How to expose correctly using the Atomos Shogun – S-Log2

In this lesson we’ll learn how to expose S-Log2 using the Atomos Shogun.

The test is similar to what I used to explain the Picture profile modes, and I’ll be using a DSC Labs OneShot as reference. The lighting is pure halogen, custom white balanced at 2900K. The light is from the left that is why there is a small but negligible fall-off (the real world barely has zero fall-off).

The spot meter in the camera was measured within the large grey patch for exposure. Exposure settings are available in the first image.

Middle Exposure Test

First, we’ll expose S-Log2 for 0.0, or ‘middle-exposure’. Here are the results (click to enlarge):

Slog0

Notes:

  • Middle grey falls at about 35 IRE, which is fine. The theoretical middle grey is 32 IRE for S-Log2.
  • Color information is compressed so you can hardly see it on the Vectorscope! But the RGB parade tells us the information is there.
  • The zebras are useless, because they don’t go below 50 IRE.
  • The false color tools tells us middle grey is at ‘dark grey’ (24-43 IRE) and white is at ‘light grey’ to pink (54-60-ish IRE). There’s lots more room at the top!

Wolfcrow System Tests

Now we overexpose middle grey by three stops (+3), and these are the results of the wolfcrow system:

SlogWC

The same thing but the chart is not turned for the color patches (exposure is same, nothing has changed):SlogWCColorChart

Notes:

  • The spot meter is actually blinking at +2 and is three stops over.
  • The waveform tells us middle grey falls on 70 IRE, which is where it should be for the wolfcrow system. You can see that highlights have been clipped at 105 IRE. What is instructive is that the white patch is only showing about 95 IRE.
  • Under the color chart, the black is almost touching 20 IRE, which is where it should be.
  • The darkest skin patch lights up at Zebra 50 IRE, and the darkest skin will fall at above 40 IRE, as per the wolfcrow system. This actually will help with dark skin, which was impossible to pull of with the zebra on the A7s.
  • The Zebra at 70 shows up on the grey patch.
  • The false color tool shows the lightest grey on the grey patch (58-77 IRE). However, the blacks show up as black, instead of deep blue or purple. This must be a quirk!
  • Caucasian skin can creep into the yellow zone, though I would only advise this if the highlights are not blown out.

The false color tool is not always a precise tool for exposure, as we have seen earlier. It has its uses, but is more confusing than necessary.

The biggest problem is the fact that you can’t configure the false colors in the way you want, so it becomes very restrictive. Secondly, you can’t judge blown highlights (everything’s red!) and crushed blacks (why is it showing up as black?) very accurately as well.

Underexposing and blacks

Here’s how a scene would look like underexposed:UnderExposedRealworld

And here’s a scene totally underexposed:UnderExposed

You can see that the blacks are never truly black in S-Log2, and this was explained in the guide to exposing S-Log2.

What is strange is that the false color shows up as dark blue (2-8 IRE) here, but was showing up as black in the earlier tests. It never goes purple in S-Log2, and you never have to fear crushing the blacks.

Overexposing

When you overexpose, this is what the false color tool looks like:

OverExposedAs you can see, anything above 100 IRE is red, even though the A7s can go up to 105 IRE. You can’t judge blown highlights using this tool.

However, that doesn’t mean things are bad. Here’s the actual image (full UHD 1.5 MB) of the earlier test (click to enlarge):

ShogunActualUHDImage

 

Note, some level of color compression occurs because I had to compress to JPEG to reduce space. The actual image is way ‘smoother’ and totally filmic in its transitions.

You can actually allow this camera to blow out, and it handles it exceptionally well. Compare it to the sea of red in the earlier false color tool. Totally misleading.

Are there any image quality differences between the HDMI feed and the internal XAVC S?

No.

Some users and reviewers have stated that the Prores version is more contrasty. The A7s outputs a similar signal for both, and the Atomos Shogun even displays a matching waveform.

To know the details please refer to the Atomos Shogun review.

How to expose for S-Log2 using the Atomos Shogun

Here’s the easy way:

  1. Use the wolfcrow system.
  2. Keep middle-grey at about 70 IRE and use 105 IRE to check for blown highlights. Use the waveform and/or zebra for this.
  3. Make sure the RGB parade lines up – this is a quick indicator of white balance issues. Forget the vectorscope.
  4. If using the false color, middle grey should be at ‘lightest grey’, and really dark skin should not fall below green. Avoid using the false color tool as a reference.

Click on the link below to the next lesson or head over to the main menu (above). If you need help with something, feel free to send me an email. I’ll try to get back to you as soon as possible.