Due, in part, to customer demand for mirrorless bodies, which are generally smaller, lighter and less expensive than their DSLR counterparts, there has been a huge uptick in demand for mirrorless cameras, and yet that demand hasn’t translated into a move by the main DSLR manufacturers to move into the space. This is largely due to the difficultly of transitioning an existing customer base over to a new platform—a mirrorless body would require a Canon or Nikon shooter to purchase new lenses for the new system—and, in part, to new engineering requirements for the new technology, which would take resources away from DSLR development.
For the DSLR manufacturers, there isn’t yet a reason to panic. The Sony a7R II, which is the current pinnacle of mirrorless camera development (see our review in this issue, "Shooting With Sony’s "Disruptive" a7R II"), is notable in that it has just caught up with pro-level DSLRs in some areas of operation, lags behind in many others and only just potentially surpassed the DSLR in a few areas. Even the vaunted a7R II falls short of pro-level DSLRs (and some advanced enthusiast models) in some key ways, and most of the rest of the field of mirrorless cameras lags behind that system in terms of performance and power because they’re aimed at the lower end of the market. That gives the major DSLR makers time to develop and perfect something mirrorless of their own before the competition overtakes them, at least from a performance standpoint.
What DSLR cameras do well, they do very well, and that’s partially the result of their form factor. The powerful processors, motors and circuitry required to churn out prize-winning images at 15 fps don’t yet fit inside a mirrorless body, and there’s a certain size expectation with mirrorless systems—after all, it’s the compact form that’s the competitive advantage of the mirrorless camera. If the mirrorless body has to increase to the size of a DSLR to fully compete, then what’s the point?
Room For Improvement
Look at the professional DSLR, and the most striking feature is its size. Anyone who has taken a pro DSLR to a birthday party or a kid’s soccer game knows the stares and odd looks the camera generates because of its enormity. But with the pro camera, the form follows the function, and the function of a pro DSLR is to operate at incredible speed under demanding conditions.
The mirror box—the "reflex" in single lens reflex—is one of the largest components of the body of an SLR. The mirror takes up so much room because it needs to be large enough to cover the full size of the sensor and to bounce light from the lens up to the viewfinder. It also needs to house the mechanism necessary to make sure this works at 1/8000th of a second at up to 15 times a second.
But the mirror box isn’t the largest part of the camera, just the part that the body is designed around. The frame of a DSLR is large because it’s chockfull of circuit boards, electronics, batteries and connectors. It’s a minor miracle of engineering that everything fits inside, and the companies use every millimeter of the housing to maximize the performance.
The most notable feature of a DSLR camera is the optical viewfinder, as it’s the through-the-lens focusing and composing prowess of the SLR that made it the most popular camera system in the world. The mirror of the DSLR bounces light up into an optical viewfinder and allows the photographer to see through the lens. A mirrorless system uses an electronic viewfinder (EVF) instead of an optical one, and while EVFs have some great features, many photographers swear by the quality of the image in an optical viewfinder. It’s the difference between looking at yourself in a mirror and looking at yourself on TV—it doesn’t matter how powerful the TV is, it’s not going to be the same as a mirror.
This becomes more important when working in low light. EVFs traditionally get grainy and pixelated under low-lighting conditions while optical viewfinders get dark, but no darker than the eye would see in the same conditions, give or take the amount of light passing through the lens.
Certainly, EVFs have some powerful advantages, but if you want the clarity of an optical viewfinder, by definition, you’re going to shoot with a DSLR.
Work with mirrorless cameras long enough, and you’re sure to hear someone say, "They’re not designed for sports photography." This complaint is usually leveled at the focus speed and capture rate of the systems (as well as the processing time, which I’ll discuss), and generally speaks the truth, though barriers are crumbling here faster than in other areas. The core of this argument currently revolves around full-frame mirrorless systems like the Sony a7R II, which has a top speed of 5 fps, while the Canon EOS-1D X has a frame rate of 14 fps in Super High Speed Mode.
In the APS-C arena, though, things start to get a bit more confusing. The Canon EOS 7D Mark II DSLR has a top speed of 10 fps, while the mirrorless Sony a6000 has a frame rate of 11 fps, and the mirrorless Samsung NX1 has a frame rate of 15 fps, faster than even the fastest pro DSLR.
That said, it’s unlikely we’ll see a full-frame mirrorless system come close to the frame rate of the Canon EOS-1D X or Nikon D4S until Sony releases a future generation of the Alpha system, one designed to toe up against the fastest pro systems—and, by then, who knows what Canon and Nikon will be able to do with the speed of their mirrors.
Another speed consideration is focus speed, and here, too, the DSLR is still king, if only for the time being. Pro DSLR systems have incredibly accurate phase-detection AF systems that currently are only challenged at all by the Sony a7R II and Samsung NX1. The rest of the phase-detection-based mirrorless camera market utilizes phase-detect systems that are much less robust than pro DSLRs, and many rely instead on contrast-detection autofocus systems, which fall far behind phase-detect systems in terms of focusing speed and the ability to track moving targets.
The powerful phase-detect focus systems in DSLRs is separate from the sensor, while in a mirrorless system, it’s integrated into the sensor itself. The mirror in the SLR flips to channel the incoming light to a dedicated focus sensor, which usually has its own processor. This powerful arrangement allows the camera to perform accurate, high-speed focus that sports and other photographers depend upon. Splitting the processing and focus sensor actually allows these systems to function more rapidly than when the imaging and focus points are combined on the sensor—at least today. As technology improves, these gaps will close, but today the top-end DSLR has more focus points with more coverage and more rapid processing than the mirrorless system.
Processors And Buffers
Pro-level DSLRs have bigger and more powerful processors, so these cameras can capture images at astounding rates because the processors are used to taking
the data from the sensors, converting them into a JPEG file or a RAW file and then pushing them to the camera’s buffers. The more powerful the processors, the faster the camera can capture images. The bigger the buffers (onboard memory), the more images that can be captured before the camera has nowhere to put them.
Mirrorless systems have less room, in general, which means smaller and/or fewer processors and smaller buffers. While mirrorless systems will get more powerful processors and buffers will be able to hold more in less space, these advantages apply to DSLRs, as well.
Power To The People
Professional DSLRs also have massive batteries, which not only drive the more energy-hungry mirrors the systems are built around, but also provide all-day energy that a mirrorless system currently can’t match. The Nikon D4S battery captures more than 3,000 shots on a charge, while the Sony a7 system captures around 300. The most power-friendly mirrorless systems only shoot around 500 frames before they conk out. This isn’t a minuscule difference either—a wedding photographer can burn through 300 images before the ceremony even starts, and a sports photographer can capture that many images in the first few innings.
The problem with power is compounded when photographers capture a mix of stills and video, as video capture is more processor-intensive and runs down the battery much faster than still photography. The result is a lightweight camera system that requires a handful or more of batteries, while the DSLR can complete a whole shoot with just one or two batteries.
Playing The Slots
A chief complaint about the Sony a7 series, and about mirrorless cameras, in general, is that they only have a single media slot. Professionals rely on dual media slots to keep shooting when one card fills up, in a situation where a card fails, or to capture RAW files on one card and JPEGs on another. The extra room afforded by the DSLR body allows the cameras to have multiple card slots, which gives them a tremendous advantage in professional workflows.
Professional DSLRs are sealed against the elements, protecting the camera from rain, dust, sand, dirt and other things that can get inside and destroy the delicate components and electronics. While a number of mirrorless cameras have a degree of resistance to moisture and contaminants, they’re not nearly as weather-sealed as the pro DSLR cameras. True weather sealing requires thick gaskets and couplings that increase the size of the housing—and small size is something that mirrorless systems strive to keep at all costs. For a photographer capturing a kayaker making a first descent on a waterfall or even a fashion shooter grabbing a clothing catalog shoot of a family frolicking in the surf, true waterproofing is vital.
The Future Of DSLRs
The current position of DSLRs relative to mirrorless cameras will change, and probably more quickly than we can imagine. (See "Misinformation" in this issue.) As both mirrorless and DSLR cameras evolve, we’ll see some features gain parity while some become more platform-defining. Only time will tell if there will even be DSLR cameras in the future, but for now, for many professionals, the top-end DSLR cameras have features that mirrorless cameras can’t touch. At least not today.
You can reach David Schloss on Twitter or Instagram @davidjschloss