- Can be made smaller and lighter than DSLR.
- Many mirrorless cameras use APS-C sized sensors – the same as in most DSLR, which are responsible for high image quality.
- Viewfinder can be anywhere on camera. There is no more need to keep it in line with lens; they can be on the left side like on rangefinder cameras. Most photographers agree it’s more practical and easier to use them that way.
- Live view previews image before it is taken; this is a completely new approach which allows more control over final image.
- Live histogram on LCD or in viewfinder.
- Contrast AF is more precise than phase detect system. It measures focus directly on the place where the final image will be taken – sensor. Forget about AF point misalignment that plagues some modern DSLR cameras.
- Black and white effect in viewfinder; this allows all the B&W shooters to see how the scene looks in B&W before the exposure.
- Ability to frame in low light. Remember how the optical viewfinder gets unusable in really dark environments? You eyes are just not sensible enough to see in the dark, but digital sensor is not. It can crank up the ISO and boost the brightness to aid you with framing and focusing.
- Electronic viewfinders can be big. Really big. Optical viewfinders were limited by mirror and pentaprism size, especially on cheaper cameras with APS-C or 4/3 sensors. I still gives me headaches when I remember the tiny optical tunnel I had to use on Olympus E500. Even cheap mirrorless cameras can be equipped with decently sized viewfinders.
- Flawless manual focus. Focus magnification at 100% level available on almost all of today’s mirrorless cameras allows manual focus to be done with flawless precision.
- Insane fps. Sport or wildlife shooters will love these cameras. There’s no mirror flapping around inside camera so their shooting speed is limited only by sensor readout and processor/memory card sped.
- Cheaper and easier to produce, less chance for malfunction. There are far less moving parts in mirrorless cameras, and less need for mechanical precision. (no pentaprism or complex mirror assembly)
- Silent operation. No mirror slap to scare the birds away. Still, there is mechanical shutter sound, but this will change soon. Some cameras like latest Sony NEX models already have electronic first curtain shutter and I am sure real electronic shutters are just around the corner. (Read more on Sony NEX-F3 here).
- Legacy lenses usage. Short flange-to-back distance allows easy use of old manual lenses, some of which actually feature really high-end optics, and others can be bought next to nothing on e-bay.
- No mirror induced shake. Long exposure tripod users will love this one. Many DSLR cameras have an option to raise mirror a few seconds before the real exposure starts, just to eliminate any possible shake. There are no such problems with mirrorless cameras.
- Battery life. Mirrorless cameras work in live-view mode only; electronics and sensor can drain the battery very fast. This will probably be avoided in future with stronger batteries or lower consumption electronics.
- Not enough native lenses. Well, at this time mirrorless systems are still rather new and there is a lack of various lenses. As the time passes, this will also become irrelevant as every manufacturer adds two or three lenses per year to their lineup. Panasonic and Olympus have allready more than 30 lenses for their micro four-thirds system.
- Focus tracking not as good as phase detection systems on DSLRS. Sport of wildlife shooters might like insane fps on some modern mirrorless cameras, but there is still no contrast detection system that can keep up with focus tracking in high end pro DLSRS like Nikon D4 or Canon 1DX.
- EVF technology still has to mature. As good as it is, it’s still inferior to OVF due to limits of resolution and refresh rate. I believe this is also just a temporary case; better EVF modules are around the corner.
- Small body is not fit for large telephoto lenses and can be fiddly for use. Almost all mirrorless cameras today are small. As much as many like it, it is a problem when used with larger telephoto lenses. Sensor size dictates big optics, especially for larger apertures and longer focal distances. Still, I don’t see a reason why the camera can’t be made bigger just for the size of it, the new Panasonic GH3 being an obvious example.
You have probably noticed that all of CONS are just a limitation of current technology development, and will be surpassed one by one with each new mirrorless generation.
In my opinion, mirrorless will become primary camera choice in around three or four years. Many professionals have already bought into mirrorless, and more will come. Why would they bother lugging behemoths like Canon single digit series or Nikon D800 and D4, when Olympus OM-D or Sony NEX-7 deliver fantastic image quality at a fraction of the weight and size. I speculate even full-frame mirrorless are soon upon us. Full-frame sensor will still dictate large optics, but not everyone uses huge tele-lenses so there’s no real need for a huge camera…
There is also the case of Sony SLT technology I feel it should be addressed to. In my opinion, it is just a temporary link between SLR and mirrorless cameras. Only reason for its existence is phase AF detection and its speed and tracking abilities. I any other aspect SLT cameras behave like true mirrorless, and will probably disappear as technology progresses in the next few years.
Now, the interesting parts of the whole story are current manufacturer’s strategies. Sony, Olympus (with Panasonic) and Fuji have invested a lot into theirs mirrorless systems. All of them have advanced level cameras, as well as a growing range of lenses. On the other side, two of the biggest players in photo industry – Canon and Nikon don’t seem to acknowledge mirrorless as a serious contender. Nikon 1 and the recent Canon EOS-M systems are in the eyes of photo-community only toys with exchangeable lenses. They are clearly made purely for amateur users, have a limited ergonomics and just several “soccer-mom” lenses. It is obvious that Canon and Nikon do not want to hurt their DSLR sales, but it’s a strategy that might rebound right into their faces.
My long-term prediction is that at some point, mirror will be simply dropped out. Due to lens compatibility, lens mount and flange-to-back distance would stay the same, but instead of mirror, future Canons and Nikons will have empty space and electronic viewfinder instead of optical one. We might still be a few years from complete market domination, but the path is clear. After almost a century of SLR shooting, the time for a new approach is finally here.
DSLR camera will not disappear though; there will always be demand for them, just like for analog film. SLR’s will simply be used by users who have a clear desire or reason to use them, and mass market will make a shift towards mirrorless.