The base ("native") ISO of a sensor

In article ,
RichA wrote:

The Olympus E-M1 II has the lowest noise at ISO 64 (at the cost of a bit
less dynamic range) but the highest dynamic range at ISO 200. So what
would be the native or base ISO of the sensor?
How would that be defined?

The "base" would be the ISO where the analog and digital gain are both 1
(0 dB). I've never seen a camera maker publish that. The analog gain
stage is a noise source in itself - even at 0 dB - but unavoidable.

For my cameras (DSLR's) the base appears to be ISO 160 based on various
noise graphs. But frankly anywhere from 100 to 400 appears the same in
normal viewing. 800 and shadow noise is discernible in processing at
100% zoom but invisible in prints or display.

Although this post disputes what I wrote above - a lot to learn there.

http://www.clarkvision.com/articles/....summary/#unit
y_gain


One post here (by a noted astronomical CCD camera expert) says there is no
such thing as native ISO because there is amplification at every ISO.

http://www.tomsguide.com/forum/30791...-native-sensor

that's a thread from this newsgroup and the ccd camera expert is roger
clark, who used to post here and owns clarkvision.com and authored the
previous link.