I got RawDigger to work on the NEX-7 files by running it on a different computer, so I have the NEX-7 results now.
The self heating test at ISO 6400 and 1/4 second exposures of blackness shows some slight self heating (look at the dotted green line, which is a straight line fitted to the green data using least-squares error as the fitting criterion), in spite of the fact that the NEX-7 is in live view mode all the time. The line goes opposite to the direction that I would have thought it would.
The standard deviation of the noise (the noise of the noise) over the series:
How noise floor varies with ISO setting:
The uplifted position of the ISO 6400 point is suprising. High ISO noise reduction is turned off. I wonder if there’s some processing at ISO 6400 that can’t be shut down.
The standard deviation of the noise floor:
Again, there’s that funny kink at the right end of the line.
Making a series of exposures (16 per data point) that keep a 200×200 square at the center of the image near zone VI — a count of 4000 in the green channel — as we progress through the ISO setting possibilities:
The kink is evident at high count levels as well.
Subtracting out the half a stop per stop photon noise slope, we get this — the thinner lines are plus and minus two standard deviations, computed from the 16 exposures per point; the solid lines are the mean values:
This shows slight improvements in SNR by advancing the ISO setting over just using the Exposure control in Lightroom or ACR. The ISO 6400 point is strange, and makes me even more suspicious that there’s some in-camera noise reduction that takes place at that ISO setting no matter how you set up the camera.
At Zone III — about 500 counts in the green channel — we see what is turning into a pattern with this camera:
Subtracting out the photon noise slope, we see:
This set of curves shows that, for the shadow SNR, there’s no point in turning up the ISO setting over the native value of 100; you’ll get slightly better results adding Exposure in Lightroom. I would ignore the kink at the end.