Setting Correct Exposure on the BMPCC

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Lee Mackreath

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Setting Correct Exposure on the BMPCC

PostWed Oct 09, 2013 6:50 pm

I own a GH2 and use full manual control in video mode. When setting up a scene I will manually dial in my preferred aperture and shutter speed and then control the exposure using a variable nd filter. This is made easier by the GH2 as it tells me on the LCD how under/over exposed the scene is based on the metering mode I have chosen.

Obviously this kind of metering does not exist on the BMPCC but we do have the IRIS button!

I will get my BMPCC in a couple of weeks time. From my understanding I can pretty much follow the above procedure for setting the correct exposure on my BMPCC, the only difference is that the BMPCC does not have a metering mode as such so it will not tell me how over or under exposed the scene is. My thoughts are that I can kind of guess what I believe to be the best exposure for the scene (after I have fixed my aperture and shutter speed) by using the variable nd filter.

To correct or confirm if my own dialled in exposure is correct I assume in theory I could then press the IRIS button on the cam to see how the BMPCC exposes the scene and see how the aperture setting differs to my setting if at all?

Not sure if this method will work? Also how does the BMPCC meter a scene?..does it do a general meter for good exposure across the scene or is it centre weighted? Also does the percentage setting on the zebras have any direct correlation to how the BMPCC then choses the correct exposure for the scene?

Any help would be much appreciated!

thanks

Lee
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thebicyclecafe

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Re: Setting Correct Exposure on the BMPCC

PostWed Oct 09, 2013 7:13 pm

Lee,
Exposing with the BMPCC is very simple. Whether you use a lens that can be controlled by the camera, or not, it's the same procedure manually.
Set your zebras to 100%, set your aperture, shutter speed, ISO to what you want. Dial your vari ND to the point where no zebras appear (if you don't care about the areas that the zebras appear on, then don't worry about it). This is a simple way of ETTR- you are basically giving the sensor as much light as possible without clipping any highlights. Some folks have recommended either using 95% zebras or stopping down an additional 1/2 stop (if you're at 100% zebras), assuming you're shooting in ProRes (which is all we have in the BMPCC now anyway). As an aside, I've been shooting at 100% zebras and don't notice any issues with overexposure.

You would then pull the footage back down in post. By shooting this way in film mode, you maximize DR. If you are shooting in video mode, the camera will pull the footage down for you.

Now, assuming you are using an "iris-able" lens, for example a Pany or Oly m4/3 lens:
The camera does the same exact thing in film mode- when you hit iris, it will stop the lens as far down so as to not clip any highlights. If you were to already dial down your ND just to the point that no zebras appears, clicking the iris button will likely show no changes to aperture. In video mode, the camera actually does take an exposure average, so you are likely to see the camera stop down a bit, assuming the manual method yielded an ETTR scenario- just be forewarned that you are giving up some DR by shooting via auto-exposure in video mode.

The same idea applies whether or not you are using a vari-ND, you would stop the lens down instead of using the vari-ND, I just tailored my explanation to your described shooting method. HTH!
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Enrico Trippa

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Re: Setting Correct Exposure on the BMPCC

PostWed Oct 09, 2013 8:55 pm

Excellent explanation!
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Aaron Green

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Re: Setting Correct Exposure on the BMPCC

PostWed Oct 09, 2013 9:08 pm

I've found that ETTR doesn't work as well with Pro Res. It's fine with RAW but it becomes a little too noisy in the shadows with Pro Res. Maybe set zebras to 90 or so.
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thebicyclecafe

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Re: Setting Correct Exposure on the BMPCC

PostWed Oct 09, 2013 9:23 pm

AaronChicago wrote:I've found that ETTR doesn't work as well with Pro Res. It's fine with RAW but it becomes a little too noisy in the shadows with Pro Res. Maybe set zebras to 90 or so.

I haven't noticed that... what you're noticing actually sounds a bit counter-intuitive to me since the footage is pulled in post-processing, not pushed. One would expect to get less, not more shadow noise when an image is pulled.
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Kholi Hicks

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Re: Setting Correct Exposure on the BMPCC

PostWed Oct 09, 2013 10:44 pm

The method that you're describing is for shooting RAW on the 2.5K, and sometimes isn't the best way to shoot.

Doing this in ProRes may put your middle grey in a place where you do not want it.

What's likely happening in AaronChicago's case: He may be trying to save highlights that are forcing his image into the lower mids/shadows, and trying to stretch what's been compressed in a LOG curve exposes noise.
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thebicyclecafe

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Re: Setting Correct Exposure on the BMPCC

PostWed Oct 09, 2013 11:13 pm

Khoi, agreed- however in the absence of a good light meter and a grey card, I think it's the next best option. If you're more conservative you can set zebras at 90-95%. But I find that until RAW arrives... ProRes actually works quite well and has sufficient latitude for most scenes shot this way. Essentially, that is how the so-called auto exposure works in film mode.
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DanAbrams

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Re: Setting Correct Exposure on the BMPCC

PostThu Oct 10, 2013 1:23 am

Agreed, you really need to use a conservative ettr or a meter.

I got done in using ettr on a shoot this week and spent the whole day in resolve trying to fix it today. Ugh.
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Lee Mackreath

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Re: Setting Correct Exposure on the BMPCC

PostThu Oct 10, 2013 6:36 am

Sorry I am bit confused about the concern over using 100% zebras and overexposing shots?...surely setting your zebras at 100% means you will only be losing the most blown out of highlights and the topend and therefore be closer to overexposing than underexposing?

I thought that being conservative at around 90% zebras would mean the opposite...that you are more likely to make sure nothing gets blown out and be in position where you tend to under rather than overexpose?
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Lee Mackreath

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Re: Setting Correct Exposure on the BMPCC

PostThu Oct 10, 2013 7:47 am

Also, does the dynamic range option you set on your display affect the zebras?

Obviously there is the dynamic range setting in the recorder settings that I would set to film mode and not video...but I have read it is better to then have the display actual display the dynamic range in video mode...if you do this does the zebra levels change compared to if you used film mode in the display options?
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Mac Jaeger

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Re: Setting Correct Exposure on the BMPCC

PostThu Oct 10, 2013 8:31 am

100% zebras doesn't always guarantee that nothing clips. The zebras are based on combined values for all colors, yet if you have - say - a very bright, saturated red (think: red neon lights) it is possible that the red clips even though the combined value of red, green and blue doesn't exceed 100%. So if you have a colored highlight you could still get clipped data even though the zebras don't warn you, that's why it is prudent to stop down a little, or just set the zebras to 95% or even 90% and expose until there are no zebras in the picture.
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Lee Mackreath

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Re: Setting Correct Exposure on the BMPCC

PostThu Oct 10, 2013 8:38 am

Thanks for the explanation...might me prudent to shoot at around 90% then.

I assume setting the display to ether film or video mode does not affect the zebra levels in any way regardless of the fact you have set the recording option to film?

I guess having the option of setting the display to video just allows the shooter to see what the final image would look like if you were to apply a 709 LUT to the shot in its current exposed state.

I imagine it is hard to correctly guess how you want your exposed scene to look in film dislay mode...even though that is how the pro res file will look once you put it into your NLE?
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thebicyclecafe

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Re: Setting Correct Exposure on the BMPCC

PostThu Oct 10, 2013 6:14 pm

Hi Lee,
Here's where shooting with the zebras can get a bit more confusing since you can underexpose or overexposed by shooting this way, so that's where some judgment comes into play. It all depends on the variability of EVs in a particular scene.
Say you are shooting a high contrast scene, ie a person against a heavily backlit sunset scene. By preserving those highlights, you will have to stop down significantly, thereby underexposing your subject in the foreground. In this scenario, you'd want to expose as far to the right as possible, with 100% zebras, without clipping in the background (assuming you want to preserve the sky). It's harder to recover clipped highlights than it is to push the shadows.

Now say you're shooting a grey card, or a flat, evenly lit scene with few highlights. You would have to open up the lens quite a bit to get clipping, so you would be overexposing the entire scene.

In this scenario you would want to shoot maybe 90% zebras, since ProRes has less latitude than RAW, so you don't have to pull the exposure down too much in post. You do still want to ETTR somewhat though, since you still get the benefit in this case.

So, in my experience so far, 100% zebras yields a good exposure in many outdoor scenes, since you often have high con situations. In others, I have to use my judgment and change settings accordingly. I have shot at 90-95% zebras in flatter lighting an the image looks great.

Don't worry too much about what the image looks like on the LCD anyway, too many variables factor into how it looks on the LCD, before you can even judge exposure on it...
When you get your cam, test shoot in a variety of lighting scenarios, using different zebra settings. Take good notes, then edit the image to your liking in your NLE.... Compare, and adjust your shooing habits accordingly. There is a learning curve, but it's not terribly steep, the camera is easy to learn to use. When RAW comes and you want to use it, there will be some adjustment in how you shoot. For now ProRes has so much headroom compared to consumer codecs, I think you will be very happy with the results you get.
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Occular

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Re: Setting Correct Exposure on the BMPCC

PostThu Feb 06, 2014 10:42 am

Just want to add my tuppence worth (slightly late).

If shooting ProRes, blindly using 100% zebras and ETTR doesn't always give you an optimal result, so I do recommend using (e.g.) 90 or 95% zebras sometimes depending on the lighting in your scene.

Example: I shot an outdoor scene in bright sunlight using 100% zebra to ETTR. Nothing was clipped, *but* the sky which was bright blue and on the right edge of the histogram was showing terribly obvious banding - there were about 6 bands of colour in the sky, with very obvious delineations, unless I pushed that detail until it was very high up.

I've recently acquired a spot meter (the Sekonic 758 Cine) to help better judge exposure choices in conditions like this.
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tvsterling

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Re: Setting Correct Exposure on the BMPCC

PostFri Feb 07, 2014 4:27 am

Back to The Future. I'm going to have to dust off my Spectra-Combi & get a new battery. Now that video is evolving into the same lattitude range as ECN the older exposure strategies will come back from the shadows (no pun intended).
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MikeMeagher

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Re: Setting Correct Exposure on the BMPCC

PostFri Feb 07, 2014 5:16 am

Learning how to expose and shoot the BMPCC is giving me a "deja-vu" moment, of my still photography days.. when I used to dabble in the "zone" system.

The concepts of the zone system were basic:, expose for the shadows, and develop for the highlights. That was the basic core of it. Someone shooting using the Zone system would have to first see in the minds eye the desired end product, then in the field shoot the camera a certain way, shoot it to a certain zone setting to best achieve that desired result.. but the work wasn't done, then we had to in the darkroom develop and print to that zone to achieve the end result.

The proper exposure of a "cinema" camera is akin to shooting film using the zone system. The exposure used in the camera must take into account the intended result, and the adjustments that you plan to do in Post production.

I have to give credit to where credit is due, but I found some very good articles on the RED website about exposure setting, exposure theory, to ETTR or not. I believe this advice applies also to the BM line of cameras. The exact techniques are different, as the tools are different.. but you'll get the idea.

One quote that I read at the RED website which I believe hits the mark on exposure strategy:

"Some advocate a strategy called “expose to the right” (ETTR), whose central principle is to record as much light as possible without clipping—causing the histogram to appear shifted to the far right. While this approach works well with stills photography, it greatly increases the likelihood of clipped highlights with video footage, since lighting conditions are often more dynamic.

Furthermore, ETTR can be misleading since the live histogram doesn’t represent raw image data. An ETTR strategy that doesn’t also pay attention to the goal posts therefore runs a high risk of overexposure—and increasingly so at lower ISO settings. Instead of recording as much light as possible, we instead encourage only recording as much light as necessary to meet one’s goals for image noise, but not necessarily any more than that—all while paying attention to the goal posts and traffic lights in addition to the histogram."

In other words, make use of both some sort of exposure metering tool (their cameras have tools called Goal Posts and Traffic Lights for gauging over, under, exposed areas)... and to also make use of zebras.. and to keep in mind your intended results and to in post make the required adjustments, to get the end result.. there is no single fail catch all method.
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MarcusWolschon

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Re: Setting Correct Exposure on the BMPCC

PostFri Feb 07, 2014 10:56 am

Be careful with the IRIS button.
It doesn't care for average brightness but just makes sure the brightest, single pixel is still not clipped.
So a dark scene with a single point of light will be exposed for the light, leaving the scene mostly black.
I found the iris button to be useless.
However manually setting iris using IRIS+UP/DOWN breaks your fingers.
You cannot do this button combination with the hand that holds the camera but need both hands
Same for FOCUS+UP/DOWN .
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lee patterson

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Re: Setting Correct Exposure on the BMPCC

PostMon Mar 03, 2014 1:05 am

I have just come across this Dave Dugdale video where he shares a methodology given to him by a colourist. Apologies if this has been covered before, it was new to me. Anyone have any further thoughts? Be really interested to hear the community's opinion on this one. Thanks
http://www.learningdslrvideo.com/bmpcc- ... -tutorial/
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tvsterling

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Re: Setting Correct Exposure on the BMPCC

PostMon Mar 03, 2014 3:32 am

It's back to the future. As the electronic image becomes more like the chemical image (in things like latitude/ dynamic range) the old exposure techniques will make a comeback. I already been there & done that. Suggest serious people get a good exposure meter & review the old ways such as the zone system. I am going to try & prove this by experiment but my gut tells me you need to expose for the darkest shadows you want detail in & grade for the best highlight rendering you can get depending on where & how you are going to distribute. Back in the day we did this in film except we worked the developer instead of grading. I like my Spectra Combi meter since it reads reflected, incident or a combination of the two. Pick up some books on exposure & developing techniques; I think lots of the concepts will cross over. I am SO GLAD to see the crushed black shadows & the blown out highlights of early analog video go away. Like everybody else I had to go video & put the film cameras on the shelf. Film is gone & believe me it had plenty of faults of it's own but now the actual beauty of the video image is really getting there. Good times indeed. One last thought; In the olden days we avoided color lighting crossovers like the plague. Film gives really ugly results when you mix light sources (like Daylight & 3200K) so we had to be careful. Since video has always handled crossover lighting much better it is easy to get sloppy on this point. DON'T DO IT. Care in crafting the lighting will yield many, many dividends. Avoid color crossovers & get much prettier footage.
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Uli Plank

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Re: Setting Correct Exposure on the BMPCC

PostMon Mar 03, 2014 7:21 am

I only wished the iris button would work somehow like the 'traffic lights' in RED cameras. They neglect very small overexposed areas (like a small light source or shiny reflection in the frame) and only warn you if a considerable number of photocells is overexposed.
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Chris Keller

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Re: AW: Setting Correct Exposure on the BMPCC

PostTue Mar 24, 2015 6:48 pm

I'm relatively new to the BMPCC, and I'm a total newbie when it comes to exposing using false color (I have the Zacuto EVF Pro). Are there tutorials somewhere on the internet, both video or text, that deal with that subject, exposing with false color function?

Thanks very much in advance!
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Anna Petrova

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Re: Setting Correct Exposure on the BMPCC

PostTue Mar 24, 2015 9:55 pm

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Lee Gauthier

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Re: Setting Correct Exposure on the BMPCC

PostTue Mar 24, 2015 10:46 pm

ETTR poses a problem for narrative filmmaking, in that it's easy to end up with mismatched shots. A wide shot and a close-up may have very different contrast ratios, while still having the main point of interest in the same light.

Get a meter, if only to match your ratios.
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Chris Wallace

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Re: Setting Correct Exposure on the BMPCC

PostTue Jul 14, 2015 8:23 am

Hi, I just bought a used BMPCC but I'm not sure I understand how to ETTR. My Zebras are set to 100% in the menu and if I adjust the settings (aperture, shutter speed, ISO) so there's no zebras on the display the image gets dark and not bright as discribed.

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