How to (over-)expose correctly?

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John Waldorff

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How to (over-)expose correctly?

PostSun Nov 25, 2012 11:58 pm

Hello,

As someone who is among the crowd that has not received the camera yet.. I can rely only on other people's opinions.

One common opinion seems to be:
When shooting RAW dynamic range is best preserved when over-exposing.

However, the monitor shows only a fraction of the dynamic range and ISO settings are taken into account, so you cannot rely that you see everything.
Instead it makes sense to set the ISO lower, so the zebras show earlier and the overall picture looks more natural (although actually overexposing 3 (?) stops).

So how you work with the camera?
-) Using histogram (does it have one?) and adjusting iris and ND setting so histogram goes fairly to the right.
-) Low ISO to actually see the zebras for sharp focus
-) Double pad the screen to check focus
-) Jump back and forth between these settings is easy?

Cheers
Last edited by John Waldorff on Tue Nov 27, 2012 1:57 am, edited 1 time in total.
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Margus Voll

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Re: How to (over-)expose correctly?

PostMon Nov 26, 2012 7:48 am

I think it has been covered earlier that you should exposure almost 100 % of zebras maybe a bit under.

Have not seen on camera results myself but i recon if you would want to be super safe 95% would be good.

I may be mistaken here also but that is the feel i have until now by other posts.
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adamroberts

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Re: How to (over-)expose correctly?

PostMon Nov 26, 2012 8:10 am

John it may be a language thing but Zebras has nothing to do with focus. It only shows exposure.

The Zebras on the BMCC display are based on the RAW image. If you use Zebras on an external monitor it will be based on the signal coming out of the HD-SDI which would be in Video or Film gamma and at the ISO you choose.

When shooting RAW you should expose so you see no zebras on your highlights on the BMCC screen. This would mean no highlights are clipped in the RAW file. For ProRes you would be better off checking exposure on an external display tho or do some tests with the various Zebra and ISO settings to find you perfect exposure feedback
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John Waldorff

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Re: How to (over-)expose correctly?

PostMon Nov 26, 2012 1:58 pm

Ok, thank you.
That makes sense =)
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Jason Hinkle

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Re: How to (over-)expose correctly?

PostMon Nov 26, 2012 11:33 pm

I usually try to go for no zebra lines, but I've thought that, depending on the shot and especially in extreme contrast lighting, that sometimes a few zebra lines may be necessary. But you have to realize that you're blowing out in those spots.

How far would you guys go with underexposing your shot in order to not have any zebra lines in RAW? For example - a reflection of the sun on a shiny car or somebody's forehead, etc..? (Also assuming you don't have 100% control of the lighting in order to get rid of the spot - for example a live event or something)
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Nick Bedford

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Re: How to (over-)expose correctly?

PostTue Nov 27, 2012 5:35 am

It's an artistic choice but the more cinematography I study, the more I see the "protect the highlights and see what the shadows do" as the common style of exposure. And when you need to push the exposure against something like an outside sky, it should be almost completely overexposed so that you're not "stumbling" in and out of clipping, if you get my meaning?

But it's up to you as the DP to make the choice. Or you can try to elevate the shadows with light to reduce the scene's dynamic range.

The main goal is to not bring attention to the clipped areas. Saving a clipped image can often result in mucky fringed edges and ugly colours if you're not careful.
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Fabián Matas

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Re: How to (over-)expose correctly?

PostWed Nov 28, 2012 11:59 am

Since the DI appear in action is more, take the full info and go in post. RAW is just the DI next step.
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John Waldorff

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Re: How to (over-)expose correctly?

PostTue Dec 04, 2012 11:03 pm

But Marco Solorio from onerivermedia said that it is better to overexpose. John Brawley also wrote about that.

Hmm but what did they mean? 20% zebra, or 40%?
If you go for no zebra, then it is not really overexposed.

Cheers
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Margus Voll

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Re: How to (over-)expose correctly?

PostWed Dec 05, 2012 7:25 am

then it would be exposed correctly and not under exposed.
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rick.lang

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Re: How to (over-)expose correctly?

PostWed Dec 05, 2012 3:06 pm

John Waldorff wrote:But Marco Solorio from onerivermedia said that it is better to overexpose. John Brawley also wrote about that.

Hmm but what did they mean? 20% zebra, or 40%?
If you go for no zebra, then it is not really overexposed.

Cheers


No zebra showing would indicate nothing is overexposed. The darkest content may actually be underexposed when you "protect the highlights." You might typically achieve that setting zebras at 100% or 95% in the BMCC. The lowest setting for zebras is 75% in the BMCC if I recall correctly. if you used that setting you would likely be crushing the blacks and reducing your dynamic range I think. Something slightly less than 100% zebras may be desired though if the scene is very bright such as shooting snow on a sunny day. Okay, chilly example; better, shooting on the sunlit beach at mid-day... You might want to have a little extra safety margin as some snow or water reflection is going to be brighter than you expected.

If you want to expose so that you get more detail and less noise in the blacks, then you may well have zebras for the highlights. John has mentioned that in some scenes, you would intentionally clip the highlights in a correct exposure for most of the shot, for example at the extreme, if you shoot someone arc welding, you are going to intentionally clip the arc but the rest of the shot will be exposed correctly.

My point is showing some zebras, with the camera set at 100% zebras, isn't necessarily an overexposed shot, just a choice you make depending on what you want to expose for and where clipping is allowed. In a typical shot, given the large dynamic range of the camera, you would want to expose just under the point zebras show.
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John Waldorff

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Re: How to (over-)expose correctly?

PostThu Dec 06, 2012 1:40 am

Great advice on this one. :)
Thanks.
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Bill Rich

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Re: How to (over-)expose correctly?

PostThu Dec 06, 2012 1:53 am

In Marco's last video I believe he said he sets his zebras to 100% then exposes until he hits 100%.. Please correct me if I'm wrong Marco
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John Brawley

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Re: How to (over-)expose correctly?

PostThu Dec 06, 2012 8:10 am

It's not overexposing.

You're simply "exposing to the right".

This means you're not doing what works best with just about every other video camera on the market.

For years it's been standard practice to under expose your shots to protect your highlights and then "lift" the grade to get the image back to normal.

This is not the best way to get the most from this camera. It really doesn't like being underexposed. It wants a "fat" negative. Use zebras @100% to decide where to set your clipping point (or even have everything sit just below clipping).

JB.
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chauffeurdevan

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Re: How to (over-)expose correctly?

PostThu Dec 06, 2012 1:17 pm

I am really not a fan of zebra.

Zebra is working only on near white value, but doesn't prevent channels from clipping yielding too much to flat, color distortion and low saturation color on the highlight side (eg. sky).

As rgb space is a double conic space, meaning that shadow value and highlight value have lower saturation than medium value.

When you have a sky a little bit overexposed - that happen a lot by zebra metering - your blue channel will clip, and the brighter it get, the higher the green and red gets.

The clipped blue yield to a flat colors. As the green and red gets brighter, saturation of the final color decrease as saturation is the result of difference between channels.

As it gets really bright, either the red or green channel will clip. This will slowlo shift the color to pink/purple if the red channel clip first. Or yellower if the green channel clip first.


I am a strong advocate for color histogram metering. You are able to judge the of the entire spectrum of the entire image - even in bright snowy day.
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Marco Solorio

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Re: How to (over-)expose correctly?

PostFri Dec 07, 2012 1:58 am

I totally echo John's statements. IMO Jocelyn, you absolutely need to shoot with 100% zebras in RAW, even if you're not a fan of zebras in the traditional sense. It's much different than shooting regular video in any other camera, where zebras can sometimes "get in the way". At 100%, you shouldn't really see them (right before the point of clipping), unless you're intentionally allowing some clipping to occur in certain areas (like the very center of a car's headlight for example). So with this in mind, it shouldn't be distracting, and more so as a valuable (invaluable) alert. If you shoot RAW in the same manner as shooting regular video, you'll miss out on a ton of image data you can otherwise use to your advantage.

In my recent webinar at Moviola, I go over how to expose for RAW, and how some shots look like they're way over exposed, but in reality are maintaining the highest degree of latitude and signal-to-noise ratio in the shot. I show this with visual examples to make it clear to understand. Doing this helps protect shadow areas from getting too noisy, while still allowing for highlight protection.

http://www.moviola.com/on-demand/first- ... ema-camera

Hope this helps.
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andrewgooi

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Re: How to (over-)expose correctly?

PostThu Mar 07, 2013 10:47 pm

If one were to expose to the right for the BMCC say for a scene with faces involved, do I grade the footage to make sure the skin tone shows up right - and everything else should fall into place?

Ultimately, I am wondering if ETTR will help with skin tones.

Thanks!
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Randy Walters

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Re: How to (over-)expose correctly?

PostFri Mar 08, 2013 4:02 am

Jocelyn, I believe I remember John Brawley saying that the zebras clip if *any* of the individual RGB channels touch or exceed whatever value the camera is set for. So on the BMCC, the zebras actually are a dependable means of avoiding clipping.

Sorry I don't know where to find the specific reference.
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Darryl Gregory

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Re: How to (over-)expose correctly?

PostFri Mar 08, 2013 5:11 am

andrewgooi wrote:If one were to expose to the right for the BMCC say for a scene with faces involved, do I grade the footage to make sure the skin tone shows up right - and everything else should fall into place?

Ultimately, I am wondering if ETTR will help with skin tones.

Thanks!



ETTR: Advantages include greater tonal range in dark areas, greater signal-to-noise ratio (SNR), fuller use of the colour gamut and greater latitude during post-production.
Last edited by Darryl Gregory on Fri Mar 08, 2013 5:28 pm, edited 1 time in total.
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Brad Ballew

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Re: How to (over-)expose correctly?

PostFri Mar 08, 2013 1:43 pm

Randy Walters wrote:Jocelyn, I believe I remember John Brawley saying that the zebras clip if *any* of the individual RGB channels touch or exceed whatever value the camera is set for. So on the BMCC, the zebras actually are a dependable means of avoiding clipping.

Sorry I don't know where to find the specific reference.


I am glad I found this thread. For some reason I had the idea that because I was shooting raw that there was a little leeway past 100% zebras. I have no idea why I thought this, it seems a bit silly in retrospect. I hadn't really had time to really test but I always wondered about it. I did a shoot out at Dallas Heritage Village the other day and it was particularly bright and I didn't have an ND with me for some reason. There were several times I had zebras in the sky that I thought I might be able to pull back... nope. Just white. Between that experience and this thread I feel like I can move forward and shoot properly with this camera.

As another post indicated, it does take some time to get a feel for how best to shoot with the camera. I have shot run n gun on DSLRs for so long that I feel like I wasn't really becoming a better cinematographer. Getting this camera has really motivated my to work harder at refining my knowledge and skill in the art of cinematography. Hell I even just signed up over at the Roger Deakins forum. How cool is that guy to set up a forum and answer people's questions on a regular basis. The guy has got class.
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Noel Sterrett

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Re: How to (over-)expose correctly?

PostFri Mar 08, 2013 2:08 pm

The thing to consider with ETTR is that the linear/log conversion adds bits at the low end at the expense of the high end. The log format works well unless the most important parts of the image lie at the high end.

Cheers.
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rick.lang

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Re: How to (over-)expose correctly?

PostFri Mar 08, 2013 10:27 pm

Noel Sterrett wrote:The thing to consider with ETTR is that the linear/log conversion adds bits at the low end at the expense of the high end. The log format works well unless the most important parts of the image lie at the high end.

Cheers.


In that situation where you want to retain even more of the highlights, would it make sense to set zebras at 90% or 95% and sacrifice a little of the shadows?

Rick Lang
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danap

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Re: How to (over-)expose correctly?

PostSat Mar 09, 2013 7:14 am

And what does "percent" mean in term of zebra: linear or log percentage? EV ? 1 percent =1.3 stop?
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andrewgooi

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Re: How to (over-)expose correctly?

PostSat Mar 16, 2013 5:25 pm

ETTR applies only to RAW filming right - could you do the same with ProRes?
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Trevor Roach

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Re: How to (over-)expose correctly?

PostSat Mar 16, 2013 11:27 pm

andrewgooi wrote:ETTR applies only to RAW filming right - could you do the same with ProRes?



I've only had the camera for 5 days, but from my (short) experience... ETTR in just about any situation no matter what format. Having the zebras on 100% is key, as others have said. I would also highly suggest getting some good NDs or Grad filters. As great as the dynamic range is on this camera, if you want to get even more out of a sky, for example, you need some NDs or else you'll be at f22 and still maybe seeing some zebras.

I believe JB was using an ND6 even for some interior scenes in his "Afterglow" piece. Camera loves light, so you want to pump a bunch in, but if you still want some DOF, adding an ND will give you the best of both worlds.
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Trevr Merchant

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Re: How to (over-)expose correctly?

PostMon Mar 18, 2013 1:40 am

No one has mentioned it on this thread yet so I will bring it up.

Has anyone used an incident meter with this camera?
Shooting with it today, I was metering at an f/9 but getting proper exposure (post-grade) at an f/4.

I know this is in line with the whole exposing to the right trend but I am just curious if there is a standard overexposure compensation formula someone has come up with?

Or should I just "expose to the right" at my own disgression?

I'm primarily shooting ProRes so the exposure needs to be solid every time.

Thanks,
Trevr Merchant
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Frank Glencairn

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Re: How to (over-)expose correctly?

PostMon Mar 18, 2013 9:21 am

Light meters where made for film and film reacts different than the BMC sensor (especially at raw), which renders them IMHO useless for exposure. But they are pretty good for checking your levels - which may be more important anyway.

Personally I prefer to check my levels at a glance of the false color function of my TVLogic monitor, which I find more effective and faster - especially I can dial in my levels in realtime, by having someone moving lights or changing intensity. But there is nothing wrong with using a light meter for that - for exposure, not really.
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Sam Joos

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Re: How to (over-)expose correctly?

PostFri Mar 29, 2013 9:27 pm

Hey guys,

Ive been doing test shoots since I got my camera two days ago and had a couple issues, Im am shooting outside, partly cloudy in Raw, iso at 800, no ND and stopped down to f22.. I do see very little zebra pantern in the sky which are set at 100%.. However my subject who is riding a skateboard has a heavy amount of noise on them when looking back at the files in Finder and Resolve. Is it safe to say I need to really blow out the sky to get a clean image on my subject?
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Steve Jakubowski

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Re: How to (over-)expose correctly?

PostFri Mar 29, 2013 10:11 pm

joos wrote:Hey guys,

Ive been doing test shoots since I got my camera two days ago and had a couple issues, Im am shooting outside, partly cloudy in Raw, iso at 800, no ND and stopped down to f22.. I do see very little zebra pantern in the sky which are set at 100%.. However my subject who is riding a skateboard has a heavy amount of noise on them when looking back at the files in Finder and Resolve. Is it safe to say I need to really blow out the sky to get a clean image on my subject?

iso 800 sounds a bit high, try the lower end of the range IMHO, with Zebras set to 100% expose untill you get zebras showing on the screen the back off a bit until they disaspear.
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Sam Joos

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Re: How to (over-)expose correctly?

PostFri Mar 29, 2013 11:37 pm

Steve Jakubowski wrote:iso 800 sounds a bit high, try the lower end of the range IMHO, with Zebras set to 100% expose untill you get zebras showing on the screen the back off a bit until they disaspear.


The reason I was going 800 is to stay true to the native iso of the camera and to get what I thought the proper exposure seen through the monitor. It does make since I guess in that bright of a situation for peaking reasons to drop the iso for the sake of accurate zebras, but then I feel I may be to overexposed if 200 and 400 isnt the native iso. Again I am shooting raw, not baked in prores or DNxHD.
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Felix Steinhardt

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Re: How to (over-)expose correctly?

PostSat Mar 30, 2013 1:09 am

I made a quick test yesterday how to overexpose in low key scenes.

make sure to download the original file!

Edit: I just tested the BMCCs highlight rolloff. Firstly I wasn´t able to use my "standard test" (standing lamp that illuminates the ceiling). Where my FS700 shows 100 % zebras everywhere the BMCC just faintly shows zebras in the bulb itself...What a camera!

The rolloff is the best I´ve seen yet. It´s much better than the FS700s and even a lot better than my Nikon D7000 RAW photos! The Nikon stands no chance at all. I´ll post some examples later.

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