S-Cinetone is a rather clever gamma curve and the way you expose it alters the way your final images look. Exposing brighter doesn't just make the picture brighter, it also reduces the contrast, making the image look flatter. Exposing a little darker has the opposite effect increasing contrast.
This happens because the S-cinetone curve has a very gentle highlight roll off that starts a bit lower than most other gamma curves and a toe at the lower end that increases contrast as you go down into the shadows. It is also worth considering that S-Cinetone was designed to produce a more film like look than normal Rec-709. If you look at most movies you will find that faces and skin tones are typically much darker than is normal for daytime TV. Where a face my be exposed around 70% for TV, in movies it is not at all uncommon for faces to be closer to 50%. In my opinion S-Cinetone tends to work best when faces are exposed around 60%.
If you expose faces at 70% with S-Cinetone they will be in the highlight roll off area. This causes the skin tones to flatten, have reduced contrast and generally look less natural. Bring faces and skin tones down to 60% and the contrast will increase and the face will look much better. This lower brightness isn't under underexposure, S-Cinetones mid range is supposed to be a bit darker. So, it won't be noisy and you'll get the added benefit of a larger highlight range.
When using zebras with S-Cinetone I set mine to 60% as this gives me a look that I like. I would never go as high as 70%, 65% would be my upper zebra limit. At the lower end I may consider going down as far as 57% for a drama or narrative piece.
There is no "one-fits-all" exposure for S-Cinetone so you might need to experiment a little to see what works for you. Perhaps for TV news you might go for 65% as this won't look dark against regular 709 cameras shooting at 70%. If you are shooting a drama using S-Cinetone and feeling brave you could go as low as perhaps 55-57%.
Over exposing is rarely a good thing with something where grading or colour management isn't an integral part of the delivery process. S-Cinetone is designed to look great directly out of the camera, but it is not vanilla Rec-709, so it works best with slightly different (lower) brightness levels to 709. The FX3/FX6/FX9 etc with S-Cinetone all behave exactly the same.
Well, in my opinion, the discredited old-fashioned practice of exposing for faces has no place in today’s production environment where actors, models, and other talent come from many different races with a wide range of skin tones. Not only is it a demonstrably inaccurate way of judging exposure, there’s also something a little offensive about assuming everyone in the world has the same skin tone, or worse, that one shade of skin is more important than others.
When I read statements like “S-Cinetone tends to work best when faces are exposed around 60%.”, it makes me wonder WHO’s face are they talking about? If 60% works for ALL faces, I’d love to hear an explanation of how that could be true. For example, let’s say I was hired to shoot interviews with a couple of today’s most popular comedians: Jim Gaffigan and Kevin Hart. Will 60% work for both faces, or just one? If just one, which one? And what are you going to do about exposing correctly for the other face?
And what if you’re shooting b-roll, a product shot, or something else that has no human faces? How are you going to judge exposure and keep that exposure target consistent from shot to shot?
Personally, I always set my exposure based on bright reflected whites (often called 90% white). In an interview situation, after all the lighting is set, I will always have the talent hold a white card in front of their face for a couple seconds, set the exposure based on zebras in my viewfinder, drop the card, and then I’m ready to roll with a perfectly accurate exposure – regardless of the shade of the person’s face. It is a fast, very accurate, non-offensive way of shooting that virtually eliminates guessing or making judgement calls.
Zebra + White Card is just as accurate as a traditional incident Light Meter, which has been the preferred method of judging exposure in cinematography and photography for more than a century. In other words, the camera's exposure is based on how much light is falling onto the scene rather than how much light is being reflected off of an object (face) that unknown brightness. The advantage today with electronic cameras, is that we don't have to carry around a light meter or a waveform monitor or a broadcast-quality grading monitor to set exposure. We just need zebras and something white in the scene.
To expose for S-Cinetone, I recommend setting Zebra2 at 85% and allowing just a touch of zebra to show on bright reflected whites.
A white card will always be more "accurate" than skin tones if you always want to hit a very specific brightness for white. But when we look at an image we don't tend to be looking to check whether a white card has been exposed at exactly the right level but rather whether the image looks balanced. This is why incident light meters have always used the average illumination for a scene as the reference, not just white or black, but more importantly the average of everything in between.
For me what is more important with a "what you see is what you get" gamma like S-Cinetone is whether faces look bright enough to be seen well, but not so bright that they look over exposed and equally not so dark as to look dim/underexposed. If I'm shooting a darker face then I might expose a touch brighter, when shooting a very bright, pale face it may be better to expose a touch darker. A white card will get me in the ball park for the scene, but what really matters is the subject and I will ignore my white value if my talents faces look better exposed brighter or darker. If I have scene with multiple faces then I will likely take the best compromise that makes all the faces look as good as possible and generally if that is a mix of bright pale to dark browns there will be an average value.
60% zebras for faces is a guide and most people are well aware that even across one individuals face there will be a wide variation in tone. Generally there isn't as much brightness variation between different skin tones as one might expect, the biggest difference tends to be saturation. But using zebras at a certain level for "average" skin tones is widely adopted because faces are often the most important part of a shot and if those faces are too bright or too dark they become unpleasant to view, regardless or skin colour. Even in countries where darker skin tones make up the majority of the populace the same zebra values are used as in northern countries where pale skin is predominant as on a very limited range Rec-709 display these values represent a sensible brightness for a face, generally 1/2 to 2/3rds of the way up the brightness range, not too dark, not too bright. And don't forget that the usual 10% zebra window will mean that in reality Zebras at 60 will encompass 55-65% which is a pretty big range that's going to mean that if you have a light skinned and dark skinned person side by side, in the majority of cases zebras will appear on both. But I would hope that most people appreciate that faces come in many shades and have sufficient sense to adjust how they expose faces to both the face and the environment it is in.
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