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SIGMA FP with ProRes RAW and BRAW !


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19 minutes ago, Chris Whitten said:

What about 3200?

Neither. That's the problem. If you expose according to meters at 3200, you're actually two stops under. You will only see that when you import the CinemaDNG footage into Resolve. And "Profile off" doesn't help with that or change it in any way, unfortunately.

That's why I wrote that we're talking past each other.

The only workaround is to set the camera to ISO 800, meter, and then crank ISO up to 3200 while leaving aperture and shutter speed unchanged. But then you have a 2 stops overexposed camera display, no matter whether you're internally or externally monitoring. That's why I said that a custom LUT that pushes down external HDMI monitor display by 2 stops might be a workaround (but not really, since everything that will be clipped in the ISO 3200 preview display will still remain visually clipped.)

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13 hours ago, rawshooter said:

The problem is that at no ISO except 100, the camera will correctly meter 15% grey... There is no internal false color, but even the external false color of a field monitor will be wrong because the camera sends out an HDMI signal with gain baked in on all ISOs except ISO 100. So the only workaround would be a monitor LUT that reverses that baked-in gain...

BTW I meant 18% grey, couldn't edit my message. Yes I'm talking about if you had an external monitor with false color plugged in. Which kind of disrupts the minimalist design vibe.

This baked in ISO doesn't sound like an issue. If you're measuring false color from a grey card with baked in gain from the HDMI then that's what you want as a preview of where the metadata will place the ISO in post. At least to show the "intent". For example the D16 is ISO invariant with the DNG, but when you increase the ISO it reflects that in the log image sent over HDMI. Is that any different to this?

But I did also consider the idea of just shooting at 100 and having different LUTS with +1 stop increments instead. Could be worth a shot. Usually I do this anyway, but just +1 and -1 under/over the current exposure.

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15 hours ago, Chris Whitten said:

Another thread was created a while ago for a deep dive into FP colour management and codecs:

I think it was felt (not me by the way) that the Sigma FP thread was descending into microscopic detail rather than a general discussion of the camera in this thread.

I'm not a professional cinematographer or delivering content to a public broadcaster other than Instagram and Youtube, however I've shot a lot of CDNG on the FP inside and out and have yet to find a problem with the exposure. I've tried several different processes in Resolve and they mostly end up with pleasing looking footage, without any obvious colour shift, artefacts or issues. You can process this CDNG very quickly and get fantastic results.

That's not to say those with a technical eye or who are doing this full time shouldn't look for best practices. just the tone this thread is again taking is that the FP has serious issues that are at the moment not solvable. 

personally I think it's very forgiving and pretty easy to use.

 

 

I personally agree that exposure is not really an issue. I'm used to using a light meter or a grey card and false color with the Digital Bolex or Fuji X-T3, and for the most part that can be done with the fp. Highlight clipping is more tricky though.

Sorry if the topic has been derailed. I was originally commenting on what the external raw recording may bring to the table as far as more accurate monitoring, and how that may relate to the "none" picture mode. If you want I can post on the other thread instead.

I did also mention that people are creating great images with this camera. I saw some of your gorgeous images. Regardless of its quirks when it comes to color workflow, it has a lot going for it. It just depends on the context. I work in film post production and so maybe I'm being too demanding as far as what I expect from this camera, but it seems close to usable in that context.

What I'm actually advocating is something much more simple and robust than the rather complex ideas that I see people posting using the log curves of other cameras, which are not necessarily technically accurate workflows anyway. But I understand people need to fill in workflow gaps.

 

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10 hours ago, rawshooter said:

Neither. That's the problem. If you expose according to meters at 3200, you're actually two stops under. You will only see that when you import the CinemaDNG footage into Resolve. And "Profile off" doesn't help with that or change it in any way, unfortunately.

That's why I wrote that we're talking past each other.

The only workaround is to set the camera to ISO 800, meter, and then crank ISO up to 3200 while leaving aperture and shutter speed unchanged. But then you have a 2 stops overexposed camera display, no matter whether you're internally or externally monitoring. That's why I said that a custom LUT that pushes down external HDMI monitor display by 2 stops might be a workaround (but not really, since everything that will be clipped in the ISO 3200 preview display will still remain visually clipped.)

Sounds like a hassle. I still don't totally get what you're saying when I compare to my own experiences shooting DNG with my D16, but  I won't argue with your experience on the fp before I actually try it out for myself. 😉 

This seems like another reason to shoot a grey card so you can bring the exposure in post back to where your intent is.

I think you're going to get clipping anyway. It's just how bad is it going to be. Because I think "profile off" is just taking a slice of the linear scene referred output from the sensor and then applying a rec709 curve (essentially a gamma correction). I'm guessing that the nominal 0-1 slice is based on what the ISO setting would peg 18% grey at (0.18 in linear floating point) and then take a 0-1 slice around that. So all the highlights above "1" would get thrown out. With a log curve designed for the full range of the sensor, they all get recorded in a normalised 0-1 space which can be reversed out later and thus offering a faithful preview of the raw image.

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6 hours ago, Llaasseerr said:

Sounds like a hassle. I still don't totally get what you're saying when I compare to my own experiences shooting DNG with my D16,

I'm trying to rephrase: The main problem is the camera's display/preview.

You can get around the metering problems by metering the first native ISO with camera setting ISO 100 and the second with ISO 800. But the problem is that at ISO 800 setting, the camera still records at its first native ISO. It only makes the jump when set to ISO 3200. Now when you set it to ISO 3200, there are only two options: rely on the camera's metering and be 2 stops underexposed (and effectively throwing away 2 of the 12 bits color depth), or keep the metering from ISO 800, but then having a camera display that is two stops overexposed, i.e. where all the highlights are clipped.

And that extends to HDMI monitoring, where the same clipped image is sent to the monitor. You literally won't see a lot of what you are recording when at ISO 3200 and having the camera correctly expose the image. 

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7 hours ago, Llaasseerr said:

 

What I'm actually advocating is something much more simple and robust than the rather complex ideas that I see people posting using the log curves of other cameras, which are not necessarily technically accurate workflows anyway. But I understand people need to fill in workflow gaps.

 

Yes, excellent. It would be great.

More disappointing to me is that Phase One has never supported any Sigma cameras in Capture One, so you end up using their generic DNG profile.

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9 hours ago, Chris Whitten said:

Yes, excellent. It would be great.

More disappointing to me is that Phase One has never supported any Sigma cameras in Capture One, so you end up using their generic DNG profile.

I seem to remember Sigma have an excellent photo developing app of their own?

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10 hours ago, rawshooter said:

I'm trying to rephrase: The main problem is the camera's display/preview.

You can get around the metering problems by metering the first native ISO with camera setting ISO 100 and the second with ISO 800. But the problem is that at ISO 800 setting, the camera still records at its first native ISO. It only makes the jump when set to ISO 3200. Now when you set it to ISO 3200, there are only two options: rely on the camera's metering and be 2 stops underexposed (and effectively throwing away 2 of the 12 bits color depth), or keep the metering from ISO 800, but then having a camera display that is two stops overexposed, i.e. where all the highlights are clipped.

And that extends to HDMI monitoring, where the same clipped image is sent to the monitor. You literally won't see a lot of what you are recording when at ISO 3200 and having the camera correctly expose the image. 

Okay, this is a workaround but could I for example just leave it at ISO 100 where the sensor DR is at the max (12.5 stops) then assuming I have an external monitor, just have a LUT that exposes it up to ISO 800 and shoot everything like that? I don't need high ISOs and I would use an ND. Or light appropriately if it's too dark.

So did you discover this through detective work? It does sound like Sigma have not thought through their exposure implementation with a consistent user experience across ISOs, and the camera needs further firmware updates.

Or in the case of not being able to implement log, a hardware refresh (not sure if I totally buy that, either. But I also don't see why they would lie).

Back to the original topic of the thread: hopefully there are alternative exposure monitoring workflows presented with the external raw recorders. I guess I would lean towards the Blackmagic video assist since I would use Resolve. I'm starting to see the videos filter in on Youtube but I'd like to see the actual settings available on the recorders.

 

 

 

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Edit:

If I understand you correctly then based on re-reading what you're saying, I don't see why it's an issue that at ISO 800 it records as if at ISO 100 since it's ISO invariant, unless you switch to ISO 3200.  Assuming when shooting @800 the display is ISO 100 +3 stops then that would be correct because my understanding with dual ISO cameras is that you can't shoot at a lower ISO once you switch to the higher native ISO.

So the fact you shoot at ISO 800 when it's set to 3200 and it's two stops over exposed makes sense. The way this is dealt with in say the Fuji X-T3 is that you can't shoot below the native ISO when in say HLG. Sigma should probably enforce a limitation in the next firmware update to avoid confusion.

I would probably only use ISO 100 aka below 3200 anyway, since it's the max 12.5 stops and I would just add lights if it's too dark.

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1 hour ago, Llaasseerr said:

Okay, this is a workaround but could I for example just leave it at ISO 100 where the sensor DR is at the max (12.5 stops) then assuming I have an external monitor, just have a LUT that exposes it up to ISO 800 and shoot everything like that? I don't need high ISOs and I would use an ND. Or light appropriately if it's too dark.

So did you discover this through detective work? It does sound like Sigma have not thought through their exposure implementation with a consistent user experience across ISOs, and the camera needs further firmware updates.

Or in the case of not being able to implement log, a hardware refresh (not sure if I totally buy that, either. But I also don't see why they would lie).

 

 

 

The second native ISO 3200 is there for a reason, and it would be a shame to not make use of the excellent low light capabilities of the camera.

I discovered this through exposing ETTR with the camera at ISO 3200, importing the footage into Resolve, and see that it was two stops underexposed. Even when the camera said that it was clipped with two stops over at ISO 3200, it turned out not to be clipped in Resolve (with highlight recovery turned off). So exposing at 2 stops lower (= ISO 800) gives you correct exposure for ISO 3200.

If you're 2 stops under, it means that you're throwing away 2 stops dynamic range and 2 bits of color depth.

The exposure implementation is typical, btw., for photo cameras and their focus on sRGB JPEGs. For sRGB JPEG/Rec709 non-raw movs, the camera's exposure indicators are correct. - Blackmagic, on the other hand, gives you correct raw exposure metering. Zebras are ISO-invariant in relation to the camera's native ISOs.

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1 hour ago, Llaasseerr said:

If I understand you correctly then based on re-reading what you're saying, I don't see why it's an issue that at ISO 800 it records as if at ISO 100 since it's ISO invariant, unless you switch to ISO 3200.  Assuming when shooting @800 the display is ISO 100 +3 stops then that would be correct because my understanding with dual ISO cameras is that you can't shoot at a lower ISO once you switch to the higher native ISO.

So the fact you shoot at ISO 800 when it's set to 3200 and it's two stops over exposed makes sense. The way this is dealt with in say the Fuji X-T3 is that you can't shoot below the native ISO when in say HLG. Sigma should probably enforce a limitation in the next firmware update to avoid confusion.

I would probably only use ISO 100 aka below 3200 anyway, since it's the max 12.5 stops and I would just add lights if it's too dark.

When you're recording at ISO 800, you're actually recording ISO 100 three stops underexposed, since ISO 800 is just ISO 100 pushed in software by three stops. (I.e. you get the same - identical - image if you dial down the camera to ISO 100 with the same aperture and shutter settings, have a totally underexposed image on the camera display, but later crank up the exposure slider in Resolve to +3).

The camera has two native ISO, declared as "100" and "3200" by Sigma - which is correct only in relation to a Rec709/sRGB gamma, but in terms of raw exposure really mean "100" and "800" or, more likely, "400" and "3200". (Actually ISO 100 on the fp is as bright/fast as ISO 400 on a Blackmagic Pocket 4K/6K - tested it myself, so ISO 100 is probably a misnomer.)

This is all legacy stuff for photographers, their working in sRGB, which in turn emulates slide film and the way people exposed film (as opposed to exposing ETTR). 

The real problem is that the camera doesn't have a Log profile. If Sigma had implemented a Log profile, it would also have had to adjust metering to it, probably resulting in the two native ISOs 400 and 3200 for Log, which automatically would have translated into correct exposure for RAW (since both Log and RAW capture the sensor's full dynamic range while Rec709/sRGB clips it).

 

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4 hours ago, rawshooter said:

When you're recording at ISO 800, you're actually recording ISO 100 three stops underexposed, since ISO 800 is just ISO 100 pushed in software by three stops. (I.e. you get the same - identical - image if you dial down the camera to ISO 100 with the same aperture and shutter settings, have a totally underexposed image on the camera display, but later crank up the exposure slider in Resolve to +3).

The camera has two native ISO, declared as "100" and "3200" by Sigma - which is correct only in relation to a Rec709/sRGB gamma, but in terms of raw exposure really mean "100" and "800" or, more likely, "400" and "3200". (Actually ISO 100 on the fp is as bright/fast as ISO 400 on a Blackmagic Pocket 4K/6K - tested it myself, so ISO 100 is probably a misnomer.)

This is all legacy stuff for photographers, their working in sRGB, which in turn emulates slide film and the way people exposed film (as opposed to exposing ETTR). 

The real problem is that the camera doesn't have a Log profile. If Sigma had implemented a Log profile, it would also have had to adjust metering to it, probably resulting in the two native ISOs 400 and 3200 for Log, which automatically would have translated into correct exposure for RAW (since both Log and RAW capture the sensor's full dynamic range while Rec709/sRGB clips it).

 

Your first paragraph is a given and I stated that myself so I'm not sure why you are rephrasing that back at me. Basically everything you're describing is the way I work shooting raw with the D16 except it's not dual ISO. But I do get predictable results. As for why the fp sensor is rated at 100 vs the BMD sensor at 400 for the same brightness, that's because they are completely different sensors and the manufactures rate them with different native ISOs based on their technology.

Your second paragraph I don't get.  I think you're trying to explain how the ISO readings differ based on whether you're looking at the rec709 preview vs what the raw exposure is? ISO values are always in linear, because they're based on the voltage of the sensor or in photographic terms it's the same, it's the doubling of light that means +1 stop brighter. This always happens in linear light and this is unambiguous. The sRGB/Rec709 curve is added afterwards for display, but it makes no difference.

sRGB has nothing to do with slide film or how film is exposed. It's an ancient display standard that is a gamma curve that compensates for the fact that gamma 1.0 images do not look correct and sRGB is a more efficient usage of what was traditionally only 8 bits to display tonal information. ETTR exposing is nothing but a workaround for people with more affordable digital video cameras that want to protect their highlights. With an Alexa you just expose for middle grey and the highlights come along for the ride.

Sigma would not need to adjust the metering if the camera had a log profile. Metering is done in linear light values, ie. in digital terms "scene referred gamma 1.0". All log encoding does is that it changes exposure adjustment into an additive operation instead of a multiplication operation.  Log is just an encoding method that is very efficient and creates uniform code values between stops. A pure log curve is ACEScc.

It doesn't sound to me like Sigma are doing anything wrong except maybe there are a few rough edges.

 

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5 hours ago, rawshooter said:

The second native ISO 3200 is there for a reason, and it would be a shame to not make use of the excellent low light capabilities of the camera.

 

The exposure implementation is typical, btw., for photo cameras and their focus on sRGB JPEGs. For sRGB JPEG/Rec709 non-raw movs, the camera's exposure indicators are correct. - Blackmagic, on the other hand, gives you correct raw exposure metering. Zebras are ISO-invariant in relation to the camera's native ISOs.

Yeah it sounds like a goood feaature to have.

Quote

If you're 2 stops under, it means that you're throwing away 2 stops dynamic range and 2 bits of color depth.

But adjusting a raw image +/- 2 stops with an ISO invariant sensor is a lossless operation, so what makes you think that? I routinely shoot -2 stops to protect highlights and I sanity check it with a light meter. Generally I use an ND to go down -2 stops in that case though. You don't lose 2 stops, it's just a trade off whether you get noisy shadows or clipped highlights. I'd rather have noisy shadows because I like the texture and I can always degrain a bit, vs not getting the highlights at all.

Again, I might be missing something specific about this camera. If so then sorry about that. I'll just have to try it out to get what you're saying. I would never use zebras to adjust exposure. I know the S1H has a built in luminance spot meter mode for checking exposure based on 18% grey. That's more appropriate IMO. 

Internally, cameras that save sRGB JPEGs are still metering in linear light. 

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Just stepped away for a sec and it occurred to me maybe you're saying that checking zebras in log is helpful for checking sensor clipping. If so, then yes I agree because the sensor DR should be normalised to 0-1 space in a log display, if the log curve encompasses the entire DR of the sensor.

I say "if", because in my tests the Fuji F-log max linear value before encoding to log is below the X-T3 sensor clipping point, which is why I use HLG because it's more generous.

It's a bit annoying needing to toggle back and forth between log and your display LUT, but yeah it's a workable option.

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  • 3 weeks later...
6 hours ago, Chris Whitten said:

New L mount lens, 85mm.

That said, native L mount lenses IMHO have zero advantages - I'd even say: only disadvantages - over adapted manual lenses when one uses the Sigma fp for video:

  • autofocus and auto-iris aren't meaningfully usable in video mode;
  • focus-by-wire sucks;
  • so far, all Sigma "DC" lenses rely on geometric correction in software, which doesn't work with RAW video.
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Yep.

I'm in all manual mode when shooting video. I would like a native Sigma lens just as an option for stills. At the moment I have the bulky loupe attached. And manual focussing is sometimes slow. Probably the smallest usable set up is the body and the 'kit' lens.

The body and Leica M 35mm f2 is much smaller, but I need the loupe to focus.

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