Just a few years ago, mirrorless cameras constituted only about 5% of sales of ILC (interchangeable lens cameras).  This year, that number has grown to about 1/3rd of ILC sales, and will likely become the majority of ILC sales in the next year or two.  With the camera market in decline with the rise of smart phones, mirrorless won’t return the camera industry to its glory days.  But for enthusiast shooters, I expect mirrorless cameras to increasingly take over the market.   For some fans, this is a time of excitement.  Yet for some traditionalists, this is becoming a time of dread.

Some are doubting that mirrorless really will take over.  But I have little doubt.   The dSLR camera (digital single lens reflex) was a temporary solution to a problem that no longer exists.  The compromises of a dSLR camera now outweigh the benefits.  This temporary solution was dominant in the camera industry for over 50 years.   It was an ingenious solution to technological limitation.   A traditional camera operated with a lens that focused the light on to a strip of film.  But how could the photographer see the same thing that the lens/film was seeing???   And thus, the SLR used mirrors to reflect the image that was coming in from the viewfinder, and a complex mechanical system would then lift the mirror just moments before taking the image.

Over the years, this system was improved.   The mirror could be flipped up and down multiple times per second.  The light did not just get reflected into a viewfinder for the photographer to view, it also got reflected for use by a dedicated autofocus system, which was refined and perfected over the years.

Then came the advent of the digital era, over 20 years ago.   The potential change in the equation was immediately apparent.  The image was no longer being focused on to a strip of film.  The image was now being reflected on to a digital sensor.  In addition to recording the image as a photograph, the sensor could also be used to generate a video feed — so that the photographer could see the same image that was being seen by the sensor.

Yet, with early digital, serious cameras continued to use the SLR design, a mirror mechanism reflected the light to a dedicated autofocus system and optical viewfinder.   But every point and shoot camera was essentially “mirrorless.”  The technology just was not appropriate for serious shooters:  large sensors could not be read fast enough to generate a quality video feed and also shoot stills.   There was no mature focus system that could replace the focus system used in SLRs.   But shortly after the first dSLRs, we did start to have the first mirrorless cameras.  They used smaller sensors and were promoted on size advantages.

It was only over the last few years that camera makers such as Sony and Fuji started making ILC cameras with the same sized sensors found in Nikon and Canon dSLRs.   The cameras promised the potential for advancements, but it was not until now that those advancements have really been realized.  dSLRs now have more drawbacks than strengths.   Canon started getting serious about mirrorless in 2017.  Canon and Nikon are both expected to get much more serious in 2018.  At that point, mirrorless market share will really take off.

It is not that dSLRs are poor products.  And it’s not that today’s mirrorless are vastly better.

So why will mirrorless replace dSLR?

Size

DSLRs required a certain size in order to accommodate the entire mirror mechanism.   Removal of the mirror mechanism immediately allows for a smaller design.   Some traditionalists will argue that the size advantages are exaggerated.  They are right:  If the sensor is the same size, the camera/lens size is not going to be significantly smaller.  But cameras have gotten huge, even slight size savings can be an advantage for some buyers.

Other traditionalist buyers will argue that mirrorless cameras are too small, that they can’t balance their large lenses as well.   Personally, I think this is just an absurd stubborn argument.   If you have a 2,000 gram lens, it isn’t going to make a huge difference whether you put it on a slightly thicker 800 gram body or a slightly thinner 650 gram body.   If there is any validity to this argument, there is nothing to stop a manufacturer from producing larger body mirrorless.    You can always take a mirrorless camera and make it thicker/bigger, but you can’t always take a dSLR and make the design any smaller.

Mechanical Complexity and Price

The mirror system required by a dSLR is incredibly complex.   With extreme precision, this mirror must be flipped up and down, reflecting the image to another high quality pentamirror or pentaprism system.   The removal of this system is a win-win for the manufacturer and customers.   Less mechanical complexity means less that can break.  It also means much cheaper to manufacture.  Which means more profit for the manufacturer while also giving the customer lower prices.

Most dSLR Optical viewfinders are horrible

Traditionalists will exclaim how they hate the electronic viewfinders of mirrorless and prefer optical viewfinders.  The best dSLR cameras, often priced over $2,000, do indeed have fantastic optical viewfinders that are large and bright.

But consumer dSLRs, under $1,000, tend to have truly dreadful viewfinders.  As noted above, it is an expensive mechanism.  So cheaper dSLRs cut costs with tiny dark tunnel-like viewfinders.  Yet, even mid-level mirrorless cameras can have large bright electronic viewfinders.

Comparing the best optical viewfinder to the best electronic viewfinders, you will have legitimate fans of each.   An optical viewfinder does not drain the battery.  It can feel like a more immediate way of looking at a scene, and it can be easier to see areas of high contrast.   Yet an electronic viewfinder enables functions that are impossible or nearly impossible in an optical viewfinder.   That includes reviewing menus and images without removing your eye from the viewfinder, getting a simulated exposure in the viewfinder, viewing the histogram in the viewfinder, etc.

And the flagship Sony A9 already has a game changing viewfinder feature that is only possible with electronic viewfinders.   When shooting continuously, the optical viewfinder must, by necessity, black out as the mirror flips up and down between images.   The A9 has no black out — The photographer gets an uninterrupted view of the scene, even shooting at 20 frames per second, with no blackout.   Eventually this technology will filter down to cheaper models.  It is a technology that a dSLR will never match.

Benefits of removing the flipping mirror

As noted above, the flipping mirror causes a blackout between images.  That isn’t the only drawback of the flipping mirror.    It also adds vibration to the camera and vibration can reduce the quality of images.   Thus, a mirrorless camera can get rid of this vibration leading to higher effective resolution.

One must also consider the mirror in conjunction with the mechanical shutter, which closes over the sensor with each image.   As processing speed improves, cameras like the A9 are largely getting rid of the mechanical shutter.  Once both the mechanical shutter and mirror are gone, it will be further cost savings and further benefits.

Removal of the flipping mirror and the mechanical shutter allow for completely silent shooting.  They also allow for uninterrupted autofocus.  As it stands, a dSLR focuses first, and then the focus system essentially is disrupted for a fraction of a second as the mirror flips up.  In a mirrorless system which also uses an electronic shutter, the autofocus system has the potential to be continuous for more reliable autofocus.

Better Autofocus

This is the controversial one.  As mentioned above, autofocus systems were refined over many years in dSLRs.   Mirrorless requires an autofocus system to be integrated into the sensor.  For many years, these systems simply were slower than dSLR systems.

Now, with the current generation, mirrorless autofocus systems have surpassed dSLRs.   Traditionalists will claim that the Nikon D5 is the best AF tracking camera there is.  Even if they are right, the best mirrorless have the following AF advantages:

• More precise autofocus.   dSLRs are notorious for focus shift issues, back focus, front focus.  Lots of things within the camera and lens design can cause focus to be off by a few millimeters.  As we move to ultra high resolution cameras, these slight focus misses become more apparent.  Since mirrorless test focus right on the sensor, mirrorless autofocus can be more precise and exact.
• Focus areas covering more of the frame:  Due to the mechanics of measuring focus with the light reflected from the mirror, dSLRs mostly have to group the focus points towards the center of the frame, especially with full frame cameras.   Mirrorless can extend focus points over a far greater area of the frame.
• On sensor focus systems can more intelligently recognize scenes, allowing for superior face detection.  In fact, the best mirrorless systems can automatically locate and track the nearest eye.   As a portrait shooter, for years I would use the “focus and recompose” method for shooting sharp portraits.  Mirrorless completely changes my workflow — I can just let the camera lock on to the eye automatically.
• Manual focus aids:   Get extreme magnification of the scene or get color-coded focus peaking (showing bright colored lines along in-focus areas) to make manual focus super easy.

Traditionalists will hold on to the claim that dSLRs still have been tracking autofocus.   The reality is, they are very very close in this regard.  And with the ability to continuously assess autofocus without mirror flap disruptions, mirrorless camera autofocus tracking will likely surpass dSLR very soon.

dSLRs are ALREADY Mirrorless

Huh?? What did I just say?  Have I lost my mind??   The reality is, every modern dSLR already has “mirrorless mode.”  The mirror must be flipped up in order to take video.   dSLRs all have a “live view” mode — again, the mirror is flipped up.  In these modes, the camera is operating entirely as a mirrorless camera but without a viewfinder.  The dSLR is no longer using the mirror based autofocus system.  Instead, it is using the sensor based autofocus system just like a mirrorless camera.

The only question is whether they have a good on-sensor autofocus system or a bad system (like early mirrorless cameras).

So once you have a dSLR camera where the on-sensor focus system is actually better than the mirror-viewfinder based autofocus system, then what really is the point of even having the mirror-viewfinder based autofocus system?  As noted above, the mirror system add size, complexity and cost to the camera.  Why add the size, complexity and cost if you aren’t really getting any benefit???  I propose that a mere subjective preference by some users for an optical viewfinder will not be enough reason to keep dSLRs in business.

So why haven’t mirrorless taken over yet?

Some traditionalists will say, “I’ve been hearing about mirrorless for years.. but dSLRs are still the majority….. nothing is going to change any time soon.”

First off, it is only recently where mirrorless autofocus system could evenly match and even surpass dSLRs.  More important is the issue of momentum.   Traditional dSLR lenses are not optimized for mirrorless cameras.   Nikon doesn’t even currently make mirrorless cameras.  Canon only makes aps-c mirrorless cameras, no full frame.   So if you have a big collection of Canon or Nikon lenses, you’re not going to just switch your entire system at the drop of a hat.  Additionally, there is still a perception in some regions that “dSLRs are the best.”

In the beginner photography classes I teach, there is sometimes a perception that dSLRs are “better” because they look like the stereotype of what one expects of a great camera, while mirrorless may look less serious.   These beginners heard for many years, “Nikon and Canon dSLRs are the best” and that has stuck in their head.  I’ve had students say things to me like, “my camera is really good, right?  It’s a Canon.”   They don’t know which Canon.  It may be a cheap bridge camera which looks a bit like a dSLR but is actually a point and shoot.  But because it has the Canon label and looks like a dSLR, they assume it must be a good camera.

Thus, change can be slow.  The camera market is shrinking, so you don’t have lots of incoming young new users who are quick to adapt new technology.   This slows down the change even more.  But make no mistake, the change is happening now before our eyes.   Mirrorless is on the verge of taking over what is left of the serious camera market.