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Exposure Indexing on A7SII Sony Cameras?


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Hey There!

To keep this super simple I've been shooting so much Sony (FS7, FX9) for so long that I've kinda gotten entirely confused about how other cameras expose and if it's an identical premise or entirely different.

When shooting Sony in Cine EI mode you have a Base ISO and you decide to let in more or less light to get your desired EI (Under or over) and you decide how to push and pull it in post or in-camera and I heavily assume Alexa, is the exact same premise.

But how do these methods change when playing with an A7SII for example that doesn't have dedicated Cine EI mode even Canon? I know that no matter your ISO your DR/Stop allocation will not change unless you physically under-expose or over-expose, Is the Cameras like an A7SII Base ISO or more like a technically "Best" ISO but you can pick any want to use as your base, just you, of course, Introduce noise.

Thanks

-Samuel

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FX3 has that Cine EI mode now!  Maybe worth switching if you really like that way of handing exposure.

The way the Alexa handles ISO (when using the prores log workflow):  you are adjusting the post AD conversion processing of the image.  When you raise the ISO, you are lifting darker values up to middle gray.  When you decrease ISO, you're dropping brighter values down to appear as middle gray.  But your highlight and shadow clipping isn't changing because the sensor has innate light gathering properties.

The way I like to think about the Alexa is I'm using ISO to choose how many stops above middle gray I have and how many stops below.  If you stick at the base of 800, you have roughly 7 up and 7 down.  If you increase one stop to 1600, you have 8 up and 6 down.  I like to increase my ISO - I like the added texture in the image and I like the camera to behave a bit more like film which has more latitude in the highlights than shadows.

If you really get into it, this is a bit of a simplification with the Alexa - there are two gains applied in parallel and recombined in the same frame.  So I'm sure there's a little bit more going on under the hood when you increase ISO.

 

I haven't tested my FX3 out since upgrading the firmware but I'm a bit skeptical about the Cine EI mode on that camera.  The 10 bit recording plus built in noise reduction could be a bottleneck with the DR.  I have a feeling that at the higher ISOs (per base ISO) perform better when you let the camera do the processing.  I'll have to shoot some side by sides to confirm though.

I suspect the main reason they have added the option for Cine EI mode is to make multi-camera workflows simpler where you're mixing FX3s, FX6s, and FX9s

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17 hours ago, Dan Finlayson said:

FX3 has that Cine EI mode now!  Maybe worth switching if you really like that way of handing exposure.

The way the Alexa handles ISO (when using the prores log workflow):  you are adjusting the post AD conversion processing of the image.  When you raise the ISO, you are lifting darker values up to middle gray.  When you decrease ISO, you're dropping brighter values down to appear as middle gray.  But your highlight and shadow clipping isn't changing because the sensor has innate light gathering properties.

The way I like to think about the Alexa is I'm using ISO to choose how many stops above middle gray I have and how many stops below.  If you stick at the base of 800, you have roughly 7 up and 7 down.  If you increase one stop to 1600, you have 8 up and 6 down.  I like to increase my ISO - I like the added texture in the image and I like the camera to behave a bit more like film which has more latitude in the highlights than shadows.

If you really get into it, this is a bit of a simplification with the Alexa - there are two gains applied in parallel and recombined in the same frame.  So I'm sure there's a little bit more going on under the hood when you increase ISO.

 

I haven't tested my FX3 out since upgrading the firmware but I'm a bit skeptical about the Cine EI mode on that camera.  The 10 bit recording plus built in noise reduction could be a bottleneck with the DR.  I have a feeling that at the higher ISOs (per base ISO) perform better when you let the camera do the processing.  I'll have to shoot some side by sides to confirm though.

I suspect the main reason they have added the option for Cine EI mode is to make multi-camera workflows simpler where you're mixing FX3s, FX6s, and FX9s

Thanks so much for your response.

So Cine EI though works the same as an Alexa in LogC?

FX9 you can shoot slog3 with an slog3 LUT, expose at a EI of 1600 and gain a stop extra in the highlights at the cost of noise and a stop less in shadows because you are essentially under exposing the footage and in that case correcting in camera rather than in post, same for the Alexa?

Just wanted to clarify that is the same for both cameras.

 

Edited by Sam Bignell
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On 7/19/2022 at 3:20 PM, Sam Bignell said:

So Cine EI though works the same as an Alexa in LogC?

My understanding of Cine EI mode is that changing the ISO in camera changes the brightness of the EVF/monitor outputs and adds a metadata tag for post.  But the actual ISO change is effectively being done on your computer.

So the concepts are very similar - with the Alexa you are baking your choice in on set (with prores) and with the Sony system you are still free to deviate from your on set choice later.  I believe this is the case with both raw and non-raw options on the sony cameras.  So a slight difference there - which could hurt the Sony cameras performance in the non-raw version of this.

I'm anticipating better results with my FX3 when I bake the ISO choice in on set versus shooting at 800 exactly all the time but we will see.

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5 hours ago, Dan Finlayson said:

My understanding of Cine EI mode is that changing the ISO in camera changes the brightness of the EVF/monitor outputs and adds a metadata tag for post.  But the actual ISO change is effectively being done on your computer.

So the concepts are very similar - with the Alexa you are baking your choice in on set (with prores) and with the Sony system you are still free to deviate from your on set choice later.  I believe this is the case with both raw and non-raw options on the sony cameras.  So a slight difference there - which could hurt the Sony cameras performance in the non-raw version of this.

I'm anticipating better results with my FX3 when I bake the ISO choice in on set versus shooting at 800 exactly all the time but we will see.

The FX9 you can run a "Slog3 Lut" which will physically show you the exposure changes of your ISO and you can record that into the footage meaning it will actually burn in the ISO changes all while still being your plain flat Slog3 profile.

I was curious if both cameras acted very similarly to the way they work around their base ISO but seem they do which is just nice to know knowledge-wise!

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15 hours ago, Sam Bignell said:

you can record that into the footage meaning it will actually burn in the ISO changes all while still being your plain flat Slog3 profile

Ah interesting!

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My understanding is that the A7 series has "analogue ISO", using an amplifier between the sensor and the DAC, like most DSLR. Then the philosophy of changing the ISO to modify the stops allocation above/below middle gray - keeping the same overall DR - does not apply. With analogue ISO, you basically loose one stop of overall DR each time you raise the ISO one stop. You cannot raise the ISO to protect the highlights either. The culprit is not the sensor, but the DAC.

Some DSLR allow to trade one or two stops of analogue amplification for the equivalent digital amplification. On that very limited range, they do work like a "regular" cinema camera. I do not know for the A7S2.

There are advantages to the analogue ISO (otherwise nobody would use it): better low light performance and no risk of banding due to the quantization step being too rough.

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17 hours ago, Nicolas POISSON said:

My understanding is that the A7 series has "analogue ISO", using an amplifier between the sensor and the DAC, like most DSLR. Then the philosophy of changing the ISO to modify the stops allocation above/below middle gray - keeping the same overall DR - does not apply. With analogue ISO, you basically loose one stop of overall DR each time you raise the ISO one stop. You cannot raise the ISO to protect the highlights either. The culprit is not the sensor, but the DAC.

Some DSLR allow to trade one or two stops of analogue amplification for the equivalent digital amplification. On that very limited range, they do work like a "regular" cinema camera. I do not know for the A7S2.

There are advantages to the analogue ISO (otherwise nobody would use it): better low light performance and no risk of banding due to the quantization step being too rough.

This is my knowledge on it also but... Here's a big questions.

How does this differ then to just taking one of them cameras, putting it at 800 ISO and then treating that as your single and only base ISO (All cameras still have a base) then push and pull via luts and in post treating like Cine EI?

The result is the same as an official Cine EI mode surely?

Only you can still physically add ISO gain.

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14 hours ago, Sam Bignell said:

How does this differ then to just taking one of them cameras, putting it at 800 ISO and then treating that as your single and only base ISO (All cameras still have a base) then push and pull via luts and in post treating like Cine EI?

I'm sorry, I miss-read originally and was thinking A7SIII not A7SII.  Nicolas is correct, especially with the mark II.

I think it's hazier with the mark III and more so with the FX3.  They still have analogue gain of course.  But in my experience so far, it's way better to let the camera handle gain and specifically noise reduction when you're more than 2 stops from either base exposure.  You may maintain more stops at 800 but if you amplify the noise so much in post that the bottom stops aren't useful, it's a wash...  if that make's sense.

I've been swamped but I'm hoping to shoot a test this week to demonstrate what I'm describing...  or prove myself wrong!  We'll see

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9 hours ago, Dan Finlayson said:

I'm sorry, I miss-read originally and was thinking A7SIII not A7SII.  Nicolas is correct, especially with the mark II.

I think it's hazier with the mark III and more so with the FX3.  They still have analogue gain of course.  But in my experience so far, it's way better to let the camera handle gain and specifically noise reduction when you're more than 2 stops from either base exposure.  You may maintain more stops at 800 but if you amplify the noise so much in post that the bottom stops aren't useful, it's a wash...  if that make's sense.

I've been swamped but I'm hoping to shoot a test this week to demonstrate what I'm describing...  or prove myself wrong!  We'll see

I would be really interested to know the results because I don't quite see how a high-end FX9 in Cine-EI mode actually differs from an FX3 not in Cine-EI mode, if you treated both cameras exposure in post would there be any real difference?

In my head, the Camera with analogue gain sounds like a win in both because it can theoretically push further into higher ISO's while technically maximizing Dynamic range as your stops don't shift around middle grey, only noise will affect your stops in the shadows.

To my preference, I prefer the Cine-EI modes but an analogue gain sounds like a win in both but there must be more to this.

Edited by Sam Bignell
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A big plus for the new Cine EI in the fx3 V2 , is you can use LUT,s  , before you couldn't , only Gamma assist in the EVF , you can also out put the LUT over HDMI. And the base ISO has gone to 800 (like the fx6/9) from 640 (in the cine EI modes anyway) .. you can still shoot slog3 in the PP mode and add actual gain as before , or just over expose it , but Cine EI is just a much better way of setting an exposure off set (over or under ) .. and I agree with the previous poster , its to bring the fx3 better inline to working with the fx6/9 as they very often are used as a B / gimbal camera . I use mine with an fx9 like this, and very happy for the introduction of Cine EI, V2 also gives you a much clearer EVF in movie mode , which might actually be the biggest advantage .. now all we need is variable shutter ..!

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54 minutes ago, Robin R Probyn said:

A big plus for the new Cine EI in the fx3 V2 , is you can use LUT,s  , before you couldn't , only Gamma assist in the EVF , you can also out put the LUT over HDMI. And the base ISO has gone to 800 (like the fx6/9) from 640 (in the cine EI modes anyway) .. you can still shoot slog3 in the PP mode and add actual gain as before , or just over expose it , but Cine EI is just a much better way of setting an exposure off set (over or under ) .. and I agree with the previous poster , its to bring the fx3 better inline to working with the fx6/9 as they very often are used as a B / gimbal camera . I use mine with an fx9 like this, and very happy for the introduction of Cine EI, V2 also gives you a much clearer EVF in movie mode , which might actually be the biggest advantage .. now all we need is variable shutter ..!

Could not agree more, it's a much-needed update however I'm not giving points to sony because it's one that should have been in the camera from the start, Shutter's angle would be truly great but I'm certainly not going to hold my breath for it.

 

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2 hours ago, Sam Bignell said:

Shutter's angle would be truly great but I'm certainly not going to hold my breath for it

Shutter angle would be nice but speaking of breath - I want that lens focus breathing compensation from the A7IV way more

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2 hours ago, Sam Bignell said:

Could not agree more, it's a much-needed update however I'm not giving points to sony because it's one that should have been in the camera from the start, Shutter's angle would be truly great but I'm certainly not going to hold my breath for it.

 

Shutter angle I dont care about , its often easier to calculate non flicker shutter by speed , and it all looks the same anyway , what I what is variable shutter , like the larger cameras have had for many years , it can really save the day . Its a risk for anyone shooting with fx3 as their only camera on an un recced location ..

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On 7/25/2022 at 5:17 PM, Sam Bignell said:

In my head, the Camera with analogue gain sounds like a win in both because it can theoretically push further into higher ISO's while technically maximizing Dynamic range as your stops don't shift around middle grey, only noise will affect your stops in the shadows.

Analogue gain is not a win-win. I try to explain with my own words (not very scientific).

Take some camera with analogue gain that can capture 12 stops of DR at a base ISO of 100. That camera will only be able to capture 11 stops at ISO 200, 10 stops at ISO400, and so on. I am assuming the ADC (not DAC, sorry) clipping threshold fits the full well capacity (FWC) of the sensor at base ISO of 100 (say the manufacturer has set the analogue gain at ISO 100 in that purpose). If you double the gain, now the ADC clipping threshold corresponds to half the FWC of the sensor. If you double the gain one more time, the ADC clip is 1/4 of the FWC. The DR of the sensor never changes, but the overall DR of the chain [sensor + gain + ADC] halves each time you double the ISO. You loose DR when raising the ISO on such a camera, even if you shoot RAW. There are some tricks with dual-ISO or similar, but the "ISO x 2 = DR / 2" rule is the trend you can see in almost all Bill Claff"s measurements, since DSLRs are using analogue gain:

https://www.photonstophotos.net/Charts/PDR.htm#Canon EOS 5D Mark IV,FujiFilm X-T4,Panasonic Lumix DC-GH5,Sony ILCE-7M2

If you set your analogue gain camera at ISO 800 and then push/pull exposure with LUTs, yes this is similar to digital gain (the LUT does it). But you start with a DR reduced by 3 stops in the highlights compared to ISO 100, at 9 stops. If you were using a camera with digital gain, the overall DR would remain unchanged at 12 stops.

However, one could define two DR:

- the ratio between the highest luminance the device could get and the noise. Let's call it "peak DR".

- the ratio between the actual average luminance of your scene and the same noise. Let's call it "avg DR"

On analogue gain cameras, peak DR halves as ISO doubles. On digital cameras, peak DR remains unchanged whatever the ISO. However, the "greatest DR you could capture" is not the "actual DR of your scene". Imagine your highlights are 3 stops above the average luminance of your scene. Having 5 stops of DR above middle grey is useless: the two highest stops are unused. Yes the camera could capture more DR, but your scene does not have more DR to be captured.

The evolution of avg DR depends of the main source of noise. If the noise mainly comes from the camera electronics, then analogue gain performs better than digital gain. Raising the ISO improves the avg DR on analogue cameras, but does nothing on digital gain cameras. This is due to the fact that the signal-to-noise ratio of an analogue amplifier improves at higher gain. That is one good reason to use analogue gain (the other one being ADC quantization step). If the noise mainly comes from the inherent randomness of light (photon noise), typically in very low light conditions, then the avg DR is equal at any ISO, whether analogue or digital ISO. The only way to improve avg DR is to fill the shadows with more light in the real world.

That is very simplified. Cameras use de-noising techniques, which can artificially improve DR and may perform differently depending on analogue or digital gain. I do not know.

Edited by Nicolas POISSON
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