@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?
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.
