I shot a branded doc in Nantucket over the summer about kite boarding/surfing with my new Sony FX9 and when I got to the color correction, I noticed that so much of the footage was incorrectly balanced, almost always too green. As a perfectionist, I always want to get the best image out of the camera from the get go, so this inconsistency led me to see if it was the camera or if it was my fault, perhaps a lack of understanding or misinterpretation of levels that was causing me to miss the mark.
So, the first thing I did was see if anyone else had written something about this on the net, or if Sony themselves knew of the issue. There was almost nothing on the subject except for legend, Alister Chapman's article on the subject.
Notice how green the boat is, in the "FROM CAMERA" still.
Above, you'll see the results of setting white balance (WB) in camera. "+Tint" refers to how much magenta is being added. The picture on the far left is when auto balancing to a white piece of paper and letting the camera decide what the correct WB settings should be. According to Alister Chapman's article, Sony is somewhat aware of the problem and recommends shooting 5000k +20 Tint when in daylight. Which do you think looks best or most accurate?
I would probably say the 5500k with +20 Tint looks most accurate. You'll notice the 5000k is too blue since the actual temp in the room is probably closer to 6000k due to the indirect daylight; so this isn't a concern and shouldn't really be factored as a flaw in this test. However, we are at least seeing less of a green shift at that level. Overall, the issue seems clear, the higher the color temperature, the more the camera skews green.
Now, the above photo is me having color corrected everything and the changes I had to make to get something that looked good to my eye and the scopes. They all look fairly decent, so even if you were operating as if the camera was balancing correctly on its own, you could still get to a good image after color correction. However, if you are passing the footage off to someone else and unsure how they'll use the footage, or if you're shooting live, or if you just want to nail the levels for your own pride as a cinematographer, then you should be adjusting the tint toward magenta as you increase kelvin above 5000k (and I didn't test lower, but probably starting at 4300k).
CONCLUSION
The Sony FX9 sensor skews green as you exceed 4300k. Start with +20 at 5000k and probably +30 at 6000k with increments in between. I haven't noticed issues at 3200k, but if I do, I'll do a test, or if you do, let me know!
What's also interesting is if you watch the whole video, is how when using the auto white balance color correction in Premiere's Lumetri, the setting that requires the least adjustment is the Sony WB Set (far left image). That seems to indicate that AI seems to think these green skewed images are correct!
Wow, you made it this far! You must actually be interested in this stuff! We should be friends! Feel free to check out the full video test below.
And so long COVID-bun. I went back to short hair. It was worth a shot :)