Brandon Li, in the BTS (9:00) of the “Crossroads” video he made for Sony, says there’s noise even at relatively low ISOs. Could it be that Sony is just using less aggressive processing than in their other less video-centric alpha cameras? Not a few filmmakers complained in the past of not being able to lessen the amount of in-camera noise reduction, preferring instead to deal with it in post. Or is there simply no escaping the fact that oversampled 4K has finer noise? Or is it because his footage is underexposed? 🙂 The text below is taken from the transcript of the video.
The a7s III is not noise free. There is noise in the image even at relatively low ISOs. And you’re still going to see this noise even if you use S-log 3. I believe you get the same level of noise from the sensor regardless of your picture profile so I don’t know exactly what’s causing this noise but I found that as long as the subject of your scene is not in the shadows then you can go to super high ISOs and it will still look great.
But if your subject is in the shadows it’s in the toe of that exposure curve you will have noise issues when you try to raise things up in post, so what I did in post was I added a luminance mask to my noise reduction so that it only reduced noise in the shadows of the image and I applied the noise reduction at the minimum amount to make the noise bearable to my eyes and the image ended up coming out looking very clean.
At the same time, this chap downloaded some sample footage from James Matthews’ channel and says it looks super clean:
[Edit 01.09.2020] The saga continues. Josh Yeo just uploaded a video in which he says:
So I will say in color grading this I did notice that there is some definite noise going on. I don’t want to say that there’s more noise than in the a7 III but the noise is larger and I think it’s just because the a7 III is a downsampled 6K image to 4K and so there’s you know it there’s a little bit of cleanup that’s going on when you have that process happening. Most of the profiles look like there’s a little bit of sharpening going on and we can see that in the noise and just what the style of noise is like. This is like a stupid little tiny problem to have. It’s like someone who could taste the difference between a $250 bottle of wine and a $2,500 bottle of wine would probably notice this. Most people are not going to see this noise at all and in fact it cleans up quite nicely when you open DaVinci Resolve and you add de-noise, it takes care of it.
The Daejeon Chronicles 
This video is awesome but to much compressed, some others are less compressed (yours for example).
It’s weird to upload such in a “bad” quality (the 3840p parameter doesn’t help) to show the qualities of a new product.
Anyway, he certainly knows what he did ^^
YouTube compression certainly isn’t doing it any favors. That’s just one more reason I’m really an advocate of HDR. First, the color, contrast, dynamic range and amount of apparent detail would improve dramatically. And YouTube’s HDR is much higher quality than ordinary 4K. From Brandon’s examples of S-log footage, it looks like he’s really underexposing a lot, which isn’t doing any favors as far as noise levels go. In the clip of the wall with the doorway in the distance, he could easily have given a couple of stops more exposure and recovered detail in the highlights. I could do that even with 8-bit S-log2.
Yes, also. The famous ETTR.
The thing with HDR is that you need such a screen to enjoy it.
If you have a casual screen (calibrated but still not 10 bits, etc), the image is kind of washed.