BMPCC - What is it's true ISO?

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Daniel Meier

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BMPCC - What is it's true ISO?

PostMon Jan 29, 2018 7:36 pm

I've been owning a BMPCC for about half a year now. And been shooting with someone else's one for years.

It's still hard for me to understand the ISO Setting when shooting Prores in Film Log.
It's surely not your regular ISO switching process like on other Log cameras (e.g. FS 700 or C300).
If you only dial the ISO down from 800 to 200 (shutter and iris remain unchanged) the difference in exposure is not globally. The image seems to become more contrasty in the shadows. But you don't gain any highlight detail. Once blown out in ISO 800 setting it will also be blown out at ISO 200.

Anyways. My real point about this topic is this:
Lately I've been shooting with the Pocket using my light meter (Sekonic L308DC).
I always kept the ISO at 800. So I did some reading with the ligh meter and always ended up with an underexposure on the Pocket. After some messing around, I found out that the Pocket's real ISO sensitivtiy is ASA 100.

This applies when shooting in Prores and Film Mode.
However whenever I switched to Video Mode, my meter was right. Asa 800 in the meter was corresponding to ISO 800 in the camera.

Any thought's on that?
I find it really disillusioning to shoot with a camera that good but being limited to a native ISO of 100.
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Denny Smith

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Re: BMPCC - What is it's true ISO?

PostTue Jan 30, 2018 1:41 am

No, the native ISO on the Pocket camera is 800. Shooting in Film Log, gives what looks like a flat underexposed image, but one processed in Resolve, gives a normal looking image and good color saturation yiu can grade as you like. Think of Film Log as something between a Raw and Rec 709 Video mode.

As clipping goes, once the sensor clips, data is lost, regardless of the mode,yiu are shooting in. Film log gives a little wider dynamic range than Video mode does, Raw add more dynamic range by a stop or so. Changing ISO doesn’t really change the exposure, just the contrast curve, it moves mid grey point up or down in relation highlight and shadow detail. Moving towards 200 or 100 may give more shadow detail, but drops highlights details, moving up to 800 or 1600 may give more highlight detail, but drops black detail.

To prevent clipping set your Zebras to 90%, and use them to get the exposure to where the desired highlights are not clipping. Also using a monitor or EVF with false color will help prevent clipping. But, you must still control your lighting to keep the desired subject values between clipping and crushed blacks. You need to avoid clipping your highlights (100ire), while keeping enough light in the dark areas of the scene from getting too underexposed (about 20ire).

Use your meter to measure the highest/brightest scene values and the dark area values to stay within the 10/12 stop range. Do a little experimenting to see where the sensor hits its sweet spot with the readings you get on the meter, to tune them together.
Cheers
Last edited by Denny Smith on Thu Feb 01, 2018 12:50 am, edited 1 time in total.
Denny Smith
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Anatoly Mashanov

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Re: BMPCC - What is it's true ISO?

PostTue Jan 30, 2018 2:17 am

I am a physicist, not a cinematographer, so I heretically think there is NO such thing as true ISO for BMPCC - just because the ISO is defined by blackening the classic film while in digital world you could produce any "blackening" you like and that sensibility is limited by noise. So:

1) You could (and should) think that BMPCC ISO is 800.
2) While you have enough light you should set the maximum exposition in condition that there is no clipping (ETTR) in order to minimize noise. Use zebras.
3) While you have not enough light you should fight the temptation to ETTR sacrificing the depth of field. You could produce quite nice footage by applying a noise suppressor plugin but no postprocessing could make your footage sharp.
4) I think the light meter is of little help since it measures the integral light only and does not prevent clipping. Use zebras.
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Uli Plank

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Re: BMPCC - What is it's true ISO?

PostTue Jan 30, 2018 10:26 am

No electronic camera has a true native sensitivity. You have a dynamic range, where the upper limit is a hard wall (clipping) and the lower limit is a soft swamp (noise). The upper limit is clearly defined by complete loss of image detail. The lower limit is partially subjective, depending on how much noise you want to tolerate and it can be improved to some degree by a good, temporal noise filter. In the end, you have a dynamic range.

You can decide to put your 'native' ISO just in the middle of that range, but it's an aesthetic decision rather than a scientific definition.

Just my two cents on exposure.
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John Paines

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Re: BMPCC - What is it's true ISO?

PostTue Jan 30, 2018 3:43 pm

Denny Smith wrote:Raw add more dynamic range by a stop or so.


That claim is often heard, but I have yet to see any convincing real-world proof of it. Can you direct me to any?

Denny Smith wrote: Moving towards 200 or 100 gives more shadow detail, but drops highlights details, moving up to 800 or 1600 gives more highlight detail, but drops black detail.


I've never seen any evidence that 200 (in log) offers more shadow detail with BMPCC footage, than 800. Again, is this theory or actual observation?
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Denny Smith

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Re: BMPCC - What is it's true ISO?

PostTue Jan 30, 2018 7:07 pm

Both are my observations, and the observations of others, based on using both the Pocket camera and Micro Cinema Camera. This has also been observed by others and was well discussed when the Pocket first came out. See some of John Brawley’s comments in his tests with the Pocket camera.

As for the real amount of dynamic range gain with Raw vs Film Log, it is close and perhaps somewhat subjective, but both are greater than Video Rec 709, which is a “baked” value when recorded. In Raw, ISO is just meta-data, used by Resolve as a starting point when the Raw is processed.

Yes, “Native” ISO is a subjective term in what looks good to the user, but is useually based on the ISO that delivers the best overall average image, with the least amount of sensor video noise, giving clean whites and good blacks, whithout being crushed.

On BM Cinema camera’s ISO only effects the mid gray value and the number of stops below to black, and above to white, so pick the ISO value for the situation you are shooting that looks good to you.
Last edited by Denny Smith on Sun Feb 04, 2018 6:34 am, edited 1 time in total.
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John Paines

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Re: BMPCC - What is it's true ISO?

PostTue Jan 30, 2018 7:15 pm

I understood how ISOs work, in log. That's not at issue.

With all due respect, you hear these claims (those raised in my first response) constantly repeated. Ask for evidence, and it's another matter.
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Jim Giberti

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Re: BMPCC - What is it's true ISO?

PostTue Jan 30, 2018 8:18 pm

That claim is often heard, but I have yet to see any convincing real-world proof of it. Can you direct me to any?


I can't give you specific stops nor do I have the time to dig through drives to find and post the footage but I can tell you this without reservation - yes, raw does capture more dynamic range than prores.

I've done very simple but demonstrative tests in bright outdoor lighting as it affects skin tone/exposure.

It's very simple. Try and prove it to yourself or post your contrarty results but I doubt you won't find the obvious. I've tested, on more than one occasion, fair skin in the exact same scenario with the same camera, lens, aperture and ISO and the raw image handles the highlights better with a more natural roll-off.

With that said, we shoot pretty much exclusively in ProRes. We have a pretty hectic production schedule and like most similar producers, don't have time for a raw workflow nor does the slight but comparatively noticeable difference matter for our work - TV and web spots and corporate films.

But yes, there is a difference in DR between the two formats,
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Howard Roll

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Re: BMPCC - What is it's true ISO?

PostTue Jan 30, 2018 11:27 pm

The closest you can get to shooting raw in ProRes is shooting at 1600ISO. For every stop of in camera ISO you are going to shift down mid grey and compress shadows (not lift them). You lose about a stop at the low end for every stop of shift in ISO. If you have 13 stops @ 1600ISO you'll have about 10 stops @ 200ISO. This is the tradeoff for getting cleaner imagery, if there were no loss in DR everyone would be shooting outdoors at 200ISO. Additionally the lower ISOs use less of the available range so that at 1600 ISO you'll clip at about 104IRE, 800 will clip @ 100IRE, 400 will clip @ 90IRE, and 200 will clip at 80IRE. You could argue (I wouldn't) that you don't lose dynamic range in the shadows but if you have 3 stops of dynamic range crammed into about 5 IRE worth of data it's going to be a lot harder to dig them out of 10 bit ProRes than 12 bit raw distributed across 10IRE. Additionally raw provides some highlight recovery to reconstruct detail that's not available once it's baked into ProRes.

Despite this, I don't feel raw is necessary for the majority of shooting situations assuming a shooter that isn't totally clueless.
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John Paines

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Re: BMPCC - What is it's true ISO?

PostTue Jan 30, 2018 11:53 pm

I had never heard anyone claim, before this thread, that 200 ISO (log) was better for shadow detail -- observations of the waveform suggest the opposite -- but let that one go, maybe there's some confusion somewhere

For the rest, the BMPCC has been on the market going on what, 5 years(?), and I've yet to see anyone demonstrate a 1+ stop advantage for raw over 800 ISO log, despite countless assertions to that effect. Maybe that test exists, maybe I missed it, maybe it's so obvious no one bothered to go through the motions and document it.

But, judging from the responses here, sincere as they may be, it doesn't look like anyone is going to disrupt that perfect record of assertion without proof.
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Nate Porter

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Re: BMPCC - What is it's true ISO?

PostSun Feb 04, 2018 5:04 am

FWIW I'd also like to see proof that RAW provides any meaningful improvement to DR
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Jim Giberti

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Re: BMPCC - What is it's true ISO?

PostSun Feb 04, 2018 7:33 pm

"FWIW I'd also like to see proof that RAW provides any meaningful improvement to DR"

Do you have a BM camera?
If so you can resolve the question in a few minutes yourself- no need to ask others for proof.

If you don't have a BM camera, why does it matter to you?

Not to be contentious but I just don't get the ongoing "show me proof" thing. Turn your camrera on and do a meaningful comparison.

As I said, I have, and the improved highlight roll-off is obvious.
And as I said, we shoot ProRes so I have no personal interest in hyping the comparative value of raw.
But it does improve highlight roll-off so yeah, it shows improved DR.

Try it and see.
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Jim Giberti

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Re: BMPCC - What is it's true ISO?

PostSun Feb 04, 2018 7:36 pm

[quote=" judging from the responses here, sincere as they may be, it doesn't look like anyone is going to disrupt that perfect record of assertion without proof.[/quote]


And you're continuing your perfect record of making assertions that you could prove or disprove yourself and post the evidence you keep asking for yourself.

Are you lazy, don't have a BM camera or just like to ask other people to prove things for you as if they're on call?
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John Paines

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Re: BMPCC - What is it's true ISO?

PostSun Feb 04, 2018 7:54 pm

Jim Giberti wrote:And you're continuing your perfect record of making assertions that you could prove or disprove yourself and post the evidence you keep asking for yourself.

Are you lazy, don't have a BM camera or just like to ask other people to prove things for you as if they're on call?


1) Yes, I'm lazy as hell.

2) No, I've owned a BMPCC since 2013(?)

3) despite my grave faults of character, I have performed tests, looking for that elusive 1+ stop of usable DR in raw versus Prores HQ, albeit without rigorous setups. Who, after all, doesn't want an extra stop+ of usable DR?

And, never having succeeded in finding that elusive quantum, and constantly seeing other folks claim it exists, I supposed, jerk that I am, that they must have done their own tests and that they'd be happy to produce them. After all, they went to the trouble of offering advice to others and making the assertion, repeatedly, often at great length.

But, as a reading of this thread will demonstrate, you see where these discussions invariably go.
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Howard Roll

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Re: BMPCC - What is it's true ISO?

PostSun Feb 04, 2018 9:08 pm

Well I was hesitant to post these because they require a logical "leap of faith" and do not provide a smoking gun. In both tests they show that ISO1600 in ProRes shows more dynamic range than 800ISO in ProRes. Here's the logical "leap of faith"-Unless you're arguing that ISO1600 in ProRes has more DR than raw, it stands to reason that raw has more DR than ISO800 in ProRes.

http://robsonimaging.tumblr.com/post/67 ... ith-charts
http://www.bmcuser.com/showthread.php?7 ... and-Charts
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John Paines

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Re: BMPCC - What is it's true ISO?

PostSun Feb 04, 2018 10:32 pm

Well, that's interesting, and thanks for posting it. Experience doesn't make me receptive to the logic: when I tested 1600 (log) v 800 (log) a few years ago, the results weren't encouraging. Any gain in shadow detail with 1600 was more than offset by noise, and I seemed to see earlier highlight clipping. These were real-life tests, though also imperfect for that reason.

I am aware of that discussion a few week ago about 1600 on the UMPro. Don't know how much of that applies to the BMPCC, but from what I saw, there's no enduring advantage to using 1600 on the BMPCC.
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Howard Roll

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Re: BMPCC - What is it's true ISO?

PostMon Feb 05, 2018 5:28 am

It's a little disingenuous to ask for objective results then qualify them with subjective opinions. Subjectively I agree with you, in fact I rated the Pocket sensor closer to 400 (while shooting 800) to bury the noise floor. I think Jim agrees as well that the tradeoff for raw isn't necessarily worth, it but there is a difference. Please post your tests or any tests you feel relevant that prove your point. I find it ironic that you ask for tests that prove that raw has more latitude, yet to refute my claims you provide only anecdotal evidence.
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Bill Young

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Re: BMPCC - What is it's true ISO?

PostMon Feb 05, 2018 10:26 am

Here is a simple test: Set up a controlled light scene designed for iso800, then with out adjusting the lighting or any of the lens and filter settings shoot in every ISO of RAW and every ISO of Prores. Now because the lens and filter settings were not changed the test is to make all the clips look identical. With prores your odds of complete success are next to none, but with raw, every clip can easily be made to look exactly like every other ISO, because all the sensor data is there. A simple toggle of the clips ISO will match it to any other ISO. This means raw is ISO irrelevant on these cameras where prores is not. If that doesn't demonstrate that raw has more dynamic range, then I'm not sure what will.

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