Is extended ISO just useless marketing trick? Closest Canon mirrorless camera to Sony A7s?

[Zalkonian]

Hello. Can someone explain to me what is 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 Canon camera that has similar low light sensitivity to mirrorless Sony A7s camera with very high ISO of 409,600 and big pixels making it great for astrophotography and videography. But Sony A7s mark II and III seem to have dropped native ISO just to 102,400 but extended ISO is 409,600. So that makes me wonder if extended ISO has any practical use to it?

[johnrmoyer]

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@Zalkonian wrote:

Hello. Can someone explain to me what is extended or boosted? 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 Canon camera that has similar low light sensitivity to mirrorless Sony A7s camera with very high ISO of 409,600 and big pixels making it great for astrophotography and videography. But Sony A7s mark II and III seem to have dropped native ISO just to 102,400 but extended ISO is 409,600. So that makes me wonder if extended ISO has any practical use to it?

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It is more complicated than "only native ISO matters" for modern sensor chips. Some sensor chips have more than one path from photosite to A2D converter and so have more than one possible gain level and more than one native ISO. Dual pixel sensors have twice as many photosites and so have more options for creating a raw file from the measured data. A newer generation of sensor chip will be able to achieve a higher ISO with the same noise level. Larger photosites can collect more photons in the same exposure time traded off by lower resolution.

For low light scenes where nothing is moving, a long exposure followed by subtraction of a dark frame at low ISO is usually better than high ISO, but that cannot be done with video. If the camera is able to downsample with noise reduction to make video, that might make a much higher ISO practical.

Advice: look for high ISO example images from the cameras one wishes to compare and consider differences in resolution.

[Zalkonian]

Such as? Dual pixel sensors as I understand are used in Canon camera's for better autofocus. Maybe you meant dual gain sensor?

[johnrmoyer]

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@Zalkonian wrote:

Such as? Dual pixel sensors as I understand are used in Canon camera's for better autofocus. Maybe you meant dual gain sensor?

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While this has advertising for a software product, it also has an easy to read explanation of digital gain and ISO. https://www.rawdigger.com/howtouse/iso-is-seldom-just-digital-gain

This link is to a paper that contains a schematic for a photosite on a dual gain sensor with a comparison to single gain. https://www.imagesensors.org/Past%20Workshops/2019%20Workshop/2019%20Papers/R06.pdf

A sensor may be both dual gain and dual pixel. Modern high end cameras have enough processing power to use more complex algorithms when creating the raw file than simply recording the output from the analog to digital conversion. For dual pixel, the two pixel halves might be just added together or might be compared to other pixel halves to for example increase sharpness or modify portrait lighting. This processing might be delayed until later if the dual pixel data is saved. For example in a camera manual there is a description of processing a dual pixel raw file in camera to improve portrait lighting or to increase clarity: https://cam.start.canon/en/C003/manual/html/UG-05_Playback_0200.html 

For example, a camera with dual pixel data and enough computer processing power might implement a "fine detail" menu setting by doing the image clarity dual pixel raw processing before saving a raw file that does not contain the dual pixel data. The camera sometimes has more information than is saved in the raw file.

[Zalkonian]

What mirrorless photo camera's are using dual gain DGO sensor technology? I can find only Canon video camera's with low resolutions using it. Sony A7s uses dual gain too.

Does pixel binning offer significant sensitivity boost in mirrorless camera?

[kvbarkley]

While there might be some tricks going on behind the scenes, I think Extended ISO modes are ones that yield a lot of noise - more than what the mfg considers "acceptable" in a base camera. I.e., extended ISO are "use at your own risk" kind of modes, or as you say, marketing.

Since you have such specific needs, I suggest you rent one to try it out.

We can't answer your question without knowing how much noise you consider acceptable.

[Zalkonian]

Noise is acceptable to me at very high ISO. So far Canon EOS R6 seemed to be most attractive action to me but after seeing that doesn't utilise backlit BSI CMOS I lost interest in it. Canon EOS R6 II also doesn't use it? I read that cooling sensor helps to reduce noise but are there mirrorless camera's with them?

Why Canon mirrorless photo camera's don't use dual gain technology?

[wq9nsc]

Active cooling is used in some of the specialized astronomy cameras intended for very long exposure however that isn't practical for a general use camera because of the significant power used for cooling.  I have an astronomy camera and its anti-dew heater and sensor cooler are powered by an external "brick" separate from the main camera power source.  Power consumption is already an issue with the mirrorless platform and adding additional drain would require the use of an external power source.

And the most typical method of cooling uses forced air cooling as at least part of the cooling system which isn't useful where a system needs to be weather sealed or at least highly weather resistant.  Otherwise if you wanted a sealed system then you would need a Peltier type cooler using the external surface of the camera as a heat sink which isn't practical.

I shoot primarily sports and have used quite a few images from my 1DX III bodies in the ISO 40,000 range and this was with no other NR than that provided within Canon's DPP software.  But I wouldn't use an ISO anywhere close to that level for more critical images such as senior night presentations.

Typically in HS football, the darkest areas are the end zone and much of the sidelines and the following 2 images (ISO 32,000 and 51,200 respectively) were with one of my 1DX III bodies and are from a post-season playoff game in the rain adding to the "fun" of the event with the temp at 36F.  The last two images were from when I was curious about ISO performance when I bought my first 1DX III camera body, you can recognize the image is a cat but I wouldn't likely use an image of the quality of this one at the ISO 102,400 level and I would only use ISO 819,200 (the last image) if I was searching for my cat in the dark 😂

Rodger

[kvbarkley]

We are just users, we can only speculate about Canon engineering decisions. You can look for a white paper, but most that I find are video-centric.

[Zalkonian]

I was dissapointed to learn that Canon R6 doesn't use BSI CMOS sensor despite being released recently, after 2020. Does Mark II and other lower megapixel models use BSI CMOS?