How does one activate the electronic shutter of the Sony a7r2? Google seems to indicate that I put it in silent shooting mode.
I have an A7R2. Sony's documentation is a little confusing on this issue. (OK, on all issues.)
You should know that the "electronic" shutter is always used. All that means is that the sensor is kind of "refreshed" and put in a state that is ready to accept and read a new, fresh image. The sensor does not simply record what it has been sending to the viewfinder while you were framing the shot. It kind of "starts fresh" each time it captures an image, to avoid artifacts due to what the sensor was "seeing" just before.
Normally, the time that the sensor will be exposed to light is controlled by the mechanical shutter. The mechanical shutter closes (because it is normally open so you can frame the shot), then that refresh occurs, then the front curtain opens. When you use only the "electronic" shutter, it can start recording that image just a tiny bit sooner. It then recalculates when to stop capturing the image based on the fact that it started capturing the image sooner.
Go to the "Custom Settings" tab (the gear icon), Page 5, "Silent Shooting." That mode turns off the mechanical shutter and only uses the "electronic" shutter. Note that this turns off both the "front" and "rear" "curtains" of the shutter. (see any standard explanation as to how shutters work)
There are some caveats to using this mode. The worst, for me, is that it forces the camera to store the files as 12-bit images instead of 14-bit. Another problem is that the electronic shutter may work faster than the other parts of the camera that are still mechanical. Namely, the aperture blades. They have to have time to close to the right setting before the image is taken, but the electronic shutter may start capturing the image before the aperture blades have had a chance to settle into place, causing weird artifacts in your image. This can be partially avoided if you use a wider aperture. Also, Sony says that this may cause other problems with non-Sony lenses. Yes, Sony could have designed the camera to wait till the aperture blades are in position, but then that would defeat the purpose of being able to start the image capture that tiny bit sooner.
The other, related setting is the "e-Front-Curtain Shutter," on the same page in the menus. This only turns off the "front" curtain of the shutter, but the "rear" curtain still closes at the end of the exposure. It is supposedly designed to provide a shorter delay between pressing the shutter release and the instant the image is actually taken. However, turning this part off is what causes all the problems listed above. So, for me, they aren't really worth it. The camera will still make some sound anyway, because the aperture still needs to close to the correct setting, and some auto-focus motors still make sounds.