Sony A7s 5 stops brighter than NEX-5R??
I do video work in the Outdoor industry, mainly a combination of video and timelapses which I always shoot as raw image sequences. I'm considering upgrading from the NEX-5R to the A7s because of the increased low light for video (in outdoor filming, low light is the norm rather than the exception). Let me know if I am understanding this right...
-According to DXOMark, the A7s has a usable ISO of 3702, whereas the NEX-5R has a usable rating of 910. This matches my previous experience that anything above ISO 800 looks a little too grainy. That's over 2 stops just from difference in sensitivity.
Yes, and (almost) one stop more than the A7 has.
-According to Digicamdb, the A7s pixel area is 69.22 um^2 vs the 22.66um^2 of the NEX-5R. That's over a 3x difference in area. Does that also equate to a 3 stop increase in light gathering ability? Meaning that combined with the increased ISO sensitivity, I could expect roughly 5 stops of extra light gathering with the A7s and potentially use my f4 zoom lens at decent shutter speed when I would have had to switch to a f/1.4 prime in the past and slowed the shutter?
That is already accounted for in the DxOMark number.
DxO gives you the equivalent of 2 stops for 'low' or 'usuable' ISO.
When you go to high ISO, this factor increases for the A7s - check the graphs that DxO put up, as you see the dramatic improvement at higher ISO - and the A7s performs around 2 to 3 stops better than the A7! But we are talking ISO way past 6400.
At ISO 25,000, the A7s is more than 4 stops past the 5R... but even the A7s images will become grainy (however they do maintain the full-frame look).