So I've done a bunch of tests under differently lighting conditions, sunlight, shadow-- shadow to sunlight. Day, night. With various ND filters (.03-1.2) and have determined that the native ISO of this camera is ISO 640. Any thoughts, comments?
In my completely unscientific test (and use) of the camera 640 seems plausible. I've had a hard time telling the difference between 320, 640, and 1250. Those seem to be the cleanest signals. I doubt Canon would set the base ISO at 1250 (though the C300 is 850 so.....?) which leaves me leaning towards 320 or 640.
It'd be nice to know. Here's a video that lays out all the ISO's side-by-side for a comparison on the 5D3 -