Getting that S-Log exposure

[Douglas Villalba]

What's that saying? To each it's own.
I started shooting back in 1974. Needless to say that my foundation was shooting with negative or positive celluloid. I've never worked in the TV industry, so electronic measuring tools were not my forte.
I use zebras only when shooting run and gun and have no time to use a meter to make sure my highlights are not over 105 or maybe to make sure that my skin tones are not blown.
Most cameramen that had their beginnings working with video cameras feel most comfortable when using electronic measuring tools. Me, give me an incident light meter with a flat face and I'll give you precise exposure throughout the scene.
Since I do my own finishing I mostly shoot flat unless I am in the studio where I can control the light ratios to 709 specs.
I'm not trying to say that my way is the only way, I'm just saying that everyone has its own best way to set exposure.

[Walter Brokx]

To return to the question:

So using a light meter is the way to go for S-Log (or C-Log)?
Just like measure light for photography?

(The Logs look so weird ungraded... lol... it makes me hesitate to use S-Log/C-Log.
Btw, do you grade with the colorwheels to set black, mid and white levels, or do you use curves, because white is quite compressed?)

[Douglas Villalba]

There is not a one tools do it all. You use the tool that you have mastered in the past and adapt it to your shooting and post preferences for this camera.
Like I said, I use an incident light-meter with a flat face disk. I measure the highlight where I want details do the same with the shadow area that I want details and then get a reading of my main object and determine exposure.
That is what I know and it works for me. You have to see what works for you. A meter, zebras, or the marker in the middle of the screen.

[Chris Medico]

Originally Posted by Walter Brokx

To return to the question:

So using a light meter is the way to go for S-Log (or C-Log)?
Just like measure light for photography?

(The Logs look so weird ungraded... lol... it makes me hesitate to use S-Log/C-Log.
Btw, do you grade with the colorwheels to set black, mid and white levels, or do you use curves, because white is quite compressed?)

With my F3 in S-Log mode I am using a 18% grey card at 38 ire as registered by the spot meter in the VF of the F3. This is giving me great base results. I may stray a stop away from that setup but most of the time I shoot for that value and roll. It looks quite dark in the VF but grades out very nicely.

[Charles Papert]

Well, for those who are less experienced than the 30 yr vets chiming in on this subject, I'm sure there's a lot of head-scratching going on--quite a few divergent opinions going on in this thread. Complicating things is that we are apparently talking about multiple concepts: how to best expose faces as well as best overall exposure (two different things, because "exposing" a face may be a function of how one lights it, far less passive than simply setting an exposure). Also, there is run and gun shooting, there is shooting for a broadcast look, there is shooting for a dramatic look. All have very different approaches to lighting and what is considered "proper" exposure for skin tone.

I myself use a combination of waveform, false color and calibrated monitor to match between cameras and scenes, but I'm also working from a DIT station which has all of this in simultaneous display. Mostly I'm shooting in the narrative world which has a larger range of skintone exposure than broadcast, but having recently had the experience of shooting a parody of a reality show with a large cast, I had to wrap my head around high-key lighting to duplicate the look.

Even within that world, I was constantly compensating for varying skin tones amongst the cast. My intention was not to place them all at exactly the same value, but to keep them within a given range. On this Doug and I disagree. I would NOT place a very dark-skinned person under the same lighting as a very light skinned person; as that represents a possible variation of up to four stops of reflective reading, I may reduce that range to perhaps two stops (as well as potentially lighting them with different techniques). In other words, I will light the dark-skinned person hotter than a mid-range caucasian, not so much that their skin tone would end up the same tone, but so that the first individual would show detail in their face that might otherwise be lost. Likewise. I will notch it down on a particularly fair individual for the same reason. They will still read as fair, just not luminescent! If they are both in the same shot, I would endeavor to slow down the fair-skinned person via nets or good planning (such as having them positioned on the far side of the key so they receive less light).

As far as light meter goes: mine only comes out these days when I need to recreate the intensity of a given instrument (in the case of a relight between wide shot and close-up, for instance). Contrary to Douglas, I prefer the ball over the flat disc for reading faces, but as always, to each his own.

[Dennis Hingsberg]

Originally Posted by Walter Brokx

To return to the question:

So using a light meter is the way to go for S-Log (or C-Log)?
Just like measure light for photography?

(The Logs look so weird ungraded... lol... it makes me hesitate to use S-Log/C-Log.
Btw, do you grade with the colorwheels to set black, mid and white levels, or do you use curves, because white is quite compressed?)

You don't need a lightmeter Walter, but if you want to read about how I am using one with the F3 to expose my images I have posted it in my blog here with samples, and some further details about my process getting exposure here. You can also head over to Abelcine's website and watch Andy's video where he rates the ISO of the F3 and see first hand how to use a grey card and a light meter with your F3 to determine your working exposure. So for example I already know that I need 42 foot candles or F4, to expose my grey card at 50% when my camera is set to 0db, 24fps, 180 degree shutter mode (or 1/48th). I can light my scene before anyone holds a grey card or any talent sits down. I can walk through an alleyway in the afternoon and know how much light is there to get me my grey. Again, grey is just a baseline. Shoot a dark fella then open up a bit. Shooting casper the ghost? Then close down some. Whatever you think looks good in the end.

But forget light meters all together because that will spark a whole other debate about incident vs. reflective metering..., the method Chris Medeco suggested (exposing your grey card at 38%) is also the same as what this guy did on his F3/SLOG production: http://www.dvinfo.net/forum/sony-xdc...-shoot-f3.html which you can do using a waveform monitor or the brightness display (marker function) built right into the F3. The main point I've been trying to stress here is to shoot for consistency so the quality shows in your work.

38% is not a magic number, you can set your middle grey to 30,35,40,45, 60 even.... but where you decide to put your "middle grey" will depend on a few things: 1.) What else is going on in the scene light or contrast-wise that you want to protect? ie. With 13.5 stops of dynamic range you have the choice of shooting 6 stops bellow middle grey and 6.5 above (maybe to get more range in your highs) or 8 stops below middle grey and 4 stops about middle grey - perhaps you are shooting a lower lit scene where the contrast ratio is low to begin with. 2.) The level of your grey will shift based on what you are shooting, whether it be a boat, a person, a room, or just the mood or look you are trying to acheive.

Charles really hit the nail on the head about something and I wish it came up sooner. There is definitely a difference between establishing a "broadcast" look and a cinema look in terms of exposure - perhaps that's where some differences are surfacing here. I worked in TV broadcast in both the studio and ENG as cameraman and it was never really about what IRE the skin was, we exposed for the highlights at 100 and just shot. This resulted in far brighter images (like you see on 6 o'clock news) then the types of images you might see in dramatic type of film work.

[Alister Chapman]

The big issue most people have when working with log and exposing mid grey at 38 is that when you look at it on a standard monitor without any lookup tables it looks underexposed. The assumption therefore is that it is underexposed or in some way too dark to ever look right, because that's what people used to working with conventional gammas have become programmed to believe over many years from their experience with conventional gammas. So, for confidence you add a lookup table which converts the log to a Rec-709 type gamma and now the image looks brighter, but as it now has to fit within Rec-709 space we have lost either some of our high end or low end so we are no longer seeing the full range of the captured image so highlights may be blown out or blacks may be crushed.
It's important for people to understand the concept of gamma and colour space and how the only way to truly see what a camera (any camera) is capturing is to use a monitor that has the same gamma and colour space. Generally speaking lookup tables don't help as they will be taking a signal with a large range and manipulating it to fit in a small range and when you do that, something has to be discarded. If you were to take an F3 set to S-log and expose mid grey at 38 and show that on one of the nice new Sony E170 series monitors that have S-log gamma and place that next to another F3 with Rec-709 shooting mig grey at 50% and a similar but conventional 709 monitor the lower and mid range exposures would be near identical and the S-log images would not look under exposed or flat. The S-log images however would show an extra 2 stops of dynamic range.

Furthermore it has to be remembered that log is log, it is not linear. Because of its non linear nature less and less brightness information is getting recorded as you go up the brightness range. As our own visual system is tuned to be most accute in the mid ranges this is normally fine provide you expose correctly putting mid tones in the more linear parts of the S-log curve. Start putting faces to high up the S-log curve and it gets progressively harder to get a natural look after grading. This is where I think a lot of people new to log stumble. They don't have the confidence to expose faces at what looks like a couple of stops under where they would with a standard gamma, so they start bringing up the exposure closer to where they would with standard gamma and then have a really hard time getting faces to look natural in the grade. Remember that the nominal S-Log value for white is 68 IRE. Part of the reason for this is that above about 70 IRE the amount of compression being applied by log is getting pretty extreme. While there is some wriggle room to push your exposure above or below the nominal mid grey at 38 it's not as big as you might expect, especially dealing with natural tones and overexposure.

If you do want to shift your middle grey point this is where the EI S-log function and a light meter comes into it's own, it's what it's designed for.

First something to understand about conventional camera gain, dynamic range and latitude. The latitude and sensitivity of the F3 is governed by the latitude and sensitivity of the sensor, which is about 13 stops. Different amounts of gain or different ISO's don't alter the cameras latitude, nor do they alter the actual sensitivity, only the amount of signal amplification. Changing the actual gain or ISO will change the dynamic range. Increasing the camera gain will reduce the dynamic range as something that is 100 IRE at 800 ISO would go into clipping if the actual camera gain was increased by 6db (taking the ISO to 1600) but the darkest object the camera can actually detect remains the same. Dark objects may appear brighter, but there is still a finite limit to how dark an object the camera can actually see.

EI S-log is different (and EI modes on other cameras). Let's consider how it works. In EI S-Log mode the camera always actually outputs at 800 ISO from the A/B outputs. It is assumed that if your working with S-Log you will be recording using an external 10 bit recorder connected to the A/B outputs. 422 is OK, but you really, really need 10 bit for EI S-Log. At 800 ISO you have 6.5 stops of over exposure and 6.5 under when you shoot mid grey at 38 or expose conventionally with a light meter.
Now what happens when you set the camera to EI 1600? Realise that the camera will still output at 800 ISO over the A/B outputs to your external recorder, but also note that 6db gain (1 stop) is added to the monitor output and what you see on the LCD screen, so the monitor out and LCD image get brighter. As the cameras metering systems (zebras, spot meter, histogram) measure the signal on the monitor side these are also now offset by +6db or + 1 stop.
As the camera is set to EI 1600 we set our light meter to 1600 ISO. If we make no change to our lighting the light meter would tell us to stop down by one stop, compared to our original 800 ISO exposure.
Alternately, looking at the camera, when you switch on EI 1600 the picture gets brighter, your mid grey card would also become brighter by one stop, so If we use the cameras spot meter to expose our grey card at 38 again we would need to stop down the iris by one stop to return the grey card to 38 IRE(for the same light levels as we used for 800). So either way, whether exposing with a light meter or exposing using the cameras built in metering, when you go from EI 800 to EI 1600 for the correct exposure (under the same lighting) you would stop down the iris by one stop.
Hope those new to this are still with me at this point!
Because the cameras A/B output is still operating at 800 ISO and you have stopped down by one stop as that what the light meter or camera metering told you to do because they are operating at EI 1600, the A/B output gets darker by one stop. Because you have shifted the actual recorded output down by one stop you have altered you exposure range from the original +/- 6.5 stops to + 7.5 stops, -5.5 stops. So you can see that when working at EI 1600 the dynamic range now becomes + 7.5 stops and -5.5 stops. Go to EI 3200 and the dynamic range becomes +8.5 stops and -4.5 stops.
So EI S-log gives you a great way of shifting your dynamic range while giving you consistent looking exposure and a reasonable approximation of how your noise levels are changing as you shift up and down the dynamic range.
EI S-Log doesn't go below 800 because shifting the dynamic range up the exposure range is less beneficial. Lets pretend you have an EI 400 setting. If you did use it, you would be opening up the iris by one stop, so your range becomes +5.5 and -7.5 stops compared to your mid grey or light metered exposure. So you are working with reduced headroom and you are pushing your mid range up into the more highly compressed part of the curve which is less desirable. I believe this is why the option is not given on the F3.

[Dennis Hingsberg]

Originally Posted by Dennis Hingsberg

38% is not a magic number, you can set your middle grey to 30,35,40,45, 60 even.... but where you decide to put your "middle grey" will depend on a few things: 1.) What else is going on in the scene light or contrast-wise that you want to protect? ie. With 13.5 stops of dynamic range you have the choice of shooting 6 stops bellow middle grey and 6.5 above (maybe to get more range in your highs) or 8 stops below middle grey and 4 stops about middle grey - perhaps you are shooting a lower lit scene where the contrast ratio is low to begin with. 2.) The level of your grey will shift based on what you are shooting, whether it be a boat, a person, a room, or just the mood or look you are trying to acheive.

Actually I should have mentioned that 38% is where SONY rates middle grey when in SLOG mode according to their SLOG white paper. So if nothing else, you just want decent and consistent exposure without getting all scientific, and perhaps you can't monitor LUT'd outs and are forced to look at ugly SLOG on a standard monitor - then use your grey card, set your cam of for 38% and be on your way. Here's a SLOG curve taken from Abelcine's video showing where middle grey would sit on a scope:

[Mark McCarthy]

Since watching Alister's excellent presentation at NAB (watched online) - I have been using my grey card on at all times when out and about (it's tucked into my back of my trousers!) - and my footage has been looking, in my opinion at least, lovely. I find it much easier to shoot with S-LOG when indoors but I guess this will always be the case. Have a look at this clip, shot using S-LOG.

'Let your light Shine' short demo version. on Vimeo

I think aside from the dynamic range that is gained, the biggest asset of it is how the camera handles and represents skin tones, I think they look fantastic. Editing now is quicker for me as well (using Sony Vegas), as I have about 10 color curves I've put together and I simply choose the curve that looks closest to the 'correct' one, then I just make small adjustments to that.

Thanks for the time you put into the forum Alister.

Sparky

[Douglas Villalba]

How has Slog help on this video?
What was the range from highlights to shadows?
I can see highlights blown and shadows without details.
Is it Vimeo or does it have to treated in a more powerful program like Resolve or Color?

[Alister Chapman]

One of the things I find with S-Log is that you get very pleasing highlights on faces as opposed to the sometimes glaring highlights that the abrupt knee with standard gamma or rapid compression with cinegamma.

[Bruce Schultz]

Very interesting and informative thread going here.

If everyone reading this thread thinks that it's nervous time exposing the crossover point 18% grey at 38 because the images look underexposed, then just wait until you get a chance to use a 4K Sony F65 camera which recommends setting it at 32 for S-Log 2. Yes, there is an S-Log 2 designed specifically for the F65. It differs quite a bit from the F3 and F35 S-Log 1 because the huge 8K CMOS chip in the F65 can stretch out that exposure so much more.

I for one have just about had it with producers, directors and craft service people who see my S-Log Only monitor and tell me that I'm underexposed on those faces. You should see what S-Log 2 at 32 looks like. I'm planning on banishing LUT's from my sets and insist that the pertinent people LEARN what S-Log is, what it looks like, what it does, and why they should just get over having a picture perfect image on their video village monitors because somehow a gallon of image has just been crammed into a pint container for them. If you know what you are seeing when you are looking at an uncorrected S-Log 1 or 2 image and it is apparent that all of the detail is there, nothing that counts is overexposed or actually underexposed , then why bother trying to look at it any other way? You know it's going to grade out perfectly. The exception would of course be for any specialized look like a bleach bypass, blue moonlight or other looks you are going to use for that scene later can be replicated in a LUT on set, and that's a good use of them. For straight REC709 monitoring, it's a complete waste of time IMHO.

Sorry for the rant, but I've watched so much time, energy and money wasted on tweaking various LUT's on set - time that could have been better spent on rehearsing or lighting or finishing earlier.

[Alister Chapman]

On the F65 S-log 2 is a LUT! If your shooting 4K the camera records linear raw, there is no gamma. S-log 2 is provided as a LUT on the HDSDI out and viewfinder because without a LUT the image would be mostly black. Even using S-Lg 2 you still need to use the over/under button to see the high and low end of the exposure range.

[Bruce Schultz]

Alister, you are correct that S-Log 2 is a LUT when the camera is recording RAW or RAW LITE, it is in effect though when you are using the F900 or REC709 gamuts to record.

[Charles Papert]

Bruce, trying to understand your rant. Are you saying that producers and directors are getting deeply involved/micromanaging your LUT creation? Why are they even seeing the log images to begin with if you are making LUTS on set? And are you suggesting that by "banishing LUTS" you would make everyone view log images, or just straight REC709 all the time?

I have just had very different experiences so I'm trying to wrap my head around what you are describing.