I wouldn't put too much hope in that. The blackframe read noise of a mkIII 14-bit RAW at ISO 100 is 4.88 ADU. Translated to 12-bit, that's 1.22, a modest gain over the ~1.26 of the mkII (and perhaps just a camera-specific thing; the gain could vary a little from copy to copy). The mkII data goes up to about 3711 on the clipped specimens I've seen, and the blackpoint is 128, so there are about 3583 12-bit levels. The mkIII RAWs I have clip at about 15280 and have a blackpoint of 1024, so they have about 14,256 14-bit levels, or about 3,564 12-bit levels. Since ISO 100 doesn't even use close to full well, it should be linear right up to clipping, with no hidden extra highlights.
I notice that the comparison shots at Imaging Resource, [a href=\"http://www.imaging-resource.com/PRODS/E1DMK3/E1DMK3A5.HTM]http://www.imaging-resource.com/PRODS/E1DMK3/E1DMK3A5.HTM[/url] , show the the 1D3 at ISO 6400 as having virtually the same performance as the 1D2 at ISO 3200. With both cameras at ISO 3200, the 1D3 seems noticeably cleaner. With both cameras at ISO 1600, the differences seem reduced but the 1D3 still marginally better. I imagine if we could see comparisons right down the ISO scale to ISO 100, the differences would gradually reduce to the point where at ISO 100 there would be no noticeable difference except marginally greater resolution on the line charts.
If this is so, it confirms my impression that the DR improvements are directed at high ISO performance only.
Nevertheless, it looks as though Canon have provided a real
ISO 3200 in this camera, which is better than using the same exposure at ISO 1600.
Also, I'm wondering what the implications of the 10 frames per second speed might be for hand-held bracketed shots. Clearly, there has to be a minimum shutter speed for this, but I don't recall seeing it mentioned. For example, 10 exposures at 1/20th sec would take up 1/2 a sec, allowing a maximum time of just 1/20th sec to reset the sensor for the next exposure.
I wonder if it would be possible to bracket exposures at high ISO, using IS, and get shots for blending which are effectively as good as tripod shots?