BMCC ISO optimum setting in manual.

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Fred Trevino

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BMCC ISO optimum setting in manual.

PostWed Aug 07, 2013 5:26 am

Hi everyone,

Was just reading the manual of the black magic cinema camera and I found it interesting that it said that the optimum ISO setting is 800... Does anyone else find this interesting? I've copy and pasted what the manual read below:

"ISO settings are helpful when you are shooting in a variety of light conditions. The optimum ISO setting for the Blackmagic Cinema Camera is 800ASA. Depending on your situation, however, you may choose a lower or higher ISO setting."

Anyone have a idea why they seem to be highlighting this ISO?
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Dmitry Kitsov

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Re: BMCC ISO optimum setting in manual.

PostWed Aug 07, 2013 5:31 am

This has been known to be a native iso of the sensor for quite a while.
What's more interesting is this "For Production Camera 4K choose the lowest ISO for the available lighting conditions"
Dmitry Kitsov
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Fred Trevino

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Re: BMCC ISO optimum setting in manual.

PostWed Aug 07, 2013 5:49 am

Dmitry Kitsov wrote:This has been known to be a native iso of the sensor for quite a while.
What's more interesting is this "For Production Camera 4K choose the lowest ISO for the available lighting conditions"


So by 'native' it means less noise? Better image in some way? What are the benefits of shooting in 800, say on a bright day vs 200?

Thanks!
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Tom

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Re: BMCC ISO optimum setting in manual.

PostWed Aug 07, 2013 5:57 am

FTColorist wrote:
Dmitry Kitsov wrote:This has been known to be a native iso of the sensor for quite a while.
What's more interesting is this "For Production Camera 4K choose the lowest ISO for the available lighting conditions"


So by 'native' it means less noise? Better image in some way? What are the benefits of shooting in 800, say on a bright day vs 200?

Thanks!



Some image sensors have Analogue gain applied in order to push the image sensor to different ISO settings without causing too big a shift in noise or dynamic range. Others do not have this analogue gain and so the sensor is always operating at its native ISO.
The BMCC and BMPCC have the latter. The Sensor is always at iso 800. This setting allows for the greatest dynamic range. If you set the camera to any other iso setting, it is just being push or pulled digitally.

At ISO 400 for example, you have a smoother image, but slightly lower dynamic range - this is because the image is being recorded at 800 and then pulled to 400, which pushes the noise floor lower.

At ISO 1600, the camera does apply a bias towards the shadows during the sensor readout from analogue to digital - but the sensor is still operating at 800.

If you did shoot at iso 200 on a bright sunny day for example, what you would be doing is capturing in camera at iso 800 - then pulling the exposure down digitally, which would lower the dynamic range of the shot, but also clean it up too. Because the sensor is always running at 800, the clipping in the highlights stays the same at 200 as it is at 800 - so turning down the ISO is not an efficient way to reduce the brightness of the scene -as it loses dynamic range. Much better to use an ND filter.

Some users have concluded that they prefer to shoot at ISO 400, because the image is cleaner and the DR loss is minimal.

When filming in Raw, the pulling or pushing is flagged to be done during the processing of the footage, its just meta data applied to ISO 800 footage. When filming in ProRes or DNxHD, the pushing or pulling is baked into the video file.

I hope this helps.
Last edited by Tom on Wed Aug 07, 2013 6:00 am, edited 1 time in total.
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Re: BMCC ISO optimum setting in manual.

PostWed Aug 07, 2013 5:59 am

In my case, i never ever change ISO on prores. Its the optimum dynamic range for the camera, any other ISO, your footage would suffer. Iso changes is roughly changing of gamma

Example: set zebra to 100% point to a bright source. Recognizet he pattern. Now switch to iso200, pattern hasnt changed but your image got darker.

EDIT: what tom said.
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Tom

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Re: BMCC ISO optimum setting in manual.

PostWed Aug 07, 2013 6:03 am

dustinuy wrote:In my case, i never ever change ISO on prores. Its the optimum dynamic range for the camera, any other ISO, your footage would suffer. Iso changes is roughly changing of gamma

Example: set zebra to 100% point to a bright source. Recognizet he pattern. Now switch to iso200, pattern hasnt changed but your image got darker.



If you like to ETTR when filming RAW (which is not a bad idea) - it is better to do this in camera when shooting ProRes, as it is not a raw/uncompressed format. Shooting at ISO 400 in ProRes would be like ETTR - as long as you are not clipping anything vital, you will improve the noise in the shot (should you wish to minimise noise of course ;-) )
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Re: BMCC ISO optimum setting in manual.

PostWed Aug 07, 2013 6:09 am

Tom wrote:
FTColorist wrote:
Dmitry Kitsov wrote:This has been known to be a native iso of the sensor for quite a while.
What's more interesting is this "For Production Camera 4K choose the lowest ISO for the available lighting conditions"


So by 'native' it means less noise? Better image in some way? What are the benefits of shooting in 800, say on a bright day vs 200?

Thanks!



Some image sensors have Analogue gain applied in order to push the image sensor to different ISO settings without causing too big a shift in noise or dynamic range. Others do not have this analogue gain and so the sensor is always operating at its native ISO.
The BMCC and BMPCC have the latter. The Sensor is always at iso 800. This setting allows for the greatest dynamic range. If you set the camera to any other iso setting, it is just being push or pulled digitally.

At ISO 400 for example, you have a smoother image, but slightly lower dynamic range - this is because the image is being recorded at 800 and then pulled to 400, which pushes the noise floor lower.

At ISO 1600, the camera does apply a bias towards the shadows during the sensor readout from analogue to digital - but the sensor is still operating at 800.

If you did shoot at iso 200 on a bright sunny day for example, what you would be doing is capturing in camera at iso 800 - then pulling the exposure down digitally, which would lower the dynamic range of the shot, but also clean it up too. Because the sensor is always running at 800, the clipping in the highlights stays the same at 200 as it is at 800 - so turning down the ISO is not an efficient way to reduce the brightness of the scene -as it loses dynamic range. Much better to use an ND filter.

Some users have concluded that they prefer to shoot at ISO 400, because the image is cleaner and the DR loss is minimal.

When filming in Raw, the pulling or pushing is flagged to be done during the processing of the footage, its just meta data applied to ISO 800 footage. When filming in ProRes or DNxHD, the pushing or pulling is baked into the video file.

I hope this helps.



GREAT help! Thanks Tom.
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Thomas Schumacher

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Re: BMCC ISO optimum setting in manual.

PostWed Aug 07, 2013 7:40 am

Thanks a lot for your long nice explanation above, Tom.

Now I've got a question:

Tom wrote:If you like to ETTR when filming RAW (which is not a bad idea) - it is better to do this in camera when shooting ProRes, as it is not a raw/uncompressed format. Shooting at ISO 400 in ProRes would be like ETTR - as long as you are not clipping anything vital, you will improve the noise in the shot (should you wish to minimise noise of course ;-) )


So in ProRes filmlog you don't ETTR and shoot with ISO400 to minimize noise?
But does this retain as much dynamic range (available in in ProRes) as possible (as native ISO is 800)?
I realized that when I compare some standard shots I did ETTR in ProRes filmlog with exposing them the "traditional" way (kind of wysiwyg) there is no great difference in the outcome, but I haven't done any closer examination.

(A little OT: what puzzles me is the clean image of the blacks when you're filming in darkness and someone is using a lighter to lit the scene in a close up - because if you underexpose e.g. the shadows in a standard shot get noisy and muddish. Is there any exlanation why?)

Thanks a lot!
Thomas

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Re: BMCC ISO optimum setting in manual.

PostWed Aug 07, 2013 3:59 pm

gmf wrote:Thanks a lot for your long nice explanation above, Tom.

Now I've got a question:

Tom wrote:If you like to ETTR when filming RAW (which is not a bad idea) - it is better to do this in camera when shooting ProRes, as it is not a raw/uncompressed format. Shooting at ISO 400 in ProRes would be like ETTR - as long as you are not clipping anything vital, you will improve the noise in the shot (should you wish to minimise noise of course ;-) )


So in ProRes filmlog you don't ETTR and shoot with ISO400 to minimize noise?
But does this retain as much dynamic range (available in in ProRes) as possible (as native ISO is 800)?
I realized that when I compare some standard shots I did ETTR in ProRes filmlog with exposing them the "traditional" way (kind of wysiwyg) there is no great difference in the outcome, but I haven't done any closer examination.

(A little OT: what puzzles me is the clean image of the blacks when you're filming in darkness and someone is using a lighter to lit the scene in a close up - because if you underexpose e.g. the shadows in a standard shot get noisy and muddish. Is there any exlanation why?)

Thanks a lot!
Thomas

bmc-darkness-still.jpg



ETTR at iso 800 in Raw or exposing normally in ProRes at 400 are basically the same thing. If you have the headroom without clipping, ETTR at 400 would suggest you could just dial it down to 200.

ETTR at 800 is basically filming at iso 800, but then pulling the exposure down to a lower level in post. Setting the Camera to anything below 800 in a non Raw mode, is basically taking the iso 800 sensor image and pulling it down in camera to your iso level - then saving it as a compressed format such as ProRes.

As for the noise in shadows question - the key here is the fact that the noise floor on the sensor is fixed. So you could shoot with a lens cap on and get a clean black, as long as you dont try to push the footage at all or film above 800. If you film at 400 or lower, the noise floor is pushed down even lower. The noise appears when you try to bring up the shadows with insufficient overall light. A lack of light in general does not cause noise to appear, what causes it to appear is when the noise floor is lifted higher. At 800, you will see a slight bit of noise - this is normal. At lower ISO's, I doubt you will see any at all (unless pushed).
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Re: BMCC ISO optimum setting in manual.

PostWed Aug 07, 2013 5:49 pm

Thanks a lot, Tom!
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Re: BMCC ISO optimum setting in manual.

PostWed Aug 07, 2013 8:40 pm

Thanks Tom for explaining, I didn't know this.

Blaine Russom

Re: BMCC ISO optimum setting in manual.

PostThu Aug 08, 2013 2:13 pm

Thats awesome Tom thanks!
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Re: BMCC ISO optimum setting in manual.

PostThu Sep 05, 2013 7:45 am

Dmitry Kitsov wrote:This has been known to be a native iso of the sensor for quite a while.
What's more interesting is this "For Production Camera 4K choose the lowest ISO for the available lighting conditions"


Is there any light anyone can shed on this yet? Does anyone know if the new 4K sensor will have the analogue option Tom was mentioning? I guess a better question would be, does anyone know what sensor they're putting in yet?
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Re: BMCC ISO optimum setting in manual.

PostThu Sep 05, 2013 8:33 am

Very nice explanation Tom. This should be added to the FAQ as it's the best (simple and clear to understand) explanation I've read to date.
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Re: BMCC ISO optimum setting in manual.

PostThu Sep 05, 2013 8:34 am

iml wrote:
Dmitry Kitsov wrote:This has been known to be a native iso of the sensor for quite a while.
What's more interesting is this "For Production Camera 4K choose the lowest ISO for the available lighting conditions"


Is there any light anyone can shed on this yet? Does anyone know if the new 4K sensor will have the analogue option Tom was mentioning? I guess a better question would be, does anyone know what sensor they're putting in yet?


If I'm not mistaken BM stated in an interview that the BMPC4K sensor has a lower base ISO. This is probably what they mean in the manual. They may not have finalised what the base ISO is when they wrote the manual. Expect an update when the camera ships.
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Re: BMCC ISO optimum setting in manual.

PostThu Sep 05, 2013 6:00 pm

Dmitry Kitsov wrote:... What's more interesting is this "For Production Camera 4K choose the lowest ISO for the available lighting conditions"


This is quite interesting since the section on ISO does not differentiate between raw and ProRes ISO settings. It also indicates a lower ISO setting will give richer colours. Looking forward to learning how to expose best in various conditions with the BMPC4K sensor. It may not be identical to how to achieve the desired exposure with the BMCC and BMPCC.

Rick Lang
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Re: BMCC ISO optimum setting in manual.

PostThu Sep 05, 2013 7:34 pm

So in prores you ETTR in 800, and then take it down a stop by switching it to 400? Or just ETTR in 400 and leave it there?

(don't yet really get it, sorry :cry: )
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Re: BMCC ISO optimum setting in manual.

PostThu Sep 05, 2013 8:28 pm

adamroberts wrote:
iml wrote:
Dmitry Kitsov wrote:This has been known to be a native iso of the sensor for quite a while.
What's more interesting is this "For Production Camera 4K choose the lowest ISO for the available lighting conditions"


Is there any light anyone can shed on this yet? Does anyone know if the new 4K sensor will have the analogue option Tom was mentioning? I guess a better question would be, does anyone know what sensor they're putting in yet?


If I'm not mistaken BM stated in an interview that the BMPC4K sensor has a lower base ISO. This is probably what they mean in the manual. They may not have finalised what the base ISO is when they wrote the manual. Expect an update when the camera ships.



Thanks Adam this makes sense, I was just trying to put feelers out there to see if there was new info..can't wait to start working with the Production Camera!
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Re: BMCC ISO optimum setting in manual.

PostThu Sep 05, 2013 8:52 pm

MatthijsLiethof wrote:So in prores you ETTR in 800, and then take it down a stop by switching it to 400? Or just ETTR in 400 and leave it there?

(don't yet really get it, sorry :cry: )



In ProRes mode, any ISO under 800 is exposing to the right. As long as you arent clipping anything important, you are ok.
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Re: BMCC ISO optimum setting in manual.

PostFri Sep 06, 2013 1:16 am

Tom wrote:
MatthijsLiethof wrote:So in prores you ETTR in 800, and then take it down a stop by switching it to 400? Or just ETTR in 400 and leave it there?

(don't yet really get it, sorry :cry: )



In ProRes mode, any ISO under 800 is exposing to the right. As long as you arent clipping anything important, you are ok.



Wouldn't this only be true in RAW mode ? (technically it wouldnt matter)

Since ETTR makes use of more "levels" of the 10 bit file?

as 400 or 800, most shadows and mid-tones live in only have of the file don't they, between 0-512?


My reasoning is that since the ISO values are baked into a pro res, than exposing at 400 is not only making not much difference than what an nd filter could do for you , but also at a more limited DR


Please correct me if i'm wrong, I don't care much about being right as long as I'm able to get the facts straight


Thank you
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matthijsliethof

Re: BMCC ISO optimum setting in manual.

PostFri Sep 06, 2013 8:54 am

Tom wrote:In ProRes mode, any ISO under 800 is exposing to the right. As long as you aren't clipping anything important, you are ok.


Always trust the Zebra then, because if it's clipping there you lost it?

The ProRes has enough room to pull down something overexposed(no clipping by zebra's) in post?


So you point the camera, use the ND filter @ 800 asa to choose what you want to clip or not and then do pulldown in camera with asa 400 or 200? (to bring down the noise floor?)
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Re: BMCC ISO optimum setting in manual.

PostSun Sep 08, 2013 3:36 pm

pacman829 wrote:
Tom wrote:
MatthijsLiethof wrote:So in prores you ETTR in 800, and then take it down a stop by switching it to 400? Or just ETTR in 400 and leave it there?

(don't yet really get it, sorry :cry: )



In ProRes mode, any ISO under 800 is exposing to the right. As long as you arent clipping anything important, you are ok.



Wouldn't this only be true in RAW mode ? (technically it wouldnt matter)

Since ETTR makes use of more "levels" of the 10 bit file?

as 400 or 800, most shadows and mid-tones live in only have of the file don't they, between 0-512?


My reasoning is that since the ISO values are baked into a pro res, than exposing at 400 is not only making not much difference than what an nd filter could do for you , but also at a more limited DR


Please correct me if i'm wrong, I don't care much about being right as long as I'm able to get the facts straight


Thank you



The point with ProRes and lowering the ISO is not to reduce the overall clipping point within a scene - as the sensor clipping is the same regardless as to whether you are at 800, 400, 200 etc. The point is that the iso 800 image is being pulled down digitally within the camera and then being compressed into a prores file.

If you were shooting in Raw, the digital pulling down of the exposure would happen in resolve when you play back the dng files. Because the ProRes files will have limited flexibility due to them being compressed, it is better to have the digital pull down occur before the compression occurs, rather than after. In Raw there is no compression and its just meta data in camera.
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Re: BMCC ISO optimum setting in manual.

PostTue Dec 17, 2013 3:56 pm

I've been shooting at iso 400 with prores after reading this thread. I did try 800 once but got strange lines in the shadows [banding I think] so I've not tried that again. The noise is minimal [and unlike DSLR noise it looks very pleasing to the eye]. I've shot in a lot of low light locations and during a thunderstorm for my ghost film and had no trouble.
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Re: BMCC ISO optimum setting in manual.

PostTue Feb 04, 2014 12:19 pm

Hi.

For preparing for a short, we've shooted a k-light comparative the ikonoskop and the bmpc in both dng.

The bmpc dng images imported in davinci were shooted at 200 and 400 iso.

The range @ 400 apeared to be clearly higher then @ 200. Specially in hightlights.

Why the setting would have influance on the raw file?

Does it mean that the 200 KL image is a kind of balanced 800iso image down-exposed to 200? Should be the same result as a 200 KL+ 2 stop down-graded to have a density of a KL-exposed image?
Last edited by Ryszardkarcz on Tue Feb 04, 2014 12:55 pm, edited 1 time in total.
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Re: BMCC ISO optimum setting in manual.

PostTue Feb 04, 2014 12:34 pm

Ryszardkarcz wrote:Hi.

For preparing for a short, we've shooted a k-light comparative the ikonoskop and the bmpc in both dng.

The bmpc dng images imported in davinci were shooted at 200 and 400 iso.

The range @ 400 apeared to be clearly higher then @ 200. Specially in hightlights.

Why the setting would have influance on the raw file?


Regardless of whether you set it to 200,400 or 800 - the raw dng files are exactly as they would be if just shot at 800. When you open in them up in resolve, it looks at the metadata tags associated with the dng sequence. One of the tags lets resolve know what iso it was filmed at in camera, and this value is classed as "0" in the exposure section of the raw tab.

For example, If you set it to 200 in camera and then in resolve set it to +1 exposure, it would be exactly the same as if shot at 400. If you set it to 800 in camera and then in resolve set it to -2 exposure, it would be exactly the same as if you shot it at 200 in camera.

So because you have set it at 400 and 200 - it will look brighter - but there is no additional data, it is just applying a different exposure curve in resolve on playback.
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Re: BMCC ISO optimum setting in manual.

PostTue Feb 04, 2014 1:01 pm

ok, right, that make sense.

Haven't found untill now any clear tests about bmpc real iso. 800 is the best way to expose it occure now.
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Re: BMCC ISO optimum setting in manual.

PostTue Feb 04, 2014 1:14 pm

Ryszardkarcz wrote:ok, right, that make sense.

Haven't found untill now any clear tests about bmpc real iso. 800 is the best way to expose it occure now.



Indeed, the native iso is 800 - expose your scene for 800 and you will capture the widest dynamic range. If you are ok with loosing a stop or two and want a cleaner image, use a lower value such as 400 or 200.
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Re: BMCC ISO optimum setting in manual.

PostTue Feb 04, 2014 1:53 pm

Using 200 appears to be rather dangerous, if used outside you will loose a lot of information in all highlights, has the dinamic will be completely knoked off by 2 stops on the hight part of the curve.

In any kind of conditions, the lower iso will be over-exposed for two stop and compensated, means noise, color aberations etc.

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