"....More bit depth does not in itself produce a wider dynamic range. Cutting the pie into more pieces does not make the pie bigger....."
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YOU HAVE HIT THE NAIL RIGHT ON IT'S GLARING HEAD !!!!!
It's almost all about PHOTOSITE SIZE IN MICRONS!!!
The Canon 1DxMk2 is about 6.3 or 6.4 microns so it's image quality in terms of noise and low light capability is going to be pretty darn good! The Sony A7s2 has about an 11 to 12 micron photosite size, so IT'S low light ability is and DOES BLOW AWAY the 1DxMk2's! Now what SHOULD BE DONE in the camera industry, is that that manufacturers need to start getting into Medium Format sensor sizes STARTING at 56mm by 42mm at a MINIMUM of 30 megapixels (13.9 microns per photosite) up to 50 megapixels (6.8 microns per photosite) so you KEEP the high end low-light gathering power of the Canon 1DxMk1 and Sony A7s2 BUT get the increased resolution we so very much want these days. Lenses would be easier AND CHEAPER to manufacture AND we would get that beautiful Bokeh inherent to large image sensors!
IDEALLY, we should be moving into aspect ratio agnostic 70mm by 55mm sensors at 8192 by 6144 pixel image size (50.3 megapixels) which would give us an 8.5 micron photosite size which is probably what 99.9997 percent of us will find perfect-enough for BOTH day and night photography! That 70mm x 55mm and 4:3 aspect ratio can be cropped on just the vertical axis to ANY other aspect ratio we need for stills (3:2 and 4:3) and video (16:9 broadcast video or Cinema DCI 1.89:1). With that 50 megapixel we can EASILY use it for almost any stills and video purpose we want with enough LOW-NOISE and HIGH-END LIGHT GATHERING POWER that our imagery will be good for DECADES to come!
Soooooo, Canon, Sony, Nikon, Fuji, Panasonic, Leica, Hasselblad, Phase One, etc how about getting 70mm by 55mm sensors at 8092 x 6144 pixels (4:3) onto YOUR cameras !!!!!
BRING IT ON BAAAAAABBEEEEEEEE !!!!!