I made a simple test with my IQ180: 3 exposures
- at ISO 35
- at ISO 35 1.5 stops underexposed (= exposed like ISO 100)
- at ISO 100
If I open the files in ACR and add 1,5 stops exposure to the second picture, I see the following:
- the three pictures look very similar, but
- the second and third are more grainy in medium and dark areas
so my conclusion would be that the IQ180 is
- ISO 35 native* (not ISO 100 like Void suggests)
- up to ISO 100 in reality also ISO 35, just underexposed and already compensated by Phase RAW firmware (which means the picture looks correct exposed if opened in ACR or C1, just raw digger and similar raw programs can detect), but has reduced DR compared to shot at ISO 35
- above ISO 100 basically the same like below, means the real sensitivity is 1,5 stops lower than read on the back and internally compensated (which of course reduces the DR)
End of the story: Shoot ISO 35 wherever possible to get the 13.5 steps DXO-DR (acc. my experience up to 8s exposure time, then degration of file quality), then maybe still stay at ISO 35, underexpose and push in RAW conversion .
* I also read the enclosed DXO measurement of ISO sensitivity that way