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SIGMA FP with ProRes RAW and BRAW !


Trankilstef
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In the interest of clarification I'd like to see if a few observations are correct. I am talking about DNG forward. It has been my understanding that "base ISO" is determined  by the least noise vs the highest dynamic range. Sigma has proscribed that the base ISO is 100.  I think we have established that the FP uses a linear curve. There are +/_ 12.5 stops of range.  If shot at base ISO then neutral grey should be at the middle of this. The camera's waveform and zebras are correct with this. In my understanding, changing the ISO on camera or in post results in changing the amount of information available  above or below that grey exposing properly-AKA grey is grey. If we choose, or "pretend" that the ISO is 800, we say "I choose grey will be here", whites will still clip at the same amount of light with this much light reaching the lens. We will have less information to convert the above grey-to-blown-out to the +/_ 6 stops of rec 709, but more in the below-grey-to black, which will still go black with the same lack of light amount reaching the sensor.  When changing ISO on camera The FP changes the waveform and clipping point zebras when you change the ISO! As if it is looking at an initial transform at 100, and then you are boosting that image thus indicating clipping where there is none. This makes on the fly protection of highlights and checking of black levels problematic! 

I thought maybe, use 100 ISO to check clipping, set exposure, then switch to what ISO you might choose to monitor and eventually use as the working ISO to expose grey properly. When shooting, then remember, (or make a sticker for the camera!) how many stops above or below your chosen ISO there is to that blown point or black. A spot meter is a pretty good tool to have at this point. Not great for moving fast. Or start to develop your eye. faster, but more accurate than you might think! 

This business of 3200 is a real conundrum though. If I read Rawshooter's generous contributions right, the very metering is wrong, and math with a base ISO check or a spot-meter is the only way through. And all monitoring in camera is going to be off by two stops at proper exposure. Damn. So to move quickly, dial in 3200 + look at recommended exposure, then open up two stops, deal with a blown out monitor image use it as a framing reference. Spot meter the highlights (or gage with your eye haha) to know where the image will blow out.

There is a fundamental question that is kind of pivotal to this and my understanding as a question though.  If I have a camera that has a base ISO of 100, and it has a 5 stop dynamic range (for ease of math), If I choose (shooting raw) to set the ISO at 1600 (one stop of information before blow out), when choosing a rec 709 transform, will the remaining stop of information above middle grey be parsed into the  3 stops rec 709 sees as above grey to white? Here is where I am sure I sound stupid because a stop is a stop, double the light. 

Here's a bit for thought... or telling me to shut up and that's your last glass of wine Mr. I have gotten used to looking at a good monitor and knowing what I see is what will be delivered. It is a pretty seductive thing. I shot film though for 20+ years and I see a lot of parallel with shooting RAW. When shooting film you used a meter and knew the filmstock, what it could handle, how and when it would blow out, how it would handle underexposure (black pixels matter yo! haha) You did not see the printed image for a couple of days (quicker if you were shooting for the studio!)I used a meter and knew the sensitometry of any given film stock, knew what it would matriculate to when graded. Raw seems like this. We look at a proxy image awaiting development. That sounds like knowing the sensor. I got to work with some greats, they could tell an exposure without a meter by eye. We used to play a game when I was a camera assistant on big pictures, and try to guess the shooting stop.  After a while, we nearly always got it. Practical experience of the sensor, no matter whether it's film or digital is key. Knowing the tools is the mark of a cinematographer. I'd like us to have a clear idea of how this camera deals with light, put it in in the back of our minds and then go shoot wicked cool stuff with it. 

 

 

Chart.png

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@Lensmonkey:

Raw is really the same as shooting film. Something that you should take into consideration is that middle gray practically never falls in the middle of the exposure range on negative film. You have tons of overexposure latitude, and very little underexposure latitude, so overexposing a negative for a denser image is very common. With raw on lower end cameras it is quite the opposite: you don't really have much (if any) latitude for overexposure, because of the hard clip at sensor saturation levels, but you can often rate faster (higher ISO) and underexpose a bit. This is the case, provided that ISO is merely a metadata label, which is true for most cinema cameras, and looking at the chart it is likely true for the Sigma up to around 1600, where some analog gain change kicks in.

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  • 7 months later...
  • 4 months later...

Hi all,

I have invested much time to investigate on the monitoring and ISO behavior of the fp. Finally in combination with the Ninja V I have found a working solution for me which gets both the monitoring picture and the metering right.

Basically after reading through your posts I understood that the fp is ISO invariant and has only two native ISO values available for metering and recording. (ISO 100 & ISO 3200) Others are digitally amplified. 

False color screen with the Ninja V is working on both of these ISO values to meter the correct exposure. However as a lot of you have mentioned the Rec709 monitor view is only showing the correct picture in ISO 100. The 3200 setting will be overexposed and useless.

After several tests I have figured out that if you set the Ninja V to PQ the ISO 3200 screen will look correct. Different story for ISO 100, but this can be tricked if you select ISO 400 in camera. Screen will look exactly the same now for both ISO values. Metering for ISO 100 is unaffected, since the false color mode is only showing the values for ISO 100.

Since the recorded ISO values of the Ninja V are pushed into Final Cut Pro X you will get an overblown picture in Rec709, BUT and this is really nice, if you select ISO 100 instead of ISO 400 and ISO 640 instead of ISO 3200 everything will look as expected. Correctly metered and captured. Remember, in the additional manual of the fp in regards to the ISO behavior, Sigma is mentioning ISO 100 and ISO 640 for photos...

If you need to work with Zebras the correct settings are for ISO 400 => 55% and for ISO 3200 => 60% if you want to avoid anything in the 100% range. You could go slightly higher as the fp has some more headroom over 100 IRE.

Quite a lot of hassle if you ask me, but once you have got used to this you will get a nice picture on both. 

 

Hoping this will help some of you 🙂

 

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On 7/28/2021 at 6:55 AM, OleB said:

Hi all,

I have invested much time to investigate on the monitoring and ISO behavior of the fp. Finally in combination with the Ninja V I have found a working solution for me which gets both the monitoring picture and the metering right.

Basically after reading through your posts I understood that the fp is ISO invariant and has only two native ISO values available for metering and recording. (ISO 100 & ISO 3200) Others are digitally amplified. 

False color screen with the Ninja V is working on both of these ISO values to meter the correct exposure. However as a lot of you have mentioned the Rec709 monitor view is only showing the correct picture in ISO 100. The 3200 setting will be overexposed and useless.

After several tests I have figured out that if you set the Ninja V to PQ the ISO 3200 screen will look correct. Different story for ISO 100, but this can be tricked if you select ISO 400 in camera. Screen will look exactly the same now for both ISO values. Metering for ISO 100 is unaffected, since the false color mode is only showing the values for ISO 100.

Since the recorded ISO values of the Ninja V are pushed into Final Cut Pro X you will get an overblown picture in Rec709, BUT and this is really nice, if you select ISO 100 instead of ISO 400 and ISO 640 instead of ISO 3200 everything will look as expected. Correctly metered and captured. Remember, in the additional manual of the fp in regards to the ISO behavior, Sigma is mentioning ISO 100 and ISO 640 for photos...

If you need to work with Zebras the correct settings are for ISO 400 => 55% and for ISO 3200 => 60% if you want to avoid anything in the 100% range. You could go slightly higher as the fp has some more headroom over 100 IRE.

Quite a lot of hassle if you ask me, but once you have got used to this you will get a nice picture on both. 

 

Hoping this will help some of you 🙂

 

Do you find the dynamic range lacking at all? Some talk of that early on but I feel like it may just be that more info is placed in the shadows rather than the highlights like the S1 favors. 

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1 hour ago, TomTheDP said:

Do you find the dynamic range lacking at all? Some talk of that early on but I feel like it may just be that more info is placed in the shadows rather than the highlights like the S1 favors. 

Actually you can choose the distribution of the split between highlights and shadows on your own with the Sigma fp. 

How much is above or below middle grey is a matter of the selected ISO value. Chart attached. But there is also a pdf floating in the internet which is called Sigma fp Dual Base ISO Technology. Which explains the behaviour better.

Basically the answer is, if you need as much shadow details as possible select ISO 100, if you need maximum of highlight details go for ISO 800.

Keep in mind the camera is recording ISO 100 even if you select ISO 800. So make sure you are exposing for ISO 100 if you do not want to sacrifice the quality by underexposing. And you have to dial back exposure in the editing software.

 

image.png

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  • 6 months later...

Hi all,

have done further investigation on this.

Seems (at least with the latest firmware 3.01) that in Cine mode and external ProRes Recording via Atomos Ninja V the ISO settings in camera are operating a lot different than what you think.

Monitoring mode is PQ (Rec709 is not working at all despite for ISO 100 setting in camera)

ISO 800 = ISO 100

ISO 1000 = ISO 125

ISO 1250 = ISO 160

ISO 1600 = ISO 200

ISO 2000 = ISO 320

ISO 2500 = ISO 500

ISO 3200 = ISO 640 (camera switches to second native ISO)

ISO 4000 = ISO 640 (that value is weird, does not change the picture at all)

ISO 6400 = ISO 800

ISO 8000 = ISO 1000

ISO 10000 = ISO 1250

ISO 12800 = ISO 1600

ISO 16000 = ISO 2000

ISO 20000 = ISO 2500

ISO 25600 = ISO 3200

With all these changes the false color screen / zebras are showing correct clipping values.

So if you are not clipping highlights you are always getting max dynamic range. However in the PQ mode no changes in the mid grey point are visible like in the sigma diagram posted above. That means you are not getting different distribution of stops between highlight and shadow areas. Seems that is only applicable for Rec709, but then again metering is not working with tools like false color etc, unless you stay in ISO 100.

On import to FCX just make sure, that you select the "correct" ISO value, as the camera will push through the Atomos its measures, which are not correct. Both in real world and compared to an incident meter.

 

 

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Second observation if Ninja V is set to Rec709 monitoring and you ignore the false colors. The camera ISOs and the dynamic range chart from above are indeed correct.

However that leaves you with possibly less image quality because you are underexposing in relation to sensor capabilities. Meaning more noise (which could be also a good thing if considered as filmic texture). 

Basically I think it is now for the user to decide. Most precise measurement and best image quality, go the PQ route with above mentioned ISO settings/conversation and little room for mistakes (sensor clipping quite near). For a more cinematographic measuring approach and more room for error compensation, go the Rec709 route.

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  • 1 month later...
On 7/29/2021 at 4:44 PM, OleB said:

Keep in mind the camera is recording ISO 100 even if you select ISO 800. So make sure you are exposing for ISO 100 if you do not want to sacrifice the quality by underexposing. And you have to dial back exposure in the editing software.

 

That behavior reminds me of the Nikon D7100, D7200 cameras, they were pretty much ISO less. You were just changing gain not ISO in reality. So you could just shoot at ISO 100 all the time and change it in post.

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2 hours ago, webrunner5 said:

So you could just shoot at ISO 100 all the time and change it in post

I tried that.

Once.

I couldn't get past the fact I had gotten used to mirrorless WYSIWYG and the experiment ended at that point.

But re. the whole manual vs auto iso thing, my wedding this weekend (I am still at, Day 3/3) I decided to give auto iso a go for video as well as photo.

For stills, I always shoot auto iso with a chosen aperture and min shutter speed. Except low light static shots such as buildings etc where I usually select 800 iso and trust the excellent IBIS for slower shutter speed stuff...which reminds me I could also lower my shutter speed from  min 1/250th to 1/60th or even slower...note to self for next wedding...a bit rusty after just 6 in 2.5 years!

For video though, I have always set manual ISO but as a one man band, I've experienced a few issues such as that carefully set, unmanned static ceremony cameras, exposure fixed in the sun...and then it turned cloudy on and off and...argh...

So I flipped to setting the exposure in bright sun and then set the only variable as iso and the camera can take care of that.

Used it for everything all the time and quite like that approach allowing the camera to take care of that one thing for me when the light changes. One less thing to think about.

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On 4/17/2022 at 5:18 AM, Lensmonkey said:

Does this monitoring/level mismatch occur in the screen/evf or only when externally monitored? Thank you for your informative posts regarding this phenomenon, and the sharing of knowledge!

Happens for all...EVF, LCD and external monitoring. Indeed it is a pain and would need a firmware update to be fixed...

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I greatly appreciate this camera's size, and commitment to cDNG, but I don't like the way the highlights look when they clip. The transition from not-clipped to clipped looks harsh to me. In a word, I find the highlight rolloff ugly. 

I hope I am missing something because I really want to love this camera.

Is there a way to soften this transition? Thinking out loud, maybe a bit of fake film grain would do the trick. Alternatively, is it practical to shoot with the camera in diverse environments and never let the highlights clip, underexposing at times and then raising midtones and shadows in post when necessary? Is the noise floor low enough for this to look OK? Is there much in the way of unsightly fixed-pattern noise or is it beautifully random? 

Is there a way to make the highlights beautiful all the time? Maybe shooting ISO 800 would help as it would allocate more of the DR to the highlights while maintaining the maximum DR. (Thank you OleB for the chart)

Also, does "highlight recovery" in Resolve just not work with this camera? It often renders the highlights pink no matter what colorspace and gamma I use. In the waveform it looks like there still might be data there, however.

What are the best practices when it comes to grading the cDNGs from this camera in Resolve Studio? Timur Civan had a blog about using P3 D60 colorspace in Camera Raw, rather than Blackmagic Design. He then used a colorspace transform as a node in the color tab, I think. It went a bit over my head. What are people here using for colorspace settings in Resolve Camera Raw; P3 D60, or Blackmagic Design?

Thanks for your insights.

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1 hour ago, Owlgreen said:

I greatly appreciate this camera's size, and commitment to cDNG, but I don't like the way the highlights look when they clip. The transition from not-clipped to clipped looks harsh to me. In a word, I find the highlight rolloff ugly. 

I hope I am missing something because I really want to love this camera.

Is there a way to soften this transition? Thinking out loud, maybe a bit of fake film grain would do the trick. Alternatively, is it practical to shoot with the camera in diverse environments and never let the highlights clip, underexposing at times and then raising midtones and shadows in post when necessary? Is the noise floor low enough for this to look OK? Is there much in the way of unsightly fixed-pattern noise or is it beautifully random? 

Is there a way to make the highlights beautiful all the time? Maybe shooting ISO 800 would help as it would allocate more of the DR to the highlights while maintaining the maximum DR. (Thank you OleB for the chart)

Also, does "highlight recovery" in Resolve just not work with this camera? It often renders the highlights pink no matter what colorspace and gamma I use. In the waveform it looks like there still might be data there, however.

What are the best practices when it comes to grading the cDNGs from this camera in Resolve Studio? Timur Civan had a blog about using P3 D60 colorspace in Camera Raw, rather than Blackmagic Design. He then used a colorspace transform as a node in the color tab, I think. It went a bit over my head. What are people here using for colorspace settings in Resolve Camera Raw; P3 D60, or Blackmagic Design?

Thanks for your insights.

If you use the Rec709 based exposure preview, like the one the camera is able to show when you want to record cDNG, it is correct to assume that if you use ISO 800 you will get "better" highlight clipping. But that is only so because the camera in reality is underexposing 3 stops compared to ISO 100, leaving you with an ok looking image with 3 stops of additional highlight headroom compared to ISO 100.

In fact you are throwing quality away because you are lowering your exposure by 3 stops compared to what the real clipping value should be. This can only be shown with an external monitor which is able to record RAW, the process I have described above. But of course in that circumstance you have to be careful to not clip the highlights, because you are getting the best quality with the penalty that once they are gone, they are gone. Next to no safety margin.

To make highlight rolloff nicer I usually use Tiffen Black Pro Mist filters 😉 so that already takes place before recording.

But in the end it is up to you to decide which way is best. However I personally find it very much misleading that the camera behaves like this and correct exposure metering in camera is only possibly for ISO 100. In still mode however all is working like it should...

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11 hours ago, Owlgreen said:

Is there a way to make the highlights beautiful all the time? Maybe shooting ISO 800 would help as it would allocate more of the DR to the highlights while maintaining the maximum DR. (Thank you OleB for the chart)

In Resolve you can start to decode to P3-D60 and Linear in the RAW tab then do a "Color Space Transform" from the effects tab.  Transform to your timeline space, like REC709 Gamma 2.4 then check the box "use custom max input" under "Tone Mapping" and set it above your screen brightness like 250, 500, 1000.  You should see your highlights snap back and roll off nicely if they were available.  I wouldn't underexpose to try and get them if you are at ISO 800 because the shadows can block up. 

I usually do Noise Reduction in the first node, then CST in the 2nd node, then color and contrast correction in the 3rd with the lift gamma gain tools.

I attached two screen shots of the decode and CST. 

 

 

camera-raw-tab-DNG-DECODE.png

color-space-transform-rec709-gamma24.png

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