Setting proper exposure when shooting Slog ?

Soufian Ratib · May 4, 2015

Hello,

I shoot with the F3 using the O7Q+ recorder in Slog. How would you set your exposure when shooting Slog ? I mean, where do you set your skin tone, and highlights using the built in waveform ?

Thank you for any advices.

David Mullen ASC · May 4, 2015

Depends on if your waveform is reading a Rec.709 signal to the monitor or the log signal being recorded...

Soufian Ratib · May 4, 2015

Hello David,

My O7Q+ records the 10 bits uncompressed signal and shows the Slog output with no LUT applied. It also displays the waveform.

John E Clark · May 4, 2015

Hello David,

My O7Q+ records the 10 bits uncompressed signal and shows the Slog output with no LUT applied. It also displays the waveform.

For my Blackmagic Pocket, the manufacturer recommends 38.5% IRE for an 18% grey card, for their version of 'log' format, when displayed as 'log' data.

I have heard other numbers such as 40%, perhaps 35%, but basically its around there.

For how 'skin tones' or 'highlights' fall from there is dependent on the ISO and how the camera has been engineered. Alexa seems to put their 'native' ISO 800 such that there are an equal number of stops above and below the 18% grey card value.

I don't have the Alexa chart URL handy, but it is a popular topic.

I'm sure there's something similar for the Sonys and your capture device.

Phil Rhodes · May 4, 2015

It's almost invariably around 40%. I'm not such a pixel-peeper that I believe 2% matters here.

Robin R Probyn · May 5, 2015

Just use a REC709 LUT in camera or monitor .. and worry about all the other stuff.. like composition and content.. too many people worrying about wave form monitors and 2% or IRE here or there.. no one followed the ASA rating on film cans... of course some sort of level of knowledge is required.. but really you don't need to look at your wave form monitor all the time.. or actually ever..

David Mullen ASC · May 5, 2015

Personally I think it is a mistake to monitor in log except now & then briefly when you want to double-check your clipping, otherwise the problem is that log places middle grey and faces lower than what looks correct on a monitor in order to hold more overexposure range, so there is a tendency when viewing in log to overexpose in order to get highlights to look correct on a monitor meant to display Rec.709 gamma.

In log, often a white patch on a grey scale only hits 59-65% or 70% at most, which looks a bit dull and dim on a monitor.

If you monitor in Rec.709 and expose and light to make that look good, then you know you have a few more stops of information in the log recording to give you some flexibility in color-correction. And if you are particularly worried if something is clipping, just switch to log view and see.

Sony in particular wants you to place values quite low in S-Log (only 32% for 18% gray) which some people disagree with since it can lead to more noise. See these discussions:

http://www.dvxuser.com/V6/archive/index.php/t-317309.html

https://community.sony.com/t5/F5-F55/ViewFinder-LUT-vs-exposure-tools-zebra-waveform/td-p/260157

Mark Kenfield · May 5, 2015

SLOG on the F3 places middle grey at 38%. You can use false colour on your O7Q to check that your grey card is hitting 38%.

Hit that and you'll get perfect exposure and lovely results everytime.

The other alternative is to simply use a light meter and meter for 800 ISO.

Soufian Ratib · May 5, 2015

Thank you all for sharing your thoughts.

Many are talking about grey card. Why do I need one ? All I worry about is my skin tone level and highlights. Thank you

Phil Rhodes · May 5, 2015

Often correct exposure in log modes is evaluated (or at least, can be evaluated) using a grey card. But you don't need one. Monitor a Rec. 709 LUT, light to that, and all will be well. You can arguably get slightly more out of the system using a LUT that's been designed - very, very carefully - to give you something like your final grade. In either case the idea is that you can light it to the monitor, then recover at least some blown highlights in post. Toggling between the LUT and the log will allow you to evaluate which highlights are likely to be recoverable and which aren't.

P

Robin R Probyn · May 5, 2015

Not sure if your F3 has it.. but the "new" slog 3 cine Gamut has its primaries very much on the same axis as REC709/and the digital cinema "triangles ".. and so much easier to grade re colour shift.. Slog2 the green primary goes way off to the left.. and is way more than th eye can ever see anyway ! .. and so Sony have come up with Slog3.. and the smaller(although still way big enough) sub set Slog3 cine.. I would get a F5/55 or Fs7 too.. :).. make your life a lot easier.. shoot in Cine IE mode with a VF 709 LUT .. and your away to actually do the job of a DP,and not be an engineer.. losing sleep over lines on monitors..

John E Clark · May 5, 2015

Thank you all for sharing your thoughts.

Many are talking about grey card. Why do I need one ? All I worry about is my skin tone level and highlights. Thank you

The Grey Card is an industry standard for metering, and determining the exposure. A 'grey' card is relatively cheap... one can get into some expensive charts with DSC products, hundreds of dollars... but a grey card can serve to begin to understand the relationship between exposure and resulting values that are presented.

You ask about 'skin tone', but skin tone ranges from 'dark' to very 'light', and so it is difficult to set a standard by such a range.

The grey card is 18% (ok... some people quibble on that as well...), and light meters are calibrated to such as standard... ok, even that has some question...

But basically most people use 18% as the reflectivity of the grey card, and most people for digital film use the IRE graph for indicating proper exposure values.

With that in mind, 'caucasian' skin tone falls about 25-35% reflective, 'mediterranean' falls around 18%, and 'dark skin' tone may be 9%, or about +1 to -1 stops around 18% for most human skin tones.

Since I don't have a false color display, nor have I typically had a camera that has 'zebras', I've used my light meter and captured clips of grey cards, and 'cheap' color charts, using my meter.

Here's a Amazon reference for a grey card package, for $16 or so.

http://www.amazon.com/Kodak-1903061-Gray-Card-R-27/dp/B00009R7B0

Soufian Ratib · May 5, 2015

Hello John,

Thanks. Could you please provide an exemple on how you use a gray card on a daily basis ? I shoot the gray card while making sure my waveform displayes it at 25-35% IRE...I got that. Then what ? And what if my shot has no actors ?

Thank you

PS My O7Q+ and Cineroid retina EVF have false color. How do those features come into play ?

David Mullen ASC · May 5, 2015

Metering is only the beginning of figuring out the exposure; it's just one piece of the puzzle, one more piece of information. You still have to use your eyes and head to set the final exposure. You wouldn't expose a twilight scene the same way as a day scene.