What do the FX3 and FX30 zebras measure when using the Cine EI modes?

This is a question that keeps popping up:

What do the zebras measure when shooting S-Log3 using the CineEI modes in the FX3 and FX30?

The convention for zebras with the majority of cameras is that zebras are a viewfinder applied measurement. As such they almost always measure the “viewfinder” image. As the LCD on the FX series cameras is in effect the viewfinder, the zebras measure what you see on that screen. So, when you have a LUT on, the zebras measure the LUT, not the S-Log3.

Common ways to use the zebras include measuring skin tones, which for the default s709 LUT will be somewhere in the region of 60% depending on the face brightness. You could also use the LUT’s to measure the brightness of a white card or white piece of paper which should be around around 81% for a proper white card or 83% for white paper.  

You could also use Zebras to indicate when you are close to clipping Depending on the LUT that you are using the peak LUT output will typically be at 100%, so a common usage would be to have Zebra 2 (which measures from the zebra point and everything above) set to a touch below 100 to act as a clipping indicator. BUT it must also be remembered that depending on the Exposure Index in most cases the LUT will have a lower highlight range than the S-Log3 recordings. So, when your highlights hit 100% on the LUT there may still be available headroom in the S-Log3 recordings. If you end up backing off your exposure every time the LUT clips you may be missing out on the full recording range and un-necessarily bringing the mids and shadows down. So, my preference is to measure the exposure of a white card or skin tones and to get the mid range and shadows right, rather than obsessing over small amounts clipping.

The s709 LUT does fit the full highlight range of the S-Log3 into it’s output. But as there is only a tiny difference between +5 and +6 stops (approx 1.5%) it is very difficult to determine what is clipped and what is 1 stop below clipping. +4 stops above middle grey is output at 93% and +6 above middle grey is at 98% so it becomes very difficult to see what is really going on in the highlights via the LUT when the top 2 stops are crammed into just 5% of the recording range. Zebra 2 set to 95% (for example) would appear over 1.5 stops below clipping, even if set to 97% zebras will show almost a full stop below clip.

It is one of the frustrations of the FX3/FX30 that there is no way to monitor via the LUT and measure the S-Log3 at the same time.

5 thoughts on “What do the FX3 and FX30 zebras measure when using the Cine EI modes?”

  1. If I turn off the viewfinder LUT, will my zebra and histogram be accurate?
    As an example – zebra set to 95% – frame a landscape, expose for the tops of the sunlit clouds at 95% – make sense?

    1. The zebras and histogram are always accurate, whether measuring the LUT or the Log. But if you are measuring the S-Log3 with zebras (viewfinder LUT off) then clipping is at 94%, so you’ll want your zebras below 94%. But generally I wouldn’t expose for the highlights as it’s the mid range that’s important and underexposed mids and shadows will be noisy and grainy which will be far more objectionable than a few clipped clouds.

  2. Hey Alister,

    do you have an exposure guide for your own slog3 venice LUTs?
    I played with them as MLUTs on my FX30 and discovered that the -1.5p Version gets closer to the true Clipping point of the S-Log3 than the default s709 LUT. On the other hand skintones seem to be right at a much lower value (around 40 ire).
    Could you further elaborate on this? This would help me out a lot since I like your -G1 Look more than the default s709 and would love to use it for monitoring.

    1. LUT’s with more contrast than the S-Log will always have a highlight roll off so they won’t always show the full dynamic range of what is being captured, so it is quite normal to find that it isn’t until you expose brighter via a lower exposure index or an offset LUT that the LUT will clip at the same time as the Log.

  3. Hello Alister, 2 questions.

    Is there any disdavtages shooting SLOG 3 in a custom profile on the fx3 (with the correct settings like the pp mode it was before) instead of using the log mode that came out in the recent updates? I don’t care for EI since I am shooting solo.

    If I have LUT off and gamma display assist on, the zebras are measuring the log and not the s709, correct?
    Thank you!

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