Slog A7iii

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Kanisha Dezarn

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Aug 3, 2024, 4:55:00 PM8/3/24

to kingpersvitli

As a filmmaker who was brought up in the photo chemical world I never choose to use an AUTO ISO mode, but I am clearly missing something here? When I go to change the ISO on the camera the dialog says it is not possible in Gamma: S-Log2 mode?

I've only used the A7RII in sLog. If I recall, on this model the ISO minimum is 800 and can not be set lower than that. It might even have been fixed at 800, but I can't remember. It was not "auto ISO". On the A7III it might have a minimum setting of ISO 1600.

My experience was that in camera recording in sLog did not make good images, with substantial compression blocks in the darker parts of the image. Recording to ProRes on an external recorder solved this issue, even though the recording was still only 8 bits over the HDMI.

Hi Bruce, Henry Cline here. The thing I cannot understand is that while in s-Log the ISO in the viewfinder just says AUTO ISO cant change the ISO because an error message comes up that says unable due to Gamma S-Log configuration. So, I am just trying to understand better what exactly it is set at? Confusing for sure. I greatly appreciate your input and hope you are well.

Most websites say it is 800 ISO on a Sony A7iii in S-Log video. Should be a way to confirm that by pointing the camera at a grey scale or something and taking a meter reading at 800 ISO and seeing how it looks.

Yes 800 ISO for log in the A7III.. As with Sony video cameras.. Sony's idea is that its best to shoot SLOG at a fixed "native" ISO (like you would with film) thats gives the best balance over/under grey level.. according to Sony engineers.. the lowest ISO you can set is 800 in PP7 or 8.. slog2/3.. but you can set higher.. you are in Auto ISO mode if thats what you are seeing on the screen..go into the ISO setting and just scroll out of auto..

But the A7RIII and the A7III also have HLG (Hyper Log Gamma) curves..1/2/3 PP10.. designed for HDR TV,s.. some people as using them as a sort of half way house.. between standard curves and Slog.. problem with Slog in these cameras is the 8 bit recording.. in theory it mathematically can't even be done.. sort of contradictory terms.. slog2 is apparently a little better in its data distribution..

Excuse my ignorance, but I have looked thru every menu and dont see a video mode to set to manual, my exposure mode is set yo manual, but I cannot find the "video" mode you mention. Thanks very much for the advice.

apologies ..I have the camera in front ion me now.. yes sorry meant the exposure mode.. does your screen still say you are in ISO Auto mode.. ?.. your top dial is set to the little film frame Icon.. I just set my camera to PP7.. I can set 800 ISO minimum and 102,400 max.. can you get out of Auto ISO in non log PP,s..

As 800 is the minimum ISO for Slog.. go into another PP.. set ISO for 800 or over.. then go back to PP7 .. are you still stuck in Auto ISO in all PP.. if exposure manual then somethings wrong there.. try all rest.. if still happens I would take it back on warranty ..

ok good.. I just bought the A7III last year as a B camera and to use with a Ronin S.. so had to study up on the damn thing too.. its a nice camera.. one of the main things being the larger A9 type batteries ..

When you zoom in, you can see differences in noise:At ISO 8,000, the SLog-3 shot is so noisy that it's unusable. When we increase the ISO to 20,000, it's still noisier than the PP Off shot, but just barely. Even though it's clearly noisier when zoomed in on a still frame, the difference in noise isn't apparent when you playback the clips as video.

Then at ISO 64,000, the noise is just as low as the PP Off image, but at ISO 64,000, the image has been overexposed to the point that it looks slightly washed out in terms of contrast. Also, a subjective critique, but I think the colors look worse in the ISO 64,000 image. A point where I notice both these things (muted color and low contrast) is the part of the road illuminated by the headlights

To answer your question, for me, I shoot in slog3 because it's an essential part of my workflow. It allows me to add a blanket lut and grade across an entire project and I really like it. I love the image. Of course, noise has been a hot topic for a long time. My consensus from your tests and the fact that most of the industry captures Log no matter the scene is that we're not punching in 200% to gauge noise levels while viewing a film and a certain amount of noise is acceptable. For really important work where this conversation comes up in pre-production and healthy noise levels are important, I think being intentional about how you rate your camera at one of it's two base ISO's is what is really important.

Not to take anything away from your testing, but any high-end production that is shooting LOG will surely be grading in Resolve Studio, or Baselight, or some other full-featured grading program where adding the necessary amount of noise reduction in post is simple and effective. Of course, if someone is only using the free version of Resolve then I think NR is one of the features not available. My advice is to upgrade. Resolve was a $500K program a few years ago that couldn't do 1/10th of what it can do today. $300 is a bargain.

On my F55, I only ever shoot S-LOG, RAW, or X-OCN and I pretty add a touch of NR on the final node of EVERY grade. It does help, even with "normal" footage where you probably wouldn't even think noise was an issue. On my FX6, FS7, and A1, I only add a little NR to S-LOG when I think it is necessary.

I think there is a bit of a common miss-conception about grading flexibility with different gammas. S-Log doesn't have any greater grading flexibility than any other gamma. However so many of the commonly used tools such as LUT's or other plugins found in most edit applications evolved as simply ways to grade log footage within the constraints of a 709 workflow so many have gained the impression that Log has more flexibility. In reality if you take log, 709 or any other gamma into a decent post production workflow such as a proper colour managed workflow like ACES and you eliminate the gamma by transforming it into a linear space then there is no difference in the grading flexibility, all will grade equally well as in essence all contain the very same image information.

Gamma curves are simply a mathematical calculation applied to the original material to make it fit in a limited recording range. They do not make an image more or less gradable and being a simple mathematical calculation they can be reversed to remove the gamma.

What S-Log does allow for is a greater dynamic range and a larger DR might be important for many shots, but this isn't always the case. This greater range is achieved by squashing the original material using log math and this allows more stops to be stored in the same size data bucket. But, that comes at a price. S-Log3 and 14+ stops recorded into code values 95-886 means each stop on average has 56 code values (you actually have more for brighter stops but less for stops below middle grey). If you use vanilla Rec-709, with no knee (not S-Cinetone or any of the other modified versions of 709) then you will have 6 stops in code values 64 to 1023 so on average each stop will have 159 code values, almost 3 times as many as log. I'm quite sure that most reading this will already be aware of the advantages that more code values per stop brings, after all it's why we prefer 10 bit over 8 bit recordings. The difference in code values per stop between S-Log3 and vanilla Rec-709 is not that different to the difference between an 8 bit and a 10 bit recording.

However in a considerably under exposed situation where neither the log or the 709 can be fully exposed it isn't going to make a huge difference what gamma you use because the limiting factor is the actual sensitivity of the sensor and the noise it produces. To go from a certain scene brightness to a like for like final screen brightness the cumulative gain used (sensor gain + gamma gain + post gain) will be the same whatever gamma you use, so the ratio of signal to noise will be broadly the same whatever route you take and it's the noise that will likely limit how well you can grade or manipulate the material rather than the gamma choice.

But if your gamma choice allows you to fill your recording range rather than only using a small part of it then you will have more code values per stop with a narrow range gamma than a wide range one and that will provide more textures and that will grade better in just the same way as a 10 bit recording with 970 code values will grade better than an 8 bit recording with 235 values. So for some studio applications where you have control over your lighting there can be advantages for using 709.