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Sony NXCAM NEX-FS700 CineAlta
4K EXMOR sensor with SDI, slow-motion recording.

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Old January 14th, 2015, 04:26 AM   #1
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Join Date: Oct 2012
Location: London, United Kingdom
Posts: 45
FS700 4K Raw low light 'bug' or 'feature'?

Coming back from a shoot when we were chasing the light the editor called in with a slightly odd problem with the footage: Shooting 4K Raw and (very!) underexposed the colour temperature of the RAW footage suddenly changed.

Note: The metadata didn't change, rather it seems the gain levels of the three channels suddenly jumped (Red and Blue dropped a bit and the green jumped).

I've been investigating this further in the office today. The issue was not due to me being a muppet and having auto white balance flipped or changing WB mid way through shot (although that was a reasonable assumption). Nor is the issue in the Odyssey as I can see it on the camera monitor as well.

Notably it occurs in all 4K settings (24p, 30p, 60p, 25-, 50p) except 120fps burst. It also doesn't happen in 2K Raw in any frame rate (24,25,30,50,60+).

Also, notably, it is unaffected by black gamma settings (as you might expect given it's Raw) and running a black balance also doesn't help.

As far as I can tell the 'bug' is a 'feature' of the camera*. It only happens when the the frame is significantly filled with an underexposed (and therefore very noisy) image (i.e. if there is a large enough patch of . To me it looks like the camera is adjusting the gain settings (reducing red and blue, increasing green) to reduce the noise and make itself more 'sensitive' in dark areas.

The issue with my shot was that we had a section of sky in the frame at one point, then we dip to lose it. After the dip, the image suddenly.

If anyone of you fine gentlemen (and ladies) could find the time to have a go to check if it happens with yours that would be ace as I'd like to see if it is just mine. It's pretty easy to do: Set your camera to 4K Raw - and close down the lens (or flip in the ND) so you can jump between a 'normal' exposure and one severely underexpose. You should see underexposed image suddenly become a little green.

*I was hoping to speak to someone at Sony Prime Support to try and confirm it is a feature not a bug (or my camera being damaged!, but they're answer machine is telling me the office is closed - despite the fact the recorded message also says it should be open: glad I don't have a major issue then!
DoP, London, UK
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