A7Rii: Black levels shift/crush only in video?

[rytron]

Wondering if anyone has any insight into this. Copious google and DVXuser searching hasn't helped thus far.

I'm noticing that, regardless of colour profile settings, when I start recording video on the A7Rii that my histogram shows that the black levels are shifting to the right. I've attached a picture to this note showing the histogram shift. The camera had the lens cap on, and was in manual mode (though this happens when I rotate the slider into video mode as well, the effect is obvious in a stills mode as I can see the histogram showing the absolute blacks before I hit record and shifting immediately after beginning a recording).

 

What could be causing this shift only when video recording starts? Incidentally, if I rotate the camera dial into video-only mode, then the histogram still shifts to the right, even when not recording. It's like the camera is saying "nope, you can't record absolute blacks in video mode, sorry."

 

I've got 7 profiles set up, one for each of the four cinetone curves, one for rec 709, one for rec 709 800%, and one for SLOG2. The black shift in video happens on all of the, as well as the "No Profile" setting. I've futzed with black levels and slopes/knee and it's not making any difference.

 

Any thoughts? Still loving the video quality, but wondering if I've got something setup horribly wrong. I tried resetting a colour profile to its factory setting and saw the same results in the histogram.

 

(the gaff tape on the cam is just for debranding, nothing smashed on it)

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