Zebra range and exposure question

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Felix Steinhardt

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Zebra range and exposure question

PostSat Aug 25, 2012 9:52 pm

Hi,

I wonder which zebra levels can be set in the camera. On the video cameras I usually use zebra goes only down to 70 which is pointless when I want to expose for a greycard.

Can I set zebra levels to 50 or 45? On Sony cameras I´m used to expose greycards to 45 IRE when using cinegamma. I know it´s different with other gammas, cameras, for example Slog should be exposed to 35 IRE. What´s the correct exposure level for a greycard on the BMCC when shooting RAW?
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John Brawley

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Re: Zebra range and exposure question

PostSat Aug 25, 2012 10:37 pm

Felix wrote:Hi,

I wonder which zebra levels can be set in the camera. On the video cameras I usually use zebra goes only down to 70 which is pointless when I want to expose for a greycard.

Can I set zebra levels to 50 or 45? On Sony cameras I´m used to expose greycards to 45 IRE when using cinegamma. I know it´s different with other gammas, cameras, for example Slog should be exposed to 35 IRE. What´s the correct exposure level for a greycard on the BMCC when shooting RAW?


At the moment the zebra only goes down to 75%. The other thing to note is that it works of the sensor's LINEAR data. No gamma is applied to the zebra setting. That means when you set it to clipping, at 100%, it's basically showing you sensor clip IRRESPECTIVE of the ISO you might have set. This has more ramifications when shooting ProRes and DNx.

I know there are other exposure tools being looked at for down the road. For the moment Zebra works very well for me. There's so much DR that as long as I know what's clipping or near clipping, I know everything else is being captured.

jb
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Felix Steinhardt

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Re: Zebra range and exposure question

PostSat Aug 25, 2012 10:53 pm

The problem for me is consistency. Getting the same exposure of a face while shooting different angles or FOV when lighting must be changed.

Spotmeter, Zebras (not just for showing clipping), false colour...anything would help.
Making zebras available from let´s say 30-100 IRE can´t be too difficult... ;)
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Kristian Lam

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Re: Zebra range and exposure question

PostSun Aug 26, 2012 6:43 am

Felix wrote:The problem for me is consistency. Getting the same exposure of a face while shooting different angles or FOV when lighting must be changed.

Spotmeter, Zebras (not just for showing clipping), false colour...anything would help.
Making zebras available from let´s say 30-100 IRE can´t be too difficult... ;)


Yes, you're right. It's not difficult and we'll look into it. The problem here is to find the right balance. There will be a million and one things we can do that is not difficult but it does add up. The good thing is the nifty little USB port next to the SSD slot. It allows up to upgrade the camera with new features.
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Andreas Kaufmann

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Re: Zebra range and exposure question

PostSun Aug 26, 2012 5:47 pm

Kristian Lam wrote:
Felix wrote:The problem for me is consistency. Getting the same exposure of a face while shooting different angles or FOV when lighting must be changed.

Spotmeter, Zebras (not just for showing clipping), false colour...anything would help.
Making zebras available from let´s say 30-100 IRE can´t be too difficult... ;)


Yes, you're right. It's not difficult and we'll look into it. The problem here is to find the right balance. There will be a million and one things we can do that is not difficult but it does add up. The good thing is the nifty little USB port next to the SSD slot. It allows up to upgrade the camera with new features.



Sounds very promising, Kristian. Glad of your forum presence here!
Keep up the good work! Cinema revolution is nearing ..
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Noel Sterrett

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Re: Zebra range and exposure question

PostSun Aug 26, 2012 6:58 pm

John Brawley wrote:
That means when you set it to clipping, at 100%, it's basically showing you sensor clip IRRESPECTIVE of the ISO you might have set.

jb


I'd be delighted if it's really a RAW sensor Zebra. Is that what you are saying?

Cheers.
Noel Sterrett
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John Brawley

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Re: Zebra range and exposure question

PostSun Aug 26, 2012 9:17 pm

Noel Sterrett wrote:
John Brawley wrote:
That means when you set it to clipping, at 100%, it's basically showing you sensor clip IRRESPECTIVE of the ISO you might have set.

jb


I'd be delighted if it's really a RAW sensor Zebra. Is that what you are saying?

Cheers.


It is.

JB.
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Felix Steinhardt

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Re: Zebra range and exposure question

PostSun Aug 26, 2012 9:56 pm

And by RAW you mean ISO 800, right?

That leads me to another question. Does the BMCC always record in ISO 800 no matter what you set the ISO while recording (like a RED camera?)

Or is the signal amplified and then recorded?

That makes a big difference
If ISO is just metadata, I could record in ISO 1600 and later decide to go back to 800.
And it would mean that ISO 400 and 200 are only kind of "emergency ISOs" if you forget bringing NDs because if the camera always records 800 you wouldn´t gain any highlight detail when going down to 200.
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Noel Sterrett

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Re: Zebra range and exposure question

PostSun Aug 26, 2012 10:41 pm

Felix Steinhardt wrote:And by RAW you mean ISO 800, right?


I don't believe that is what he is saying. The ISO setting does not change the characteristics of the sensor. The sensor clips at the same point ( combination of f-stop, shutter speed, illumination) regardless of the ISO setting.

However, the ISO setting does effect the SDI output. So a waveform monitor connected to the SDI output would vary with ISO, while the RAW DNG's would not.

If you are recording ProRes files, an SDI monitor with a built-in waveform display, such as the new Marshall 5.6MD, would be very useful to correctly set the ISO. But if you are recording RAW DNG, the camera Zebra will correctly indicate the point of clipping of the sensor (and the SDI output will not).

What I am not yet clear on, is which (RAW sensor or SDI) is displayed with the Ultrascope.

Cheers.
Noel Sterrett
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John Brawley

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Re: Zebra range and exposure question

PostMon Aug 27, 2012 1:35 am

Noel Sterrett wrote:
Felix Steinhardt wrote:And by RAW you mean ISO 800, right?


I don't believe that is what he is saying. The ISO setting does not change the characteristics of the sensor. The sensor clips at the same point ( combination of f-stop, shutter speed, illumination) regardless of the ISO setting.

However, the ISO setting does effect the SDI output. So a waveform monitor connected to the SDI output would vary with ISO, while the RAW DNG's would not.

If you are recording ProRes files, an SDI monitor with a built-in waveform display, such as the new Marshall 5.6MD, would be very useful to correctly set the ISO. But if you are recording RAW DNG, the camera Zebra will correctly indicate the point of clipping of the sensor (and the SDI output will not).

What I am not yet clear on, is which (RAW sensor or SDI) is displayed with the Ultrascope.

Cheers.


You're correct.

So ISO is important for monitoring and for anytime you shoot ProRes and DNx, but it doesn't matter really for RAW. My understanding is that it is like RED, so ISO doesn't electronically boot the ISO.

When monitoring in Thunderbolt, you are monitoring RAW SENSOR, not what is on the HDSDI.

jb
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Felix Steinhardt

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Re: Zebra range and exposure question

PostMon Aug 27, 2012 2:56 am

Ok, so ISo is just metadata but I thought BMC said "native ISO is 800" and by that I thought ISO 800 is the sensitivity the sensor works with -> RAW
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John Brawley

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Re: Zebra range and exposure question

PostMon Aug 27, 2012 2:59 am

Felix Steinhardt wrote:Ok, so ISo is just metadata but I thought BMC said "native ISO is 800" and by that I thought ISO 800 is the sensitivity the sensor works with.


Correct.

ISO800 is the speed you get the optimum performance of the sensor in terms of dynamic range.

jb
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Felix Steinhardt

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Re: Zebra range and exposure question

PostMon Aug 27, 2012 3:01 am

All questions answered. Great forum! Thank you! :D
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Kristian Lam

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Re: Zebra range and exposure question

PostMon Aug 27, 2012 6:29 am

John Brawley wrote:
Noel Sterrett wrote:
Felix Steinhardt wrote:And by RAW you mean ISO 800, right?


When monitoring in Thunderbolt, you are monitoring RAW SENSOR, not what is on the HDSDI.

jb


Actually, the Thunderbolt out will be the same as the HD-SDI output.

Santeri Enstedt

Re: Zebra range and exposure question

PostTue Aug 28, 2012 9:26 am

I'm still a bit confused. How is ISO's less than 800 produced in the camera. Is it done optically or electronically?
If recording ProRes should I always set up the camera ISO800 and use ND's or is it worth using camera ISO's less than 800 in terms of picture quality?
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Felix Steinhardt

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Re: Zebra range and exposure question

PostTue Aug 28, 2012 11:58 am

Logically, it must be made electronically, so if something is just clipped at 800 it won´t recover at 400, 200. So these ISOs have less dynamic range and I wouldn´t use them.

Santeri Enstedt

Re: Zebra range and exposure question

PostTue Aug 28, 2012 2:30 pm

Thanks Felix!
So basically ISO's below 800 are always a compromise.
Great camera though!
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Peter J. DeCrescenzo

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Re: Zebra range and exposure question

PostTue Aug 28, 2012 4:49 pm

To the best of my knowledge, all digital cameras deliver their best dynamic range and signal-to-noise performance at one particular ISO/gain setting. Each camera has a different "sweet spot" ISO/gain point, depending on its sensor & internal processing design.

With each camera, setting the ISO/gain lower or higher than its sweet spot negatively affects image quality.

However, this knowledge is another tool in the DP's toolkit. For example, depending on what filtration you have available to you (e.g.: NDs), and the motion blur (shutter) and DOF (aperture & focal length) effects you desire for a particular scene, you may choose an ISO/gain setting which is not the camera's "ideal". That's usually alright, because art & business typically involves a series of compromises.

The current thinking appears to be that 800 ISO is the BMCC's "sweet spot". As more folks use the camera, it's possible that factoid may evolve a bit, or it may not. The important thing is to shoot, shoot, shoot and see what works best for you and your projects. Cheers.
Last edited by Peter J. DeCrescenzo on Tue Aug 28, 2012 9:09 pm, edited 1 time in total.
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Peter J. DeCrescenzo

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Re: Zebra range and exposure question

PostTue Aug 28, 2012 5:08 pm

John Brawley wrote:At the moment the zebra only goes down to 75%. The other thing to note is that it works of the sensor's LINEAR data. No gamma is applied to the zebra setting. That means when you set it to clipping, at 100%, it's basically showing you sensor clip IRRESPECTIVE of the ISO you might have set. This has more ramifications when shooting ProRes and DNx.

I know there are other exposure tools being looked at for down the road. For the moment Zebra works very well for me. There's so much DR that as long as I know what's clipping or near clipping, I know everything else is being captured. jb


You might not be able to answer these questions because of your NDA, or because the current firmware -- or, possibly, "certifications" -- simply don't allow it, but here goes:

(And my questions may not make sense since I'm still attempting to figure out how I might use the BMCC's zebra feature, at least at first.)

When shooting BMCC ProRes or DNxHD, given that the zebras are reporting sensor clipping, might it be possible for a user to determine a zebra value (say "75" or whatever) which consistently reports a fairly accurate relative "normal" exposure point for skin?

So, for example, through testing I may find that BMCC zebras at 75 on skin means the skin is 2 stops over (or whatever), so I know I have to adjust exposure settings accordingly?

If I remember correctly you've reported that when shooting RAW you set zebras at 100 and, given the BMCC's 13-stop latitude, "everything" falls into place exposure-wise other than very bright areas you've decided are OK to clip.

But when shooting ProRes/DNxHD, how might a DP use the BMCC's zebras to gauge typical exposure settings for skin? Or, is the DR/latitude in ProRes/DNxHD close enough to RAW that one sets exposure more or less the same way?

BTW, I've never used a light meter for shooting video and I'm not about to start. I have, however, used zebras in video cameras for decades.

Again, my questions might not make any sense, or can't be answered today. Either way, cheers!
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micklindquist

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Re: Zebra range and exposure question

PostWed Aug 29, 2012 12:04 pm

Any chance of dual zebras?

pls delete if this has already been posted
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Peter J. DeCrescenzo

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Re: Zebra range and exposure question

PostWed Aug 29, 2012 4:58 pm

If my question above ...
viewtopic.php?p=1659&sid=0184fc4c29b407ad263a73b5dd653df9#p1659

... makes sense & is answerable, it would great if one of the folks who have a BMCC in hand could answer. Or, if my question is misguided (!), I'd welcome learning in what way. :D Much appreciated.
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John Brawley

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Re: Zebra range and exposure question

PostThu Aug 30, 2012 4:44 am

Peter J. DeCrescenzo wrote:
John Brawley wrote:At the moment the zebra only goes down to 75%. The other thing to note is that it works of the sensor's LINEAR data. No gamma is applied to the zebra setting. That means when you set it to clipping, at 100%, it's basically showing you sensor clip IRRESPECTIVE of the ISO you might have set. This has more ramifications when shooting ProRes and DNx.

I know there are other exposure tools being looked at for down the road. For the moment Zebra works very well for me. There's so much DR that as long as I know what's clipping or near clipping, I know everything else is being captured. jb


You might not be able to answer these questions because of your NDA, or because the current firmware -- or, possibly, "certifications" -- simply don't allow it, but here goes:

(And my questions may not make sense since I'm still attempting to figure out how I might use the BMCC's zebra feature, at least at first.)

When shooting BMCC ProRes or DNxHD, given that the zebras are reporting sensor clipping, might it be possible for a user to determine a zebra value (say "75" or whatever) which consistently reports a fairly accurate relative "normal" exposure point for skin?

So, for example, through testing I may find that BMCC zebras at 75 on skin means the skin is 2 stops over (or whatever), so I know I have to adjust exposure settings accordingly?

If I remember correctly you've reported that when shooting RAW you set zebras at 100 and, given the BMCC's 13-stop latitude, "everything" falls into place exposure-wise other than very bright areas you've decided are OK to clip.

But when shooting ProRes/DNxHD, how might a DP use the BMCC's zebras to gauge typical exposure settings for skin? Or, is the DR/latitude in ProRes/DNxHD close enough to RAW that one sets exposure more or less the same way?

BTW, I've never used a light meter for shooting video and I'm not about to start. I have, however, used zebras in video cameras for decades.

Again, my questions might not make any sense, or can't be answered today. Either way, cheers!


I know that lower zebra numbers are on the cards, and here's certainly the place to ask for this.

The UPSIDE of having it work on linear sensor data is that the clipping indication is always absolute no matter what ISO you choose.

The downside is that because it's linear, I think in theory, the zebra would be at 50% to be 1 stop down from clipping. In otherwords, the 75-100% control is a very fine way of controlling highlights only. I don't think 75% is going to be low enough to give you a "traditional" way of exposing using Zebra for skin tone.

What you CAN do though is external monitoring. The Alphatron VF I'm using at the moment has user selectable Zebras and false colour. A lot of other on board monitors do the same.

jb
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John Brawley

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Re: Zebra range and exposure question

PostThu Aug 30, 2012 4:46 am

Santeri Enstedt wrote:I'm still a bit confused. How is ISO's less than 800 produced in the camera. Is it done optically or electronically?
If recording ProRes should I always set up the camera ISO800 and use ND's or is it worth using camera ISO's less than 800 in terms of picture quality?


When shooting ProRes or DNX, the sensor is still shooting at 800 but the CURVE is bent to *replicate* those ISO's. The tradeoff is that you reduce your dyanmic range. This is no different to the way other cameras work like RED.

So really to get the very most DR from this camera, aim to shoot at ISO800 and use ND filters to get you in the ball park of the Stop you want to shoot at. No matter if you're shooting ProRes, DNx or RAW.

jb
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Peter J. DeCrescenzo

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Re: Zebra range and exposure question

PostThu Aug 30, 2012 7:24 pm

Thanks for all your answers, JB!

I'm looking forward to testing & shooting with my BMCC, "soon" I hope! ;-)

Cheers.
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Denny Smith

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Re: Zebra range and exposure question

PostWed Aug 28, 2013 4:01 pm

Peter I was also "raised" on Zebras, could not always take a waveform meter in the field for ENG shoots, so Zebras did the trick. today, newer cameras lack the correct Zebra range to get IRE of 40 for skin tones, so, I Got and use the Zacuto EVF, it has two levels of Zebra at same time (you can set both 95 or 100 and 40 or whatever 2nd value you want). It also has false color, and the optical eyehole is great for glasses wearers.
Denny Smith
SHA Productions

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