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Understanding Dual Gain ISO

  
 
snapsy
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p.1 #1 · p.1 #1 · Understanding Dual Gain ISO


I've published a video explaining what Dual Gain ISO is, why it's important, how to find the dual gain ISO level for your camera (using the Nikon Z6 III as an example), strategies for taking advantage of it, how it affects N-Log, and what the future holds for possible improvements. Although this video uses the Nikon Z6 III as an example, the concept applies to all cameras with dual gain ISO sensors, including other cameras from Nikon, Canon, Sony, etc...

To help make this technical subject easier to understand I use analogies and simplifications to the underlying mechanisms involved in dual gain ISO. If you'd like to dive deeper and gain (ahem) an even greater understanding of how sensors implement dual gain ISO I suggest reading the Aptina Dynamic Response Whitepaper on the subject, which Bill Claff hosts on his PhotonsToPhotos site:

https://www.photonstophotos.net/Aptina/DR-Pix_WhitePaper.pdf

Chapters in the video:

0:00 What is Dual Gain ISO?
2:44 How to find Dual Gain ISO level
5:46 ISO doesn't cause noise
6:40 Dual ISO shooting strategy
7:48 N-Log and Dual Gain ISO
8:22 Future: Dual ISO readout





Jul 09, 2024 at 04:41 AM
ilkka_nissila
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p.1 #2 · p.1 #2 · Understanding Dual Gain ISO


One issue with taking advantage of this knowledge is that Auto ISO is oblivious to the conversion gain and just applies its own logic, making the smallest change in ISO that allows correct exposure. I probably use Auto ISO for 99.9% of my shots ...

For astrophotography I would think it makes sense to use ISO 800 in this camera, as you want as much signal from weak light sources (nebulae) while it is difficult to avoid truncating some of the brightest stars, losing colour information if using very high ISO.

snapsy wrote:
I've published a video explaining what Dual Gain ISO is, why it's important, how to find the dual gain ISO level for your camera (using the Nikon Z6 III as an example), strategies for taking advantage of it, how it affects N-Log, and what the future holds for possible improvements. Although this video uses the Nikon Z6 III as an example, the concept applies to all cameras with dual gain ISO sensors, including other cameras from Nikon, Canon, Sony, etc...

To help make this technical subject easier to understand I use analogies and simplifications to the underlying mechanisms involved in dual
...Show more



Jul 09, 2024 at 05:23 AM
Nathan Padgett
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p.1 #3 · p.1 #3 · Understanding Dual Gain ISO


"Higher ISO doesn't increase noise"..... this is breaking my brain.

Also, I'd love to know the dual gain ISO's for each Nikon camera if anyone knows.



Jul 09, 2024 at 10:30 AM
tschopp
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p.1 #4 · p.1 #4 · Understanding Dual Gain ISO


Nathan Padgett wrote:
"Higher ISO doesn't increase noise"..... this is breaking my brain.

Also, I'd love to know the dual gain ISO's for each Nikon camera if anyone knows.


The photons to photos website is the easiest way of finding this.



Jul 09, 2024 at 10:38 AM
snapsy
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p.1 #5 · p.1 #5 · Understanding Dual Gain ISO


Nathan Padgett wrote:
"Higher ISO doesn't increase noise"..... this is breaking my brain.

Also, I'd love to know the dual gain ISO's for each Nikon camera if anyone knows.


Higher ISO actually modestly decreases read noise But the improvement is rather modest esp for ISOs above the dual-gain ISO and IMO not worth the cost in dynamic range vs shooting at the closet gain ISO (100 and 800 on the Z6 III for example).



Jul 09, 2024 at 10:50 AM
snapsy
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p.1 #6 · p.1 #6 · Understanding Dual Gain ISO


tschopp wrote:
The photons to photos website is the easiest way of finding this.


Yep. I meant to include this in my video but forgot.



Jul 09, 2024 at 10:50 AM
jaygould
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p.1 #7 · p.1 #7 · Understanding Dual Gain ISO


Since I learned about this (a few weeks ago), I only use ISO 100 and 400 now (where dual gain kicks in on my camera). There is no point in using anything else. It's better to lift the exposure in post. This way you avoid clipping the highlights.

ilkka_nissila wrote:
One issue with taking advantage of this knowledge is that Auto ISO is oblivious to the conversion gain and just applies its own logic, making the smallest change in ISO that allows correct exposure. I probably use Auto ISO for 99.9% of my shots ...


You can set your Auto ISO to begin wherever your camera's dual ISO kicks in. So then you have two choices:
1. 100 ISO
2. Auto ISO (for whenever you need anything more than 100. But it will skip all the ISOs below the dual gain point).



Jul 09, 2024 at 10:53 AM
Karl Witt
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p.1 #8 · p.1 #8 · Understanding Dual Gain ISO


Pretty darn amazing! And why don't we have dual gain on all sensors?

That was a great educational and at times well over my head video
Thank you Adam for a huge amount of time and research and data gathering to share, it makes sense, very very interesting for sure.
Karl



Jul 09, 2024 at 02:10 PM
RoamingScott
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p.1 #9 · p.1 #9 · Understanding Dual Gain ISO


This is certainly not a one size fits all method since AF relies on the brightness and contrast of the EVF feed. If youíre almost always shooting around 400 max though, itís a good thing to do.

jaygould wrote:
Since I learned about this (a few weeks ago), I only use ISO 100 and 400 now (where dual gain kicks in on my camera). There is no point in using anything else. It's better to lift the exposure in post. This way you avoid clipping the highlights.

You can set your Auto ISO to begin wherever your camera's dual ISO kicks in. So then you have two choices:
1. 100 ISO
2. Auto ISO (for whenever you need anything more than 100. But it will skip all the ISOs below the dual gain point).




Jul 09, 2024 at 02:29 PM
JBPhotog
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p.1 #10 · p.1 #10 · Understanding Dual Gain ISO


Nikon Z9 and Z8 dual gain ISO's are 64 and 500. Looks like the Z6 III is 100 and 800 so who knows what the upcoming Z7 III will be. I'd like to know if the Zf is also dual gain.


Jul 09, 2024 at 02:36 PM
 


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sputnik
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p.1 #11 · p.1 #11 · Understanding Dual Gain ISO


Iíve heard both 100 and 4000/6400 for the Zf, not sure if any of them are correct.


Jul 09, 2024 at 04:02 PM
RoamingScott
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p.1 #12 · p.1 #12 · Understanding Dual Gain ISO


ZF is 100/800


Jul 09, 2024 at 04:02 PM
AZHeaven
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p.1 #13 · p.1 #13 · Understanding Dual Gain ISO


Erik Durnall on the A7IV FB page had a video of the dual ISO of the A7IV. After testing he found the dual ISO of the A7IV to be 400 and 1600.


Jul 09, 2024 at 04:32 PM
snapsy
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p.1 #14 · p.1 #14 · Understanding Dual Gain ISO


You can find the dual ISO gain of any camera by visiting Bill Claff's PDR results page, clicking on a camera, then looking for the ISO on the graph that shows a noticeable increase in measured PDR. For example, here are his results for the Z6 III:

https://www.photonstophotos.net/Charts/PDR.htm#Nikon%20Z%206III



Jul 09, 2024 at 04:41 PM
KarmaKramer
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p.1 #15 · p.1 #15 · Understanding Dual Gain ISO


Lost me lol


Jul 09, 2024 at 05:00 PM
swifty168
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p.1 #16 · p.1 #16 · Understanding Dual Gain ISO


Karl Witt wrote:
Pretty darn amazing! And why don't we have dual gain on all sensors?

That was a great educational and at times well over my head video
Thank you Adam for a huge amount of time and research and data gathering to share, it makes sense, very very interesting for sure.
Karl


According to Bobn2 (a particularly knowledgeable poster in another forum), "Dual CV (conversion gain) usually reduces the maximum DR because it increases the read noise at low ISOs. Its use really is to extend the available DR at higher ISO settings"
But it appears the max DR reduction is fairly mild so the net results are very worth it, at least to me.

Also, the DR-Pix patent (that Snapsy linked to in the original post) is owned by Aptina, who has since undergone some ownership changes. Now, owned by ON Semiconductor I believe. There was apparently a patent swap with Sony Semi so Sony Semi definitely has access to it, as evident in many of their sensors. Who else has access, I'm not sure so there's the issue of licensing of the tech.



Jul 09, 2024 at 08:52 PM
sputnik
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p.1 #17 · p.1 #17 · Understanding Dual Gain ISO


RoamingScott wrote:
ZF is 100/800


Do you have a source for this? Not saying you are wrong but there are so many numbers flying around out there, and I would really like to know which number are the correct ones



Jul 10, 2024 at 03:34 AM
Massinissa
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p.1 #18 · p.1 #18 · Understanding Dual Gain ISO


sputnik wrote:
Do you have a source for this? Not saying you are wrong but there are so many numbers flying around out there, and I would really like to know which number are the correct ones


https://www.photonstophotos.net/Charts/PDR.htm#Nikon%20Z%20f



Jul 10, 2024 at 03:50 AM
Alistair1
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p.1 #19 · p.1 #19 · Understanding Dual Gain ISO


Good information, thanks for the good work. It's always nice to learn new things. Looking forward to the N-Log video for I did not understand the bit about analogue gain being applied in N-Log in addition to digital gain.

One day I will shoot a scene in reducing light with constant shutter speed and aperture and let ISO increase above 800 and see the difference in shadow noise between the shot just under 800 and the one just over 800.
The other exercise that would best indicate the practical use of this for me is if I shoot a scene in constant light with constant shutter speed, starting at (say) ISO400 whilst progressively reducing aperture to let auto ISO drift above 800 to maintain constant brightness in the image. Whether shadow noise in the first shot after ISO800 is better than any below ISO800.



Jul 11, 2024 at 02:25 AM
DanielJStein
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p.1 #20 · p.1 #20 · Understanding Dual Gain ISO


Love posts like this on this forum. I have been trying to educate my friends on how dual gain impact their shooting style as we are big on astrophotography. Good stuff here, especially the N-Log conversion. I had no idea how that worked.


Jul 11, 2024 at 06:32 AM
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