There is a lot of chat online about the advantages of DSLRs vs mirrorless cameras. There is no doubt that DSLRs still have a few advantages. But there is absolutely no doubt in my mind that the DSLRs and their mirrors’ days are counted. Why? Simply put mirrors are a big, awkward, fragile mechanical holdover from the film days and they have no future in a digital world. Mirrors are to digital cameras what carburetors are to modern cars. Complex, fiddly, fragile, limiting and outdated. Some people still like carburetors because they can be fiddled with, but Electronically-controlled Fuel Injection is far superior in nearly every way.
Look at the diagram above and compare the complexity and bulk of the DSLR on the left with the simplicity and compactness of the mirrorless on the right. Notice that the use of the main mirror creates the need to also add the prism and the auto-exposure sensor above, as well as a secondary mirror and auto-focus sensor on the bottom. Then take a look at the video below and watch how the main mirror and secondary mirror must quickly and violently swing up and out of the way and then back down. Watch how they bounce around in the process. Imagine doing that 10 times per second.
It is an amazing feat of engineering from the likes of Canon and Nikon to have perfected this complex mechanism to achieve fast shooting speeds, high reliability and all this while keeping noise and vibrations to a minimum. However, as with all things mechanical there are physical limits that will never be surpassed and they are pretty much there already.
Now let’s look at the pros and cons. Up until now DSLRs are still the way to go if you need the best ability to track fast moving subjects. This is because of the way the Phase-Detect AF sensors below the secondary mirror works. The other advantage is that mirrors allow for big and bright optical viewfinders. Finally, because DSLRs need to be much thicker to make room for the mirror, they have room for larger batteries. These larger batteries combined with the lack of electronic viewfinder and the fact that the sensor does not need to be powered all the time makes for fantastic battery life.
I contend that these advantages, except for battery life, will basically disappear or even become weaknesses in the near future. Let’s take the auto-focus for example. DSLRs actually suffer from focussing inaccuracies like back or front-focussing. This is a problem caused by mechanical variances in the AF system and the lenses which often cause some lenses to consistently focus a little bit in front or behind the subject. In the past this has required you to send your lens and camera to the shop for adjustments. More recently camera makers have included facilities to register and fine-tune your lenses’ focussing offset with your camera’s electronics. Nikon went to great lengths to introduce a built-in system that automates this process on it’s latest flagships, the D5 and D500. On the other hand, mirrorless cameras focus directly on the sensor so when the camera achieves focus, you know it will be bang on. Also, since mirrorless cameras use the main sensor to focus, they can spread the focusing point over the entire surface of the sensor and they can combine both contrast-detect and phase-detect pixels. When manually focussing with a mirrorless camera, you are seeing the focus as it is exactly on the actual image sensor. The latest crop of mirrorless cameras like the Sony A6300 are getting really close to DSLRs in terms of tracking moving subjects but are actually superior in other areas like single-focus speed and accuracy. Mirrorless cameras also have a few more tricks up their sleeves like advanced face-tracking, colour tracking, focus-peaking, focus-pull (video), etc. I’m sure we will see new focussing innovations on mirrorless cameras in the future as with digital there are no limits.
The second advantage of DSLRs is the big bright optical viewfinders (OVFs). That advantage has now been overcome and I think it will soon become a disadvantage if it isn’t already. Electronic Viewfinders (EVFs) used to be laggy and low resolution and plagued by visual artifacts. However, the latest generation as found on the Olympus E-M1, Lumix GX8 and the Fuji X-T1 show virtually no lag and no artifacts and they have superb resolution. They will only get better from here. Those EVFs have a long list of advantages over OVFs. EVFs allow you to see the picture as it will be taken: reflecting the exact exposure settings with any filters or special effects applied. So for example, if you are shooting in Velvia mode or in B&W mode, you can see a really good approximation of how the picture will look. When doing composites or long-exposures you can see the final image being built right before your eyes. There are many such advanced features and surely we will see many more in the future. Once again, the only limit is the engineer’s imagination.
The last big advantage of DSLRs is the much longer battery life. This one will be difficult to overcome and it comes from two factors. First is that DSLRs quite simply have larger batteries. This will never be overcome without giving up the size and weight advantages of mirrorless cameras. The second reason for the longer battery life of DSLRs is that mirrorless cameras must drive either an EVF or an LCD/OLED panel and they must keep the sensor and processor fully powered to capture and display the image. This will never be completely overcome so DSLRs will always have better battery life. I am however confident that with improvements in battery technology and low-power microelectronics the battery life of mirrorless cameras will only improve and will soon be more than adequate. As it stands today, mirrorless battery life is only an issue for pros that shoot hundreds of pictures per event and do not have the time to stop and change batteries. For most of us we just need to carry a spare battery and we’re all set. In fact, I rarely shoot more than 200 shots in a day so it is rarely an issue for me.
There is no doubt in my mind that within a few years mirrors in digital cameras will go the way of the dodo. Such arcane, complex and delicate mechanical contraptions simply have no place or future in a digital world.