viewfinder pentaprism/pentamirror. Why? Because they are now redundant since the main raison-d’être of the mirror is to reflect (and hence the “reflex” of “Digital Single Lens Reflex“) the light coming through the lens into the viewfinder prism which would, through a series of reflections, present the image right side up to the photographer peering through the optical viewfinder. Replace them with an incredibly high resolution LCD and electronic viewfinder that can show us not only what is coming through the lens, but also what is actually hitting the image sensor, what the camera is going to save — and what our image would actually look like with exposure compensation, white balance and other filter effect applied, in real time.
  • Optimize it. With the bulky mirror and viewfinder prism removed, the camera can at last be made much slimmer, smaller and lighter. Add features that only an all-digital camera can have, and you end up with a camera that can match and even surpass a DSLR.

Mirrorless cameras might still not have successfully replaced DSLRs, but Panasonic and Olympus had an ace up their sleeves. They had standardized on a smaller Four-Thirds (4/3) image sensor that was about half the size of a 35mm full-frame image sensor, but was still big enough to give great image quality acceptable to pros. A smaller image sensor meant lenses could be smaller and lighter. This smaller and lighter camera and lens combo would appeal to many photographers tired of lugging around big, cumbersome and heavy camera and lenses. By getting rid of the redundant mirror, they called their new system Micro Four Thirds (MFT). So mirrorless cameras (based on the MFT system) quickly became very popular. Later, other camera companies applied mirrorless technology to cameras using APS-C image sensors. Sony introduced the first full-frame mirrorless cameras — and quickly cornered the pro and enthusiast mirrorless market.

So, what do we call a DSLR that has had its mirror removed? It’s still what it was before: a Digital, Single Lens, but the Reflex part is gone and to indicate that’s what has happened, we’ll instead replace the Reflex with Mirrorless. And hence we have the DSLM — Digital Single Lens Mirrorless (Panasonic still uses this term to refer to its mirrorless cameras) — aka the “Mirrorless” Interchangeable Lens Camera. (An Interchangeable Lens Cameras, or ILC, can refer to either a DSLR or a mirrorless camera since they both accept interchangeable lenses.) And with time, as we all got tired of saying (and writing) “Mirrorless Interchangeable Lens Camera,” we simply quietly dropped everything else and kept “mirrorless.”

TL;DR It is not correct to say that because a camera does not have a mirror, then it is automatically “mirrorless.” Using that literal dictionary definition, all cameras that do not incorporate a mirror would be “mirrorless.” Consider that the term “mirrorless” was specifically coined to differentiate a new group of DSLR-level cameras from the DSLRs, which have mirrors. So, mirrorless here refers to a specific group of DSLR-level digital cameras that give DSLR-level image quality and performance, but which do not need a mirror to allow the photographer to see exactly what is coming through the lens. A mirrorless interchangeable lens camera uses, of necessity, a large sensor to give DLSR-level image quality, has a high-definition LCD and EVF, and accepts interchangeable lenses.