So my question is; does anyone know the ISO S/N curve for the S2 (and M9 for that matter)? At what point does the ISO amplification begin to degrade the S/N ratio? Or is it like the Exmoors and it really doesn’t matter what ISO you set it to as long as it isn’t too high. Making it essentially an “ISO-less” camera
The sensor-type (CMOS or CCD) is more relevant for the noise-type than the processor. Leica uses CCD-sensors that have other characteristics than CMOS used in 35 mm DSLR.
And even with CMOS-sensors the noise is increasing with higher ISO, but not as sharp as with a CCD.
Compared, for example, and starting wirh 100 ISO, the S2 behaves almost the same at 200, 400 iso, compared to a Nikon D3x, the spread increases rapidly from 640 ISO upwards. I would say from experience that 800 ISO with the S2 compares to 1200-1600 ISO on the Nikon D3x (and maybe 3200-6400 ISO on a D3S).
Also, resolution and post-processing is an important factor.
btw, ISO-Quality is not a question of S/N-ratio, it is more a stastistical problem of missing and eraticcal data. This is why a CCD-sensor with a lot of pixels can be as good as a CMOS-sonsor with less pixels (up to a certain level, though).