EVFs always have a lag. The very best lag I’ve seen in one is the one in the Samsung NX1, which runs at about 1/250 behind reality. Samsung did something that is mostly done in the video system: they “genlocked” the EVF to the image sensor. I won’t get into the technical details of what that means, but in essence the signal is about as direct as you can get from sensor to EVF.

The problem is that to make that 1/250 lag faster you need to run the sensor faster. Which means more technology in and around the sensor, and the sensor will probably run hotter, too. Samsung and a few others are running EVFs at about the max speed you can with current technologies. The good news is that will change with time as new abilities and technologies emerge. But it will change somewhat slowly, I think.

And that 1/250 lag is lag. That 1/250 visual lag sits on top of your recognition lag (response to the scene in front of you) which sits on top of the shutter lag. So you get lag+lag+lag = real lag. I don’t want lag. Indeed, I have to make sure that I’m on top of my game and my brain is processing fast when I’m shooting a number of subjects. I mostly choose cameras—such as the Nikon D5 or the D500—that have minimal shutter lags and no viewfinder lag.

But the initial EVF lag isn’t the only lag in the mirrorless systems. In DSLRs we talk about “viewfinder blackout,” which is the time that the viewfinder is dark while the mirror is flipped up. The D5 has an incredibly short viewfinder blackout, meaning that when I’m panning with action there is very little time I’m not looking at my subject in real time. The D500 is also quite good at this.

With mirrorless systems, some have this funny “slide show” kind of effect when you’re shooting continuously. The latest Fujifilm’s and Sony’s have minimized this, but they also need time to clear the sensor data before turning it back on. So there’s still a bit of disjointedness to what you’re watching. And again, if you keep running mirrorless systems continuously, you’re building heat at the sensor. I’d prefer to keep that to a minimum when I’m shooting in low light.

It is such fun mix of wrong statements, wrong assumptions, and specially not providing enough data.

What happens with DSLR?

Before camera can take a picture you have nervous system reaction (processing and command to your finger), delay from shutter moment press to start of actual shooting routine, time required to focusing, time required to lift up mirror, usually at same time we have some LSI and sensor setup procedures. Most fun thing is that even simplest reaction time is around 130ms, more complex visual one can be significantly higher. All other lags can be found in good technical reviews and all of them are significantly smaller compared to nervous system performance and focusing performance.

How good sport and nature shooters make their good shots? They either use serial shooting or they are good at prediction, both means what they press shutter ahead of time, well ahead.

With mirrorless camera you do not have any mirror, so time is saved. Most probably NX1 viewfinder lag is not 1/250 (it must be sensor readout speed), but closer to double of this. Research in virtual reality headsets requires similar lag for experience to be felt real. So, nothing wrong with it. It is very small. Btw, term genlocked is fully incorrect and must not be used here.

Viewfinder blackout has nothing to do with mirrorless native shortcoming, but more with omission in firmware and some hardware design in such sequential shooting mode, made right actual measurable time to return to live picture can be made smaller compared to any DSLR. Good mirrorless natively can shoot at higher fps compared to DSLRs exactly due to mirror.

Good EVF is cheaper compared to good OVF, brighter, can show you picture you will get, can show you focus peaking and enlargement, and lots of different configurable info.