Den Lenni from Fstopacademy posted the very frist A7s low light video test (scroll at the bottom of his site to fund the video).
The image on very top shows you the quality at ISO 409,600. But before to cry about the grain and nosie you see you have to check the same scene at ISO 6,400:
As you see there is no light at all in the room! So it's quite a miracle that you actually CAN SEE something at ISO 409,600!
And up to ISO 102,400 the noise isn't really bad at all:
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