Now, the show time of the Sony CMOS sensor - dynamic range under long exposure!
First of all, it was lucky that I bracketed a bit for the long exposure shots so I have had just the right parameters for analysis!
Indeed, when Phase One wraps up the ISO settings (along with the dedicated long exposure mode for the IQ380 and IQ260) things can get very confusing - what is the real native ISO?
Instead of starting another long debate here, I employ a simpler method to try to minimize dispute:
I shoot each back at the lowest possible ISO (where for the IQ380 it is ISO 200 in the dedicated long exposure mode). I use the Lee Big Stopper. I shoot at the same aperture.
What I have found is that regardless of the difference of ISO among these three backs, indeed the same exposure time gave me about the same highlight headroom! See proof below: I converted all RAW files by Capture One v9.0.2 then checked the mean value of the fixed sky region. These are about the same.
Then I used the following settings for each image: I match the exposure of each image, then use the "Pick white balance tool" on the same spot, then push +100 shadow and pull +100 highlight, then disable noise reduction.
Note that for these two CMOS backs when I took the long exposure shot I disabled darkframe noise reduction by setting "Camera Mode" to "Aerial". This is indeed a key feature for landscape photography so to avoid waiting for the noise reduction countdown! Then for these three backs I moved the slider of "Single Pixel" to 1 (out of 100).
Now we look into the shadow: boom! You know what I'm talking about and why I am a fan of the Sony CMOS sensor! It is really the king in this kind of shootings! This is what I am willing to sacrifice other things for.