With a camera like the a7S II, the exposure window is pretty narrow (that’s what separates it from a higher-end camera), so nailing exposure takes lots of practice and discipline.
But it’s not hard if you’re willing to put the time and effort into it. Secondly, you also need to either find time to get better at grading, or hire a colorist. If neither of these are possibilities, your results will suffer, and you’re better off shooting in another picture profile.
If you’re committed to getting the best dynamic range and cinematic image quality from the a7S II, then you might want to watch the following videos in the order they are presented. Please take notes and revisit videos if you have to. Give yourself time and be patient. Even if you don’t end up shooting S-Log3, the knowledge is beneficial.
Finally, practice and see how it turns out for you.
Start by watching these videos on how to use a waveform monitor, if you haven’t already:
https://youtu.be/G84SYddGPQs
What is S-Log3?
S-Log3 is a gamma curve that keeps the image flat for grading. Sony claims it has 1300% more dynamic range (15.3 stops of DR).
What the heck does that mean? You’ve probably heard of people using 18% middle grey to expose cameras. In S-Log3, the middle grey is at 41% (41 IRE). The ‘usual’ 90% white level is at 61% (61 IRE). So, guess where 100% white should fall? 1300%. In other words, Sony claims that the a7S II can record about 13 times more data than Rec. 709.
The key word is ‘can’. Theoretically. However, practically, the dynamic range is limited by the gamut and noise characteristics of the sensor. Here’s a graph showing S-Log2 compared to S-Log3:
Here are the important numbers for S-Log3:
- Black point (0%): 3.5 IRE
- Middle grey (18%): 41 IRE
- 90% point: 61 IRE
Very important note: Sony considers 109 IRE to be within the code values, i.e., 1024 = 109 IRE. They use a factor of 0.9 to bring it to the normalized levels, and this is very confusing to those who read the technical paper for the first (or hundredth) time.
Here’s an important note from Sony:
As a characteristics of S-Log3, the dynamic range can be extended above 1,300%. However, Picture Profile is set to a dynamic range of 1,300% in order to maintain a balance with camera performance. Under these conditions, the maximum value of video output is 94%.
This means, anything above 94 IRE will clip, and you MUST have everything below this point. This is the key disadvantage of S-Log3 over S-Log2, there’s no highlight roll-off, it just clips. However, they both have equal dynamic range, so for the correct exposure system, they should for all purposes deliver similar results at least as far as dynamic range is concerned.
What is the difference between S-Gamut3.Cine and S-Gamut3?
There are two color spaces available for S-Log3:
- S-Gamut3.Cine
- S-Gamut3
Here’s a quick chart for reference:
Both color spaces are much bigger than Rec. 709 and even DCI-P3, however, note this important message from Sony:
-
[Cine] setting is easier to use than [S-Gamut3], because it limits the color space to a more practical range than that of [S-Gamut3]. It is recommended in cases where [S-Gamut3], a wide color space, is not required.
-
S-Gamut3 setting has a wider color space than that of [S-Gamut3.Cine]. It is suited for converting images to a format with a wide color space like BT.2020. Depending on the type of camera, the entire [S-Gamut3] color space may not be supported.
… If you would like to apply print film emulation, please increase saturation to about 1.4.
White point for both S-Gamut3.Cine and S-Gamut3 is D65.
Which is better? Sony recommends:
We recommend using S-Gamut3/S-Log3 for ACES as recording of 10bit MXF. S-Gamut3.Cine is narrower than S-Gamut3 and good for DCI-P3 grading.
Here’s my detailed comparison between S-Gamut3.Cine and S-Gamut3:
Notes:
- At one point I say 2 stops over and 3 stops under, it’s a slip-up.
- The ACES IDT for S-Gamut3/S-Log3 is available in the new version of Davinci Resolve
Takeaway:
If you’re using Resolve and want to grade in ACES, you might want to use S-Gamut3; but for the purposes of this guide I’ll be using S-Gamut3.Cine because it gets to better skin tones faster. If you’re new to this and want to start trying, I suggest you start with Gamut3.Cine and forget about S-Gamut3 until further notice.
If this situation changes in the future, I’ll update this section and let you know.
S-Log3 vs S-Log2
The following video was made for the Sony a7S, and explains some important concepts that I will assume you understand when we look at exposure for S-Log3:
- Tonality and texture
- ETTR
- Noise
- Lighting for skin tones
- The wolfcrow system for S-Log2
If you haven’t already, please watch it first:
About the relation of S-Log2 to white balance, and why it affects grading and the creation of LUTs, refer to the Technical Summary for S-Gamut3.Cine/S-Log3 and S-Gamut/S-Log3, by Sony:
It [S-Log3] is more like a pure log encoding than S-Log2 to provide better log based grading.
S-Gamut needs color temperature setting to select color conversion matrix. S-Gamut3…does not depend on color temperature any more.
White point of S-Gamut is D65. ACES is approx D60
It is not necessary to change the conversion formula for each EI setting.
S-Log3 is very similar to LogC
Data range is used from 0 to 1023 (from -7IRE to 109IRE). Legal range: Data range is scaled and limited from 64 to 940 (from 0IRE to 100IRE) in 10bit code value.
S-Gamut is the color space when shooting S-Log2. Here’s how they differ for exposure:
| IRE Values | S-Log3 | S-Log2 |
| Black (0%) | 3.5 | 3 |
| Middle grey (18%) | 41 | 32 |
| 90% | 61 | 59 |
The 90% white points are very close, and the major difference is the middle grey region. What S-Log3 basically does over S-Log2, in lay persons terms, is it raises the shadows more for a flatter look.
On the other hand, S-Log2 goes well up to 109 IRE (108 IRE in practice, according to the zebra), while S-Log3 stops at 94 IRE. But this does not mean it has lesser dynamic range. They both have the same DR, as this updated comparison graph from Sony shows:
So we need to test for three things:
- Does the raised shadow levels contribute to more noise for S-Log3?
- Is the 94% IRE cut-off a problem with highlight roll-off and practical shooting?
- Is the overall performance of S-Log3 better during grading?
In this lesson, we’ll deal with the first two issues, and learn how to correctly expose S-Log3. We’ll deal with grading in another lesson.
Understanding the Zone System and exposing for skin tones
The following video was made for the Sony a7S, though all its concepts apply to the a7S II as well. Please watch it first (at least until I’m done with the parts about skin tones and the Zone system):
Important: Disregard the numbers about the wolfcrow system, because the numbers for S-Log3 are different (see next video).
Errors and omissions for the above video:
In my article on full swing vs studio swing, I define full swing correctly, as between 0-1024; yet in the video, I use the term ‘full swing’ to mean full swing+super whites, which is incorrect. Please be aware of the difference, and it doesn’t mean anything in practical terms. In the video, when I say full swing, I’m always referring to full swing+super whites. This is the entire range from -7 to 109 IRE.
I mention in the article that 2+ stops is the least noisy, though evidently that is incorrect. It was a slip up. The least noisy is ETTR, and the wolfcrow system is the next best thing.
During the chart after the 11:00 mark, I show how a one stop overhead makes the dynamic range 12 stops. That is incorrect, and was a mistake I made while speeding up post. The 12 stops of usable dynamic range includes the overhead, all the way to 109 IRE.
References
I did make some bold statements during the video, and here are the references for the same:
I say that Kodak film has a usable dynamic range of 12 stops. It is from a Kodak whitepaper (motion.kodak.com): Exposing Film. Some gems from it:
Generally speaking, the latitude of KODAK Color Negative Film is about 10-12 stops.
To obtain the best exposure, err on the side of over-exposure to create a “bullet-proof” negative. It’s better to provide too much information on the negative than too little.
The entire analog image chain is designed to accommodate a normal exposure, normal processing, and normal printing. In fact, the system is nearly foolproof and endlessly forgiving when everything operates under normal parameters.
Cinematographers usually operate very close to that line of normalcy. Small adjustments … can produce interesting outcomes that provide precise and repeatable control over a great number of image parameters.
This is the foundation of the wolfcrow system.
Always attempt to get the best latitude, grain, color and sharpness from the stock you’re using. A properly exposed negative will optimize all these characteristics. Once you understand the film’s limits and capabilities, you can be more confident while making tough, on-the-spot shooting decisions. Occasionally, you will deviate from the normal exposure.
Consistent exposure minimizes dependence on the laboratory’s ability to compensate; as exposure correction always results in a trade-off in some area of image quality.
About S-Log2, I mentioned it was designed for DI workflows. This is from S-Log: A new LUT for digital production mastering and interchange applications, by Hugo Gaggioni, Patel Dhanendra, Jin Yamashita, N. Kawada, K. Endo and Curtis Clark:
S-Log is a gamma function applied to Sony’s electronic cinematography cameras, in a manner that digitally originated images can be post-processed with similar techniques as those employed for film originated materials.
Shooting in S-Log will enable the cinematographer to decide the exposure value by using a light meter.
CMOS imagers respond to incoming light in a far more linear fashion than film, thus there are no “toes” or “shoulders”.
When shooting in S-Log, as distinct from ITU-R BT.709 (Rec. 709) video gamma, a color grading process (‘look management’) is mandatory…
About the relation of S-Log2 to white balance, and why it affects grading and the creation of LUTs, refer to the Technical Summary for S-Gamut3.Cine/S-Log3 and S-Gamut/S-Log3, by Sony:
It [S-Log3] is more like a pure log encoding than S-Log2 to provide better log based grading.
S-Gamut needs color temperature setting to select color conversion matrix. S-Gamut3…does not depend on color temperature any more.
White point of S-Gamut is D65
How to expose S-Log3
And finally, we come to exposing S-Log3 on the a7S II:
Coming Soon: a quick and simple practical demonstration of using the wolfcrow system with lighting.
Takeaways
- The lower demarcation line for the a7S II, the point beyond which important objects, areas or details shouldn’t go below, is IRE 40. You can find this by using Zebras as explained below.
- As long as you follow the above rule strictly you are free to expose your scene the way you want it.
- Custom white balance using the Movie Mode.
- The color mode for S-Log3 is S-Gamut3.Cine. You can set the detail to -7 (the lowest, by default I believe). Nothing else needs to be changed.
- Due to the nature of light levels for video work you will most likely adopt an overexposure of between 1 to 2 stops. There are certain simple scenarios where even 1/3rd stop more will do, but generally, you’re better off between 1 to 2 stops.
- Which one do you pick? 1 or 1 or 1.5 or what? Just go back to the first point again: IRE 40. As long as you can keep important stuff above that, and you’re happy with how the highlights roll off, you’re good to go.
- The key is, for the same scene, keep this value constant.
How to use the Zebras
You have three things to worry about:
- 40 IRE noise line
- 1-2 stops over, which would fall between 45-60 IRE
- 94 IRE highlight cut-off
40 IRE noise line
Set C1 to Lower Limit and 50+ – Everything above 50 IRE will glow. Let’s say everything important glows at this point. You need to make sure it’s above 40, which it is, but you can’t tell yet. Reduce the exposure by turning either the aperture, shutter (rarely) or ISO three times (0.3EV x 3 = 1 stop) and the Zebras will vanish.
Now, everything that lit up earlier is now at 40 IRE+. I know this is a round-about way, but unfortunately the C1 Lower Limit doesn’t go below 50+.
Overexposing
This depends on how much you’re over exposing. The numbers are:
- 1/2 stop – 45 IRE approx.
- 1 stop – 50 IRE approx.
- 1.5 stops – 55 IRE approx.
- 2 stops – 60 IRE approx.
Remember, the IRE and stops are not 1:1, but I’m just rounding it out here. You can be more precise if you want to.
Set C2 to Standard Range and Standard at 50 (or 55, 60, 45, whatever your overexposure is), and the Range to ±2.
E.g., if you set it to 50 ±2, anything between 48-52 IRE will glow. You can be as precise as you want it. ±2 is a good number. I would not go below this and I wouldn’t go above ±5.
94 IRE highlight
Set the C2 Lower Limit to 94+ for precise checking. Anything above this will glow. You’ll need to enter Zebra and manually toggle between Lower Limit and Standard Range, but it’s not all that big of a deal.
Can it be any simpler? No, it cannot. Here’s a quick infographic from the video that shows all this in a nutshell:
FAQs
These are important topics raised by subscribers that shed more light on this lesson.
Q. What about Gamma Assist?
A. Screw that, it’s useless.
Q. Is it a good idea to tweak the S-Log3 profile?
A. No, as explained in the lesson on tweaking picture profiles.
Q. Can we use the “official’ Sony S-Log3 LUT or IDT in Resolve?
A. Actually you can do whatever you want, but the results will not match, unfortunately.
Q. Why is it so complicated??
A. Look on the bright side. You only have to learn this thing once.