Why Mirrorless

The year is 2024, yet phrases like “I am never going Mirrorless!” can still be heard across various online photography forums. Perhaps it is true that there are still certain affinity for DSLRs — after all, their image qualities are as good as they were 10 years ago — but in this post I want to explore the reason why so many people have been going interchangeable lens mirrorless that warranted such expression in the first place. I want to address the question: “Why Mirrorless?” Because in my view, Mirrorless cameras have so many advantages over DSLRs for both beginners and professionals alike and their only flaws are quickly being amended as well.

“The Bloody Obvious”

Perhaps it doesn’t need any explanations at this point, but for the sake of a argument, this has to be mentioned. Mirrorless cameras do not contain a mechanical mirror (or Pellicle mirror for that matter), nor a pentaprism optical viewfinder. The lack of these mechanical pieces leaves rooms for other uses, or simply not used at all. And as such, mirrorless cameras are often smaller, lighter, more resistant to fall, and the space saved in the camera bags means more lenses or accessories could be carried by the photographer.

The closer flange distance, or the distance between the mounting flange and the sensor plane, compared to DSLRs also makes lens making much easier. Lens designers no longer have to bend light around to focus the image onto the sensor that is so far away, and the less light you tamper with, the more light you have. So lenses designed for Mirrorless cameras can theoretically achieve a much higher aperture than DSLR lenses for similar weight class. And at same level of aperture, lenses designed for mirrorless are also smaller and lighter, with few exceptions. Just look at Sigma’s DG HSM lenses and their DG DN series and the point becomes very clear.

Autofocus

AF Sensor Coverage

Because the camera does not have a mirror, what you see is exactly what the camera sees, and as such, the camera no longer have to be restricted to the light reflected off the pellicle mirror or use a separate, tiny autofocusing sensor, instead, most of the main sensor can be used for contrast detect or phase detect autofocus. For example on latest Sony mirrorless cameras, like a6700, the AF sensor coverage is 100%, meaning every part of the image can be focused onto a subject, this number is simply impossible to achieve on pellicle mirror based autofocusing cameras, unless another sensor of the same size is used for autofocus under the mirror, which is incredibly impractical if not economically impossible to manufacture. This increase in AF area benefits all types of photography and videography.

AI Autofocus

The use of the main sensor for autofocusing also means that there are more data available for cameras to analyze, and the space saved by removing the mirror means more powerful image processor can be added. This combination allows something incredible, the camera not only can focus onto your selection points, but it can also analyze and autofocus onto specific parts of the image automatically. With Sony’s new AI autofocus, even the type of subject can be recognized by the camera. Now the camera can focus onto the eye of a cat for one shot and quickly focus onto the eye of a Northern Cardinal for another, even if the two creatures have their eyes located very differently on their bodies, if not having completely different types of eyes. This new intelligent AF greatly increases AF accuracy and efficiency for its users.

Your lenses are mine now

The most important benefit of the short flange distance is the possibility of adapting longer flange distance glasses onto the camera body. As such, Mirrorless cameras can almost always adapt DSLR lenses, even across manufacturers. For example, Sony E cameras could adapt Leica M mount glass, and Nikon Z cameras could use Canon EF lenses. In fact, Nikon Z mount’s flange distance is so short, that it could even adapt other Mirrorless lenses like Sony’s E mount lenses, making Nikon Z perhaps the future king of Mirrorless by it being able to use every lenses on the market, even the competitors’. Now it’s time to pull out grandpa’s 1960s lenses and give it a new spin!

EVF vs. OVF

Now let’s get to the crux of this post, and why I think the design that most people complained about on Mirrorless cameras — its electronic viewfinder — is actually one of its greatest strength.

Manual photographer’s paradise

On DSLRs, manual focusing is achieved via looking at the optical viewfinder and rotating the focus ring on the lens until you see a sharp image on your chosen focus point. The problem is, what you think is sharp 100 ft away might not actually be in focus. But you will have no way of knowing because you vision is limited to the focal length of the lens, unless you are an eagle. On a conventional mechanical SLRs, the pentaprism usually comes with focusing screen, and on that screen there is a split prism surrounded by a rough patch of microprism ring that when both matched correctly, gives you an indication that the center point of the image is in sharp focus. Yet on DSLRs, such focusing screen is usually not available and would conflict with its own focusing screen made out of groups of focusing points.

On Mirrorless, this is a nonissue due to two incredible functionalities – focus peaking and focus magnifier. With focus peaking, the sharp part of the image is highlighted and gives you a fast way to ascertain focus and depth of field. And the focus magnifier digitally zooms into the image and let you focus on an almost pixel level. These two tools completely changed the game for photographers who desire the precision or those who wish to use vintage lenses that only come with manual focus controls. Ironically, it is this modern camera that made using the vintage lenses most enjoyable.

Immediate feedback from exposure triangle

Again, because the EVF directly projects what the sensor sees, the user can see precisely the final image resulting from the exposure triangle setting. On an OVF, it is not possible to see the effect of ISO, one would have to rely on experience to know that ISO 12800 will produce a grainy looking image, or that 10 seconds exposure will lead to blurring on moving subjects. On an EVF, changing the ISO value or shutter speed directly influences the “brightness” of the scene on the viewfinder, allowing you to see bright image in low light environment or dark image in sunny conditions. The former is incredibly helpful for astrophotography, as faint stars that otherwise are too dim for human eye to see can be focused in real time with the help of EVF.

Light leak

A less talked about aspect of having an optical view finder is that light could come into the camera unexpectedly from behind as well. In long exposures, the usually negligible amount of light leaked from the viewfinder can over time compound to a level that could ruin an image. Although some professional cameras like Nikon offers a flap that can cover the viewfinder, it is however intrinsic to the design and is still less desirable compared to an EVF.

Danger to unwanted exposure

Recently when I started to explore solar photography I also came into this realization that could seriously prevent dslr being using in certain situations. Due to the optical nature of OVF, the light from the scenes reaches directly to your retina. In some cases this could pose serious danger. For example shooting into the sun not only subjects the sensor, but also your eye, to the harmful UV that could literally burn your retina and cause vision loss. And this is not just for solar photography, in any scenes that involve laser, there is also inherent danger to being inadvertently exposed to laser beam focused directly on the eye. With an EVF however, your eyes are safely protected by the sensor itself and are in no danger to any accidental exposures.

Improvements are still being made

Admittedly, Mirrorless cameras do have its shortcomings, like the reduction of battery life and the removal of on camera GPS module. The battery life in old Mirrorless cameras were dealbreakers to some, yet modern Mirrorless cameras are much better in this regard, reaching more than 600 shots on some Sony cameras, enough to last a day of shooting for even the savvy users. Other criticisms, like the low resolution of EVF compared to an OVF, were valid before the introduction of 9 million dots viewfinder of the Sony A7SIII and A7rV, but with more manufacturers stepping up their viewfinder resolutions and frame rates, there will soon be no complains on this area.

Closing Remarks

Hopefully by now you are more aware of the reasons why Mirrorless is the cameras of choice in the 2020s. Yet Mirrorless is not the endgame of camera technology, far from it, as the industry is already shifting to a “shutterless” design as seen on Nikon Z8 and Z9. And with the introduction of Sony’s fullframe global shutter sensor on the A9III, we can expect “shutterless” cameras to be the next Mirrorless and a new debate be written once again.