Beginner Low iso noise?

[SsSsSsSsSnake]

when dxo for eg review sensors they talk about low iso noise and how certain cameras dont catch up till say 400 iso.
Can someone explain,i thought lower iso gives less noise? How can raising iso give lower noise?
Thanks

 

[Pookeyhead]

It doesn't mean they have less noise at higher ISO. It means that some cameras have better noise levels at 100, but get worse, faster.... for want of a better way of putting it.

 

[Kodiak Qc]

•
The chip is the chip, it remains what it is but it has nominal characteristics.

One of them is its nominal sensibility to light, expressed in ISO. The onboard
software may extend the relative ISO to a given point without generating noise,
say +/- 2000 ISO. So, from its nominal sensitivity to the software extended one,
there should be no noticeable noise —given the exposure is correct.

Over the extended capacity of the software, noticeable noise will be generated
because information, data, must be recorded where not enough input is available.
What DXO is referring to is the "extended relative ISO", which is the maximum
noiseless ISO value in a given camera —some are better then others, like my
D3S and the D4/S, known as low-light champions.

 

[SsSsSsSsSnake]

thanks both

 

[archstanton]

As a practical example, stick your camera on a tripod and take a photo with the night sky in it - even locked at ISO100 you'll see more noise in the dark sky on some cameras than on others.