I have the A7s in hand, also have a GH4 and 5Diii. I've done some initial testing and should have more show later tomorrow (July 2nd).
I have mixed feelings, but in my limited time playing around with it here are some thoughts:
- Great ISO performance, but the higher ISOs are indeed pretty grainy.
- Incredible Low Light focusing sensitivity. More than anything I have ever tested, but only with native Sony lenses.
- Im already wishing Sony had many more lenses made for it with very wide apertures
- Paired with the Metabones Speedbooster and wide aperture glass, it could be a low light monster, especially for video.
- The Metabones Adapter, (not the speed booster) AF pretty much did not work, at all. I might have a bad copy. I hear it is slower, but is still supposed to work, but I had no such success with it.
I was very impressed with the DR and colors it could see beyond my own eyes, as grainy as it was:http://www.michaelthemaven.com/?postID=3288&sony-a7s-low-light-portrait-test-maxed-out-at-iso-409-600
There will probably be a sweet spot for low light portraits, but I would imagine it is around ISO 25,600.
Ill post the ISO charts later today.