Thought you A7S users might be interested in this. Hopper Stone, who is the set photographer for the Ghostbusters reboot currently shooting in Boston, uses A7S bodies predominantly with the Sony lenses--first officially released still:

Paul Feig debuts first official look at the Ghostbusters cast | EW.com (http://www.ew.com/article/2015/07/10/ghostbusters-official-cast-photo)

That's very interesting. Is it because of the video feature of the A7S primarily? I would think if he was mostly stills, that the A7R would be more appealing?

I can venture a guess as to a couple of reasons for using the A7s for set stills:

Silent picture taking. You can turn off that annoying 'mirror/shutter click' sound, and thereby not need to use an awkwardly unwieldy blimp housing for the camera. (I've shot stills in the middle of an orchestra recording with the A7s camera functioning completely silently.)

Speed. We all think of most still cameras as being fast, but if there's movement you're trying to freeze it may call for a shutter speed of 1/250th of a second or faster. Think about what that does to the ISO you may need. There are some pretty dark sets out there -- let's say the DP is rating the movie's cameras at 1000 ISO - and shooting wide open at t/1.4 - with a shutter speed of 1/48th of a second. A still photog with a good f/2.8 zoom is starting out two stops behind in exposure, then another 2+ stops to get to a shutter speed of 250 to stop motion blur. Now we're past 4 stops of difference, so you're already talking an ISO of 16,000 to get the same basic exposure for your stills as the movie is getting! Now think about doing any kind of stills in the 'dark' areas of the set...

Dave, I believe you are correct on both counts. I had lunch with Hopper last year and I recall him bringing up both of those points.