Fully understood and agreed.
By "non native ISO" I was however also referring to ISO values such as 160 and 320, as these are pulled (similar to 50?) in contrast to eg. 125 which is claimed to be pushed.
I am trying to figure out if the inclusion of pulled ISO values make ETTR less useful
Sorry, I read your response as just relating to 'L' and 'H'; perhaps that's because I know about those !
I am not so sure of my facts with intermediate ISOs, but from what I do know, again you raise a very valid point.
If ISO 160 is
pulled from 200, ie it is just ISO 200 over exposed by one third of a stop and reduced back to 'correct' exposure in camera, then the same principle will apply. Conversely if 125 is
pushed one third from 100 the principle applies in reverse: you'd be already under exposing by one third so ETTR would have to be increased to compensate.
By the same principle ISO 160 would then have one third less EV latitude ( the dreaded DR ) than 200, but the test graphs don't show this.
But I am not sure of my facts on these 'non native' ISOs. I've read that people claim there is less noise at ISO 160 than 100, but I have not found this to be the case. However I have found that ISO 50 (L) can
give smoother data than 100.