I’m not saying they are bad or useless. They just don’t make any sense yet. Here’s why …
The biggest, if not the only, reason for going mirrorless is size reduction. Everything else, good or bad, about mirrorless are just consequences of size reduction.
Let’s talk about the good stuff first.
Although a lot of DSLR shooters hate electronic viewfinders (EVF) they are actually very useful tools. EVFs allow you to see what’s hitting the sensor before you hit the shutter button and that is a very good thing. No more chimping after every shot. You also get a horizon level indicator, histogram, focus peaking and automatic brightness boost among other goodies. I like EVFs. In fact, I feel that I have become a slave of EVF. When I shoot with my DSLR I always have to double check if my camera is giving me the correct exposure values. Not so with EVFs. What I see is what I get. EVFs are a necessary “evil” for going mirrorless. There’s no other way around it unless you want to have a rangefinder like the Leica.
Lens adaptability is another good consequence of going mirrorless. By getting rid of the mirror, lenses can now be mounted much closer to the sensor thus resulting in smaller lenses. It also means that with a cheap adapter, you could mount just about any full frame lens regardless of brand. Of course this also means that camera bodies can be made thinner and lighter. That’s size reduction in action.
Without the flapping mirror, the camera is quieter. This is essential when you are into wildlife photography or when you need to be discrete during weddings or funerals or even when out in the streets.
Now on to the disadvantages of going mirrorless.
Mediocre battery life is first on my list. The EVF and the sensor, among other electronics, need to be running all the time otherwise you can’t see anything. This reduces battery life considerably. And since the camera body is much smaller, batteries also need to be smaller which doesn’t really help with the problem.
EVFs aren’t there yet in terms of speed. When you are shooting sports, the lag can be irritating and/or disastrous.
Ask a DSLR fanboi and he can tell you more about why going mirrorless is bad.
Bottomline is that you probably do not want to go mirrorless for its disadvantages but every advantage you get are just direct consequences of size reduction. To reduce the size of camera bodies they needed to remove the mirror and use an EVF. To reduce the size of the body and lenses they needed to bring the lens mount closer to the sensor. Size reduction is the whole point of going mirrorless.
So with all the pros and cons aside, why am I saying that full frame mirrorless cameras do not make any sense yet? Because they are still HUGE! Yes, the cameras are smaller but the large sensor requires large lenses which defeats the purpose of going smaller. You are better off buying a full frame DSLR instead because the size difference isn’t really that much and with a DSLR you get a more ergonomic grip that helps carry those hernia-inducing heavy lenses.
So when is full frame mirrorless going to make sense? When manufacturers stop upgrading their DSLRs and you have no other option but to buy mirrorless. This is a big marketing problem especially for the giants like Nikon and Canon. I can see Sony heading in that direction. When was the last time Sony upgaded a DSLR? It’s very risky but this is exactly what Olympus did. They totally stopped upgrading their DSLRs, went mirrorless and never looked back. Yes, they lost loyal customers but in return they gained new converts because mirrorless m43 makes total sense. They are small.
Again, full frame mirrorless do not make any sense. Get a full frame DSLR instead. If you really want to go small, buy m43 or APS-C mirrorless cameras. My personal recommendation would be the m43 format because the mount is standard which means you have more lens choices. And did I say they are small? That’s the whole point of going mirrorless — size reduction.