Nikon D3S High ISO RAW
Nikon D3S RAW Image Quality
We've recently started looking at RAW files converted with dcraw, an excellent freeware raw converter. dcraw usually offers timely support for the latest cameras, but more importantly, it does not apply any noise-reduction, sharpening or other corrections such as geometric distortion correction to the output files. (We found that Adobe Camera Raw still applies some limited noise-reduction when its NR settings are set to zero, and it also applies other corrections depending on the make and model of the camera). There will always be differences between RAW converters, in terms of the sort of de-mosaicing algorithms they use (the processes by which they convert the separate Red, Green, and Blue data sets to an array of full-color RGB pixels), but dcraw seems to use a fairly generic algorithm that delivers good sharpness with relatively few artifacts, and can be counted on to not apply any noise reduction if you don't want it to. (That said, looking at the ISO 25,600 and higher examples below, it's clear that dcraw's de-mosaicing approach does have some tendency to produce rectilinear artifacts in response to high noise levels.)
Below are crops from Nikon D3S RAW files compared to RAW files from pro grade digital SLRs, converted with dcraw.
Looking at the crops above, it's clear that the Nikon D3S is the new high ISO champ. The D3S does slightly better than the D3 at ISOs up to 6,400, then it pulls ahead of its predecessor significantly at ISOs 12,800 and above. The Nikon D3X and Canon 1D Mark IV do not perform as well in terms of noise, which is no surprise since they have a pixel pitch 5.9µm and 5.7µm respectively, while the D3 and D3S feature a 8.5µm pixel pitch. With only about 15% higher linear resolution, resampling the Mark IV's slightly larger 16-megapixel images down to the D3S's 12-megapixels won't come close to making up for the difference in high ISO performance. The Nikon D3S clearly outclasses the Canon 1D Mark IV in this respect.