Exposing with BMPCC

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v493ymb98

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Exposing with BMPCC

PostTue Oct 02, 2018 2:58 pm

Hi folks, I've got a question about exposure on BMPCC,

I just recently shot some interviews with BMPCC amd Zeiss 21mm lens, and set the highlights of the faces so that 75% zebra just gave some stripes.

80% gave no zebras on the subject.

Now I see that the highlights of the faces have clipped. Can you advise me, where did I screw it up?
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Howard Roll

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Re: Exposing with BMPCC

PostWed Oct 03, 2018 3:32 pm

Shooting at low ISO will do that. Leave the ISO at 800 and shoot away, there are no rewards for shooting low ISO on the Pocket.
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v493ymb98

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Re: Exposing with BMPCC

PostWed Oct 03, 2018 7:34 pm

Howard Roll wrote:Shooting at low ISO will do that. Leave the ISO at 800 and shoot away, there are no rewards for shooting low ISO on the Pocket.

Thanks for this information! However, I did shoot with ISO 800, or even 1600. I was using ambient light indoors, so I could not shoot with low ISO. So what could be another cause for the clipping? Hmm.
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Brad Hurley

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Re: Exposing with BMPCC

PostThu Oct 04, 2018 12:27 am

I'm far from an expert on this, but from what I've read the zebras display a sum of all color channel levels, which means that a particular color channel could be blown out even if you don't see zebras. Most of the advice I've seen says to set zebras at around 70% for caucasian faces, but that's obviously a very rough rule of thumb.
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Mike C Bonner

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Re: Exposing with BMPCC

PostThu Oct 04, 2018 6:52 am

Are you shooting film or video dynamic range?

What you are trying to do will only work if you are using the video range, where 75% will be 75% of rec709 range.

When you shoot film it displays the zebras as 75% of the entire 13 stops of dymamic range.

It sounds like you put the skin tones not at 75% rec709, but rather more like 110%, and is therefore overexposed. You can do the way described, but when you flip back to film mode you won’t see the zebras where you’d expect them.
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v493ymb98

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Re: Exposing with BMPCC

PostThu Oct 04, 2018 7:02 am

Thanks!

Muke, that's what I was suspecting. Too bad the manual doesn't guide me in this subject. I really did nit know, but it seemed like the thing that happens with slog dr's f.ex.

I was able to rescue them with some comor correction trickery so that they're nit really visible, but it would ve nice if the iperation manual would state that the zebras don't mean anything when shioting in film mode.
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Howard Roll

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Re: Exposing with BMPCC

PostThu Oct 04, 2018 7:21 am

My second guess would be that you’re using a lut that isn’t expecting your 3 stop ettr on the face and is blowing out skin tones.
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v493ymb98

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Re: Exposing with BMPCC

PostThu Oct 04, 2018 10:36 am

Brad Hurley wrote:I'm far from an expert on this, but from what I've read the zebras display a sum of all color channel levels, which means that a particular color channel could be blown out even if you don't see zebras. Most of the advice I've seen says to set zebras at around 70% for caucasian faces, but that's obviously a very rough rule of thumb.

Yes I was looking forward to correcting it in post roughly, and setting the absolute highlisghts to 75% so that the not-so-bright areas of the face would be under 75% zebra aperture, which shoulf give them roughly proper exposure to work with later. My WB was off, but it didn't matter that much in this case.

Mike C Bonner wrote:Are you shooting film or video dynamic range?

What you are trying to do will only work if you are using the video range, where 75% will be 75% of rec709 range.

When you shoot film it displays the zebras as 75% of the entire 13 stops of dymamic range.

It sounds like you put the skin tones not at 75% rec709, but rather more like 110%, and is therefore overexposed. You can do the way described, but when you flip back to film mode you won’t see the zebras where you’d expect them.


My reply to you might still be pending, since I'm a new user, but I'm gonna give a better one now. I was talking about this with a friend, and he speculated it might be similar issue than what could happen with Sony's slog gamma curve. I could not predict how the film dynamic range relates to zebras and everything, since there was no information available about it in the manual. Fine, it might be my lack of expertise, but still giving users basic information about how to expose with a given DR setting with in-camera tools would be polite.

Howard Roll wrote:My second guess would be that you’re using a lut that isn’t expecting your 3 stop ettr on the face and is blowing out skin tones.


Hmm, I just loaded the clip into Premiere and then Resolve, and they both gave the same result without any color adjusting present. Thus, lut plays no role in here currently, although I might be able to compensate with one.

Anyhow, I was able to pull down the highlights in Resolve so that it doesn't look too bad. I think what happened was probably what Mike wrote, I used zebras inappropriately in film dynamic range mode. For my defense, I gotta say the manual could be clear about it. It only states that "setting the zebra to 100% shows which areas are clipped", and goes no further into the subject. Obviously, in this case, that statement gave me wrong impression about the function.
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Denny Smith

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Re: Exposing with BMPCC

PostThu Oct 04, 2018 5:11 pm

Yes, 100-percent shows absolute clipping. But 80 or 90 percent could still have one color channel clipping and not the other two.

Zebras are aonly an approximation at best. For better accucracy you need a waveform scope with RGB Parsde, showing each color channel individually or in different colors to see what is really happening. I think You can check this in Resolve with your original file, to see if one colors did clip.

False color is a better way to check exposure, but you need a monitor thst supports this, and also waveform scopes. The BMPCC only has the histogram, whichmis more of a still camera tool.

That said, I had good luck keeping rh Pocket camera at ISO 800, setting Zebra to 90 percent (to cover single color channel clipping) and exposing the scene to keep by brightest bit I want to have details in from displaying zebra, and subsequently clipping. Skin tones, I metered with a Cine light meter, and also used a waveform monitor.

If I had a Pocket today, I would be putting a SmallHD Focus on it, with the BMPCC dummy battery kit, and use it with rhe Pixket Camera, thusmgetting Flase Color and Scopes with RGB Parade. I found the Pocket Camera, small back monitor next to useless, it was so low in resolution and hard to see.
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v493ymb98

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Re: Exposing with BMPCC

PostSat Oct 06, 2018 7:54 pm

Denny Smith wrote:Yes, 100-percent shows absolute clipping. But 80 or 90 percent could still have one color channel clipping and not the other two.

Zebras are aonly an approximation at best. For better accucracy you need a waveform scope with RGB Parsde, showing each color channel individually or in different colors to see what is really happening. I think You can check this in Resolve with your original file, to see if one colors did clip.

False color is a better way to check exposure, but you need a monitor thst supports this, and also waveform scopes. The BMPCC only has the histogram, whichmis more of a still camera tool.

That said, I had good luck keeping rh Pocket camera at ISO 800, setting Zebra to 90 percent (to cover single color channel clipping) and exposing the scene to keep by brightest bit I want to have details in from displaying zebra, and subsequently clipping. Skin tones, I metered with a Cine light meter, and also used a waveform monitor.

If I had a Pocket today, I would be putting a SmallHD Focus on it, with the BMPCC dummy battery kit, and use it with rhe Pixket Camera, thusmgetting Flase Color and Scopes with RGB Parade. I found the Pocket Camera, small back monitor next to useless, it was so low in resolution and hard to see.
Cheers
Cheers

Yeah, I thought I'm safe since 80% gave no zebras, but I was wrong. It's pretty badly overexposed, and I'm not sure if I can use this material after all.

If I just had known I would have been more careful. So for the future, when in film mode, I will:
-be mindful about the white balance if not shooting raw
-be careful not to have any zebras on the subject at 75%
-trust histogram more than the zebras

Yet i'm still quite disappointed by the manual. AFAIK the naming scheme film and video don't follow any standard, and it's not apparent in any context how those relate to gamma curves and exposure. This was not a pleasant experience.
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Denny Smith

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Re: Exposing with BMPCC

PostSat Oct 06, 2018 8:24 pm

Yes, the original Pocket camera is not a point and shoot, even though it looks like one. It was designed as an alternative camera for experienced users, not really a beginner’s camera, so the manual is rather sparse.

Shooting “Video” is a backed in more fixed image, that has to have its colormbalance snd exposure set correctly from the start. But correctly recorded, it gives a ready to use video, with not additional post production corrections required. This has minimum latitude for exposure (dynamic range)

Shooting “Film” is actually a flat (color wise) film log file, which needs further corrections and adjustments in post production. Has better latitude and allows for some under/over exposure correction, in addition to color balance adjustments.

Raw, is a basic file thst needs complete processing in post production, kind of like shooting a negative film stock. This gives maximum latitude/dynamic res Ge, can be fixed for under/over exposure and set color balance to suit the situation, has most flexiblility in post production processing. Color balance and ISO are not fixed at time of shooting, as they are in film log.


A good introduction to digital cinema cameras is Barry Green’s Panasonic guide books, th elated to written for the EVA1. I have his AF100 book, a pen advanced camera aimed at new cinematographers, si goes j to some detail on zebras, setting exposure and using various exposure tools. Worth a read, regardless of the camera you are using.
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Denny Smith
SHA Productions
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v493ymb98

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Re: Exposing with BMPCC

PostSat Oct 06, 2018 9:04 pm

Denny Smith wrote:Yes, the original Pocket camera is not a point and shoot, even though it looks like one. It was designed as an alternative camera for experienced users, not really a beginner’s camera, so the manual is rather sparse.

Shooting “Video” is a backed in more fixed image, that has to have its colormbalance snd exposure set correctly from the start. But correctly recorded, it gives a ready to use video, with not additional post production corrections required. This has minimum latitude for exposure (dynamic range)

Shooting “Film” is actually a flat (color wise) film log file, which needs further corrections and adjustments in post production. Has better latitude and allows for some under/over exposure correction, in addition to color balance adjustments.

Raw, is a basic file thst needs complete processing in post production, kind of like shooting a negative film stock. This gives maximum latitude/dynamic res Ge, can be fixed for under/over exposure and set color balance to suit the situation, has most flexiblility in post production processing. Color balance and ISO are not fixed at time of shooting, as they are in film log.


A good introduction to digital cinema cameras is Barry Green’s Panasonic guide books, th elated to written for the EVA1. I have his AF100 book, a pen advanced camera aimed at new cinematographers, si goes j to some detail on zebras, setting exposure and using various exposure tools. Worth a read, regardless of the camera you are using.
Cheers

Hey Denny, thank you for putting in the effort to guide me.

This is quite familiar subject to me, but what I did not understand when going for a shoot was that I can not expose with zebras when using film mode. I would have shot raw, but 270mb/sec or so was too much.

That's why it's sad that if I would have had hints on how to do it right, I would most likely not had any problems delivering the results I was expecting. I must say the things you tell me are for the most part familiar to me already, but what was not was how to expose the image. I see no point any more using BMPCC if I'm unable to wield it's power without extensive set of monitors etc. that allow me to actually get the exposure right. Otherwise I can just shoot video with any MFT camera.

Why I chose those now was the price and the film-like image quality.

I do understand now the relation of the log curve to the percentage of exposure, and it's quite clear that that's where I screw it up. This did teach me a bunch, but I hope it's not going to teach my client as much.

This included, I don't think I can ever have as bad a shooting day as I did, but that's another story.

edit: This is what I'm seeing, right? 75% of dynamic range mapped to log curve, not 75% of light falling on sensor interpreted in exposure values?
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Denny Smith

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Re: Exposing with BMPCC

PostSat Oct 06, 2018 9:44 pm

Yes, the Pocket camera’s monitor does not really show much, as I previously mentioned, I would but the SmallHD Focus in it, Mount the included bracket to the camera top, and you can see what is going on, have False color exposure tools that work with Film Log, and get much better results.

Meanwhile do not get discouraged, soot some tests under different lighting to see what works for you, and get some practice using it. It can be a great little camera. I would also get something like the Wooden Camera half cage on it, with the hdmi cable clamp kit, there is one for sale on BMUser, should fitmthe bill for you.
Cheers
Denny Smith
SHA Productions
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v493ymb98

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Re: Exposing with BMPCC

PostSat Oct 06, 2018 10:00 pm

Denny Smith wrote:Yes, the Pocket camera’s monitor does not really show much, as I previously mentioned, I would but the SmallHD Focus in it, Mount the included bracket to the camera top, and you can see what is going on, have False color exposure tools that work with Film Log, and get much better results.

Meanwhile do not get discouraged, soot some tests under different lighting to see what works for you, and get some practice using it. It can be a great little camera. I would also get something like the Wooden Camera half cage on it, with the hdmi cable clamp kit, there is one for sale on BMUser, should fitmthe bill for you.
Cheers

Hey thanks for the tip, I'm in Europe though and renting my cameras so far, so I would need to get an actual BMPCC of my own first - which I was thinking of doing actually. If I'm going to take that path, I need to invest to those apparel as well, which I need to bake in to my cost calculations.

Btw. downloaded the Barry Green stuff and looking good so far.

I'm so much wiser now, but it won't help with the interviews that I need to deliver to my client any more, I'll just need to try some magic in the edits and post and hope it'll do for them, since I cannot afford to shoot those again.

Phew, it's a frightening ride now.
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Denny Smith

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Re: Exposing with BMPCC

PostSun Oct 07, 2018 9:41 pm

If you are thinking about buying a camera, and doing mostly interviews, you might want to consider the new Pocket Cinema Camera 4K, only $1295 with Resolve Studio 15 included.
Cheers
Denny Smith
SHA Productions

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