Sony A7s - finding the IRE sweet spot for skintones, questions

N

Nicholas Natteau

Veteran
I recently read two very interesting posts regarding how to get the best exposure for skin tones when using the Sony A7s.

One of these includes a one hour video tutorial by Sareesh Sudhakaran:
http://wolfcrow.com/blog/how-to-expose-and-grade-s-log2-for-the-sony-a7s/
https://www.youtube.com/watch?v=jRI40Gl4I8g&index=3&list=PLF1tQrm_lzkAwGcB_tXEpTxz4blgBp5VM
The same video on youtube also includes chapter markers.

According to Sudhakaran, when shooting in S-Log2 at 3200 ISO, skin tones should be around 67-72% IRE, and if you don't have a waveform monitor, you should use the spot meter on the A7s and expose 2 if not 3 stops over so that the spot meter either displays "2.0" or flashes "+2.0". He describes this as the Wolfcrow method for nailing exposure and he explains in great detail why he believes it to be better than the ETTR (expose to the right) method.

Then there's a tutorial by Alister Chapman who cautions against overexposing in S-Log2 by more than 2 stops as he claims this results in a loss of detail in skin tones.
http://www.xdcam-user.com/2014/08/e...-on-the-sony-a7s-part-one-gamma-and-exposure/

I'm very interested to know what others who shoot with the A7s have discovered when exposing for skin tones.
What have you found to be the IRE sweet spot when exposing for light and dark skin tones? If caucasian skin tones show up on the waveform monitor at IRE 70-72% is this going too far?
For talking head interviews for example, are you seeing a loss of skin texture/detail when exposing skin tones at or beyond 70% IRE in S-Log2?

Thank you in advance for your feedback.
 
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I think you just expose slog2 for skin tones how you normally would and do that same when not shooting in slog2. Around 60-70% is about where you'd want them generally, right? I usually just eyeball it on the go and if it looks washed out, that's probably a sign you've gone too far. Lifted vs. clearly losing details and tonality.
 
Thank you cyork. I think that would be the rule in Picture Profile 4 (one of the baked in looks). But the Wolfcrow method appears to claim that you can expose for skin tones until the A7s is flashing 2.0+ over exposure. Though from what I can see on the monitor when I drive the exposure until it's reading 75% IRE or 2+ on the A7s spot meter, it does seem overexposed. Sudhakaran claims that S-Log is quite forgiving of overexposure in his tutorial. But i would agree with you that 60-70% IRE does seem safer for skin tones, even in S-Log2.
 
I am pretty sure that guy doesn't know what he's talking about, but I could be wrong.
 
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My method: I use my light meter and overexpose by one stop. That is, I set my light meter to ISO 1600 instead of 3200 and follow what it tells me. This means that with slog2 mid grey falls at IRE 48%.

The problem with using skin for setting your exposure is that it varies a lot between people. My skin is 1.3 stops brighter than mid grey, which means I put my skin at +2.3 stops (a7s +2 indicator stops blinking if I close iris by 0.3 stops). So, very close to that Wolfcrow method, but beware that there are much darker people than me, I'm basically bright greenish :p
(the upside is that you don't always have a grey card in the frame, but most often have skin)

And BTW, since my skin is 1.3 stops brighter than mid grey, setting it at +2.3 doesn't mean I'm overexposing by more than two stops. I'm overexposing by exactly one stop. Overexposing by 2.3 stops would mean my skin falls at +3.6 and yes that will create issues in the skin highlights.

And another BTW: a similar indirect method is to use white and zebras. Your usual "anything painted white" thing is 2.2 stops brighter than mid grey, which means that if I overexpose by one stop it has to fall at +3.2, which on slog2 means IRE 73%. So this method would be: setting zebras for 75% and making sure white things show them. But really, bringing a grey card and/or light meter is a better way to do it (the a7s meter is very well aligned with my reflective meter, so if you are not doing something really fancy you just need the grey card).
 
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This might be helpful:
http://provideocoalition.com/aadams/story/hitting-the-exposure-sweet-spot

Personally, if shooting in Rec.709 I tend to let Caucasian skin tones hover around 53IRE. When in Slog I overexpose 1 stop above Sony's recommendation using a Kodak grey card, same with S-Log 2. I haven't determined a value for S-Log 3 yet. With Canon C-Log I've had good luck following the white papers, placing middle grey around 33 IRE and white around 63 IRE.

For the a7s, I like the look of skin tone about 1/2 under using the cine profiles (setting zebras at 70 then closing the iris until zebras disappear completely).

What do the kids say, YMMV?
 
It depends in whether you're going for a final look in-camera or going to be adjusting in post.

The correct exposure for vieweing is around 70IRE for skin.

But if I am post processing the footage I expose to the maximum right without clipping and bring down the exposure to 70IRE for skin in post. This gives a richer image in colour tones and way less noise than getting it right in camera or pushin it up slightly in post.

Exposing to the right without clipping then adjusting exposure in post on a big screen has always gave me better results with every single camera I've used. It's a very solid exposure technique. Try it.
 
Traditional SLOG is 38% for middle grey.
SLOG 2 is 41%.
Skin tone for caucasions is exactly 10% points over that.
Therefore you should be at 51%. That's right 51%.
Remember, texture just before traditional white on the original SLOG was at 68%. SLOG2 is 71%
So a lot of folks here are overexposing by way too much.
Just let SLOG do it's work and don't use human skin tones as objective references.
 
Thank you very much everybody for all your feedback. I just started doing some tests in the last few days and it seems that overexposing by no more than 2 stops appears to be the sweet spot the way Alister Chapman described, but I could be very wrong. I'm afraid of over-exposing, so I will follow everyone's advice here in this thread. Again thank you all very much for your input.
 
Just one more question on this topic. What does a stop correspond to in IRE terms?

for example if middle grey is 32% what would one full stop (on the A7s) above 32% be on the IRE scale?
does a full stop equal 12%? 9%? increment on the IRE scale?

sorry for asking but I couldn't find an answer to this when researching via the forums and Google.
 
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