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general questions on the zebra feature on cameras

exposure zebra menu

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#1 davide sorasio

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Posted 30 October 2015 - 11:17 AM

Hi everybody. I have a couple questions on the zebra features of digital cameras. I know it's a feature that helps you seeing which part of the frame correspond to a certain IRE level. What I'd like to know is which level of IRE should the zebra set to. I know it is a customizable feature but I'd like to know generally what should the zebra level set to. Which IRE value corrspond to over exposed to a point of loosing info? And why is there an option to set 2 zebras at the same time?Is it because it's common to set it for a high value of IRE and a low value at the same time in order to check over and under exposure at the same time?

Thanks so much in advance for the help!


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#2 David Mullen ASC

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Posted 30 October 2015 - 12:07 PM

Generally I've found that 70 IRE is the lowest level I could set a zebra, at least it was 10 years ago when I last used a broadcast video camera. 70 IRE in Rec.709 is a light grey similar to a pale Caucasian face in full exposure lighting like in a newsroom, in an interview. It's also about what a cement sidewalk reads when exposed normally. So I found it useful when setting exposures on the run, I'd stop down just so the 70 IRE zebras disappeared on a face or only appeared on the hotter spots of the face, or I'd use a sidewalk as a starting point in setting exposure. However many operators can't stand 70 IRE zebras since they appear over many highlights in the shot. As a DP/operator, I was happy for the exposure information.

If you set two zebras, one at 70 and the other at 100 IRE, then you'd find that when in Rec.709 and pointing the camera at an 11-step grey scale, you'd get zebras in the grey patch one-stop over 18% grey and another over the white patch, which can be useful info though I find two zebras too confusing to look at.

Trouble today is that if the camera is recording log where white itself is at 70 IRE or even 65 IRE, you can't set a zebra to appear low enough for skin tone exposure so it would only be useful for setting normal whites (5-stops over 18% grey), not super-whites. So I think zebras only work for run-and-gun exposure setting when viewing Rec.709.
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#3 Brian Drysdale

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Posted 30 October 2015 - 12:17 PM

It's not unusual to set zebras at 100% or 95% (according to preference ) for the peak white and 70% for Caucasian skin, although the latter is a bit varable depending on the subject's tan.Howeve, that only applies for rec709, when shooting log different levels apply.

 

A scene mat not have a peak white, however, skin is pretty common, so can be used as a reference.

 

Having a correctly set up monitor assists in the correct exposure, as does a wave form monitor.


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#4 davide sorasio

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Posted 30 October 2015 - 12:47 PM

Thanks guys! I was just reading somewhere on the internet that 15 IRE equals to a stop? is that true?


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