BMPCC 4K and the infamous ISO chart

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John Paines

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BMPCC 4K and the infamous ISO chart

PostTue Jan 08, 2019 4:14 pm

I wish the staff would clarify, once and for all, the uses of ISO settings within each circuit, in language a beginner will understand. You have people all over the 'net insisting that 1000, with or without ND, is the best setting for bright conditions because the chart, as they read it, is telling them that they'll capture actual extra stops of highlights, versus lower ISOs.

Granted, 5+ years of lousy grading from BMD cameras posted to youtube and elsewhere, some of it looking like barely boiled log, clearly didn't kill BMD sales, so the hapless ISO choices of the masses won't make any difference either. But how about some "education outreach"?

OTOH, if *I'm* the idiot and the engineers agree with the 'net, let's hear it, and long live the chart.
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Oyvind Fiksdal

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Re: BMPCC 4K and the infamous ISO chart

PostTue Jan 08, 2019 11:20 pm

Maybe it’s the dual ISO switch that happens that put people off. Going from 1000 to 1250 can seem quite harsh because it seems like you lose a lot of latitude switching from 1000 to 1250. Maybe that is why people believe 1000 is so great? I haven’t seen any big advantaged going from 400 to 1000 regard latitude. But 1000 ISO sure gives you a lot of bad noise : )

Personally, I recommend to stay at 400 for best IQ and less noise. The camera also likes to be overexposed rather than underexposing. Like a Canon oppose to a Nikon. Staying at the far-right side on your scope at iso 400 controlling with a ND will give you tons of latitude in RAW with a low noise signal. Even underexposing in 400 iso seem better than switch to 1250 in some cases, regard latitude.
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dsorbera

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Re: BMPCC 4K and the infamous ISO chart

PostWed Jan 09, 2019 12:13 am

Just looking at the chart before I got my camera I thought the same thing. But in practice I avoid iso 1000 like the plague. It's just so noisy! It looks comparable to iso 6400, which is usable, but not ideal.

I generally try to shoot iso 400 for bright stuff (but I will go to 100 when it's a very bright sunny day) and iso 1250 for anything iso 400 is too dark for. I only have to go to 3200 every once in a while (using fast lenses and a speedbooster) and I never go above 6400 no matter what. Could I get away with more? Sure. But I prefer as clean of an image as I can get, and honestly if you need to go higher than 6400 with an f1.1 lens, your doing something wrong.

Just expose your shots correctly and don't worry about how much latitude you have above or below your middle grey...
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John Paines

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Re: BMPCC 4K and the infamous ISO chart

PostWed Jan 09, 2019 12:29 am

dsorbera wrote:Just expose your shots correctly and don't worry about how much latitude you have above or below your middle grey...


That approach can and will lead to ISO choices, in lieu of actual exposure changes -- not a good idea, in my view. Which leads us back to the original question. That chart is causing all kinds of confusion, among typical buyers of the camera. Is it really going to be the last word from BMD?
Last edited by John Paines on Wed Jan 09, 2019 1:50 pm, edited 2 times in total.
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joe12south

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Re: BMPCC 4K and the infamous ISO chart

PostWed Jan 09, 2019 12:37 am

Image
I compiled this from a combination of BMD's published information and my own testing.

Note: There is nothing special about the "native" ISO, or any other one, within the same range. (This was confirmed by BMD's Captain Hook on bmcuser.com.) "Native" merely refers to BMD's recommendation for the best balance of settings.
Pocketluts: Purpose-built LUT system for the Black Magic Design Pocket Cinema Camera 4K
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John Paines

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Re: BMPCC 4K and the infamous ISO chart

PostWed Jan 09, 2019 12:40 am

Yes, you've reproduced the chart. But that's not the issue.
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joe12south

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Re: BMPCC 4K and the infamous ISO chart

PostWed Jan 09, 2019 12:53 am

We're all making this a lot more complicated than it really is. There's LOW ISO and HIgh ISO. (And a bunch of EXTENDED ISOs that you should expect to always be noisy and can't adjust.)

ISO 1000 is just ISO 100 with post-gain applied.
ISO 6400 is just ISO 1250 with post-gain applied.
Each step above ISO 6400 has analog gain applied.

Everything that happens with your image will make sense if think about it through the above filter.
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joe12south

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Re: BMPCC 4K and the infamous ISO chart

PostWed Jan 09, 2019 12:56 am

John Paines wrote:Yes, you've reproduced the chart. But that's not the issue.

No, there's a lot more useful information there. For example, BMD had never explicitly published a chart making it clear that each step above ISO 6400 bakes progressively more analog gain into the image.

Additionally, BMD had not previously explained that "native" doesn't have any real technical meaning.
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John Paines

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Re: BMPCC 4K and the infamous ISO chart

PostWed Jan 09, 2019 12:59 am

I realize you're trying to be helpful, but as detailed above, there's a wealth of seeming misinformation circulated by owners of the camera, based on what I think is a misreading of the chart, which the chart itself invites. Your own version of the chart could be seen to perpetuate that confusion -- your notation opposite 1000.

So given that confusion, my question is, why doesn't BMD clarify the issue once and for all? That doesn't mean you or me clarifying it.
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Sean van Berlo

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Re: BMPCC 4K and the infamous ISO chart

PostWed Jan 09, 2019 2:25 pm

What do you want them to clarify? If ISO 1000 is too noisy for your taste? Because that's entirely up to you. They've supplied the technical information, you get to determine what you do with that.
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John Paines

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Re: BMPCC 4K and the infamous ISO chart

PostWed Jan 09, 2019 2:51 pm

The "technical information" provided is confusing most buyers of the cameras, as any review of other forums will attest. "Captainhook" also wrote elsewhere that the information is inaccurate.

Everyone is not as confident and well-informed as you are, so I'm not sure what you gain by objecting to a clarification of the matter. Folks are still arguing over the function of ISO in the BMPCC and other early cameras, with rife false claims, so it's nothing new. It could also turn out *you're* misinformed. Imagine that....
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Sean van Berlo

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Re: BMPCC 4K and the infamous ISO chart

PostWed Jan 09, 2019 3:15 pm

Where did you see Captain Hook saying that information was inaccurate? And my question wasn't facetious, I genuinely don't understand what you want them to clarify. They've shown how changing the iso shifts the exposure curve. Other people in this thread have as well. If you're confused about what this means for your shooting, here's a guy explaining it for the Arri: https://www.provideocoalition.com/alexa ... d_to_know/
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John Paines

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Re: BMPCC 4K and the infamous ISO chart

PostWed Jan 09, 2019 3:19 pm

I see ... Art Adams explained it ten years ago, after testing a completely different camera. That answers everything!

I'm not convinced that you and others here actually do understand it. If that offends you, sorry. But, given the amount of conflicting information floating around, it might be helpful to hear from the company.
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John Paines

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Re: BMPCC 4K and the infamous ISO chart

PostWed Jan 09, 2019 4:13 pm

Sean van Berlo wrote:Where did you see Captain Hook saying that information was inaccurate?


Captain Hook, From the bmcuser.com forum:

The over/under numbers [on the chart] aren't correct. Its more like 5.5 over at ISO400/4000 for reference. To be fair, I just checked the manual and the numbers in there are not correct either so we will get those corrected.

Still convinced there's nothing to be learned?
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Sean van Berlo

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Re: BMPCC 4K and the infamous ISO chart

PostWed Jan 09, 2019 4:40 pm

There's PLENTY to learn, I love learning! At what point did I imply there was nothing to improve or learn? I'm just confused what your question is? That Hook comment is interesting, thanks for sharing! And the Art Adams article is relevant because the underlying principle is, as far as I know, is exactly the same for these cameras.

What IS your question that Blackmagic needs to answer? All their documentation just states that increasing the iso gives you more stops above middle grey and less below. This just means that on shots where there is a lot of the scene much brighter than your subject, and when you want to protect these highlights, you'd theoretically do well to increase the iso (at least until the second gain kicks). This comes at the cost of shadow detail. However, changing this curve also increases noise- the camera is not iso invariant. Whether that increased noise (and loss of shadow detail) is worth the highlight retention to you is not something Blackmagic, or anyone else for that matter, can answer. It depends on your scene and on your personal taste.
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joe12south

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Re: BMPCC 4K and the infamous ISO chart

PostWed Jan 09, 2019 4:49 pm

Not to speak for John, but I have to agree that there is so much misunderstanding and misinformation surrounding what "ISO" and dual "native" actually mean in the context of RAW that it behooves BMD to publish a single, clear description of what is actually happening in camera. A short-ish white paper would be perfect.
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John Paines

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Re: BMPCC 4K and the infamous ISO chart

PostWed Jan 09, 2019 4:53 pm

Sean van Berlo wrote:And the Art Adams article is relevant because the underlying principle is, as far as I know, is exactly the same for these cameras.


No, I don't believe the Art Adams article is necessarily relevant, since his findings are based on tests of a particular camera ("as far as you know" doesn't go very far), and he himself goes to some lengths in the article to qualify his conclusions, use this information at our own risk, I'm not responsible.

That aside, I'm familiar with your views. And I have views of my own, based on my own testing, which is at odds with received wisdom in places like the Facebook group. However, this question is being addressed to BMD staff, which provided the chart. I'm not sure why you can't accept that, without either objecting to the question or supplying your own understanding of the matter.

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