Is extended ISO useless? A7sI has higher ISO than A7sIII?

[avalon]

Hello. Can someone explain to me what is the point of extended or boosted ISO? I read that only native ISO matters since it's based on hardware signal amplification and that extended ISO does nothing good other than to boost sales. I want to get a mirrorless camera that has similar low light sensitivity to mirrorless Sony A7s camera with very high ISO of 409,600. But Sony A7s mark II and III seem to have dropped native ISO just to 102,400 but extended ISO is 409,600. So I'm confused.

[Cameratose]

That sounds more like someone's opinion than it does a technical analysis, posted to get clicks. Extended ISO falls outside the analog range and is typically accompanied by in-camera NR. I wouldn't consider it useless. When I read something like that I consider the millions of people who are successfully using mirrorless cameras with those features every single day, then I shrug and ignore it. 

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[avalon]

I'm familiar only with hardware base, analog signal amplification. How how does (if it does) extended ISO make image brighter without resorting to longer exposure times?

[Cameratose]

Any increase in ISO is simply the camera's processor amplifying the signal. Sensors are designed to operate within a certain range, which is their 'Native' ISO. Extended ISO is simply further amplification of the signal beyond the native range, usually at the exponential expense of IQ loss and increased grain.

Contrary to popular belief, it does not make the sensor more sensitive to light, nor more able to absorb light. 

[avalon]

3 hours ago, Cameratose said:

Any increase in ISO is simply the camera's processor amplifying the signal. Sensors are designed to operate within a certain range, which is their 'Native' ISO. Extended ISO is simply further amplification of the signal beyond the native range, usually at the exponential expense of IQ loss and increased grain.

Contrary to popular belief, it does not make the sensor more sensitive to light, nor more able to absorb light. 

So oldest A7s mark I camera has best low light sensitivity and higher native ISO than later A7s mark III even when using BSI CMOS and is in fact most sensitive among all mirrorless camera's? Why Sony downgraded native ISO in A7s?

[Pieter]

Where did you get that the max ISO value of 409,600 on the original A7S is not an extended value? From what specs I can find, the original A7S has exactly the same native and boosted ISO range as the A7Siii. Anyway, for all practical purposes it doesn't matter anyway:

Sony cameras are pretty much ISO invariant, except for the base and second gain ISO levels. For the A7Siii shooting stills, it doesn't matter if you shoot at ISO 100 and raise exposure by 3 stops in post, or shoot at ISO 800. But at ISO 1600 the second gain kicks in and the noise clears up. From there on, it doesn't matter if you shoot at ISO 1600 and raise exposure by 8 stops in post, or shoot at ISO 409,600 (be it native or extended). All of this assuming you shoot RAW.

[FunWithCameras]

Extended ISO at the low end (eg: ISO "50" from a sensor with a native base ISO of 100) is overexposed - an image at ISO "50" is ISO 100 overexposed by a stop, with metadata saying "reduce the exposure by a stop when processing this RAW". There is some processing leeway - did you ever take an overexposed image and reduce the exposure when processing? The extended ISO does the same, and just like reducing the exposure in RAW processing, it loses some image quality.

Extended ISO at the high end underexposes the image, and then boosts it in RAW processing.

You are better off sticking to the native ISOs, and perhaps choosing to overexpose or underexpose for yourself (you can do it selectively using Ec.

I don't know where you got the impression that the original A7S had a native ISO up to 409600 - when I look up its specs they say native ISO goes from 100 to 102400 (with expanded ISO to 409600). Where did you find documentation saying otherwise?

[Cameratose]

7 hours ago, avalon said:

So oldest A7s mark I camera has best low light sensitivity and higher native ISO than later A7s mark III even when using BSI CMOS and is in fact most sensitive among all mirrorless camera's? Why Sony downgraded native ISO in A7s?

The top chart is DR for all three cameras. I guess if you want to call the A7S 'better' you can, but it's negligible up to 1600. It's tough to see the A7S blue triangles behind the others but 'extended' ISO ends at 419,000 and native is 102,000

But look what happens to Shadow Improvement on the SIII. It is 1/3 stop +/- better than either the A7S or SII from 1600 and up, where it counts, a product of newer sensor and processor. It's easy to see the SIII's dual gain amplification in both charts.

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[avalon]

7 hours ago, Pieter said:

Where did you get that the max ISO value of 409,600 on the original A7S is not an extended value? From what specs I can find, the original A7S has exactly the same native and boosted ISO range as the A7Siii. Anyway, for all practical purposes it doesn't matter anyway:

Wait, you mean that A7s mark I ISO of 409600 is not native?? I saw in multiple pages such as in camera comparison website cameradecision.com. Even Sony's official website states Ultra-high sensitivity of ISO 50 to ISO 409600.

https://cameradecision.com/compare/Sony-Alpha-A7S-III-vs-Sony-Alpha-A7S

https://www.sony.co.id/en/electronics/interchangeable-lens-cameras/ilce-7s#product_details_default

So if it's real native ISO is 102400 this changes things and there are plenty of camera's with the same native ISO.

Maybe newer sensor photosites utilise more space within the pixel itself or use some other unknown techniques to boost light gathering efficiency as well?

 

[Pieter]

20 minutes ago, avalon said:

Even Sony's official website states Ultra-high sensitivity of ISO 50 to ISO 409600.

Yea that's pretty misleading. Have a look here:

https://www.imaging-resource.com/PRODS/sony-a7s/sony-a7sDAT.HTM

But to be honest I don't really understand why you care so much about maximum ISO. Are you actually planning to shoot at ISO 102400 or even 409600, be it native or expanded? Because it will look dreadful anyhow and it really doesn't say anything about sensor sensitivity. If the A7S had native ISO 409600, it wouldn't look any better than a shot taken at 102400 boosted 2 by stops in post. Like @Cameratose said: 

Contrary to popular belief, it does not make the sensor more sensitive to light, nor more able to absorb light.

Edited September 16 by Pieter

[Cameratose]

19 minutes ago, avalon said:

Wait, you mean that A7s mark I ISO of 409600 is not native?? I saw in multiple pages such as in camera comparison website cameradecision.com. Even Sony's official website states Ultra-high sensitivity of ISO 50 to ISO 409600.

https://cameradecision.com/compare/Sony-Alpha-A7S-III-vs-Sony-Alpha-A7S

https://www.sony.co.id/en/electronics/interchangeable-lens-cameras/ilce-7s#product_details_default

So if it's real native ISO is 102400 this changes things and there are plenty of camera's with the same native ISO.

Maybe newer sensor photosites utilise more space within the pixel itself or use some other unknown techniques to boost light gathering efficiency as well?

 

Look at the charts I posted. It is clearly not native. 

[avalon]

3 hours ago, Pieter said:

Yea that's pretty misleading. Have a look here:

https://www.imaging-resource.com/PRODS/sony-a7s/sony-a7sDAT.HTM

But to be honest I don't really understand why you care so much about maximum ISO. Are you actually planning to shoot at ISO 102400 or even 409600, be it native or expanded? Because it will look dreadful anyhow and it really doesn't say anything about sensor sensitivity. If the A7S had native ISO 409600, it wouldn't look any better than a shot taken at 102400 boosted 2 by stops in post. Like @Cameratose said: 

Contrary to popular belief, it does not make the sensor more sensitive to light, nor more able to absorb light.

Yeah, I see other people being surprised by my need for high ISO but I need it. There is less known benefit of camera's such as A7s that they be used as night vision device especially after full spectrum conversion and using faster prime lens. I could see fields lit by just stars alone and didn't use best lens! What kind of other photo camera is capable of that As it helps to see subject in the darkness and AF works better. Also high sensitivity camera's also have very high dynamic range. Videos look amazing and sometimes you need to film sublects in low light even if takes getting noisier material. Also there are plenty of ways denoise photos/videos.

Edited September 16 by avalon

[Andrew3627]

Extended ISO at the low end (eg: ISO "50" from a sensor with a native base ISO of 100) is overexposed - an image at ISO "50" is ISO 100 overexposed by a stop, with metadata saying "reduce the exposure by a stop when processing this RAW". There is some processing leeway - did you ever take an overexposed image and reduce the exposure when processing? The extended ISO does the same, and just like reducing the exposure in RAW processing, it loses some image quality.