Some small notes about Sony sensors that may affect the discussion. First, and importantly: They have a variety of hardware-level built-in noise reduction technology. Two key types, if I remember correctly, as well as a couple other features that improve their sensors. One to pretty much eliminate fixed pattern noise by accounting for differences in transistors at the hardware level. Another that uses an extra accumulator that measures dark current noise before computing the charge accumulated in the photodiode itself (CDS, or correlated double sampling). In addition to these explicit noise reduction technologies, Sony Exmor sensors also use column-parallel ADC. High frequency electronics have the potential to introduce more noise. Sony's CPADC, being hyperparallel, means each ADC has to do less work, and therefor does not need to operate as fast or on as many pixels as ADC's in Canon cameras. This also leads to lower noise. They use copper wiring which allows the CMOS to be thinner, along with a double layer of microlensing (which appear to be gapless) to direct more light into each well. Sony holds patents for all of these technologies, as well as for an approach to backlit sensor fabrication (which does not seem to be used in Exmor sensors, not sure why.)
For one, Canon does not seem to have patents on similar technology in most cases. They do offer some hardware-level noise reduction in line with Sony's CDS, or correlated double sampling, to eliminate dark current noise before reading the photodiode charge. Canon seems to use a different approach to fixed pattern noise however, whereby they set a non-zero pixel level floor, such as 1024 (or possibly in the case of the 5D III, 2048). This information seems to be derived from masked off pixel borders around the edge of the sensor, and can be used to adjust the black point of a CR2 RAW image at time of processing. The non-zero floor allows both positive and negative
adjustments to black level, depending on how much things like fixed pattern noise exhibit. However, at least based on information I've been able to find so far, this non-zero floor does not seem to "push" the maximum saturation value up at all. As far as I can tell, this leads to a fixed limitation on dynamic range since your eating into the maximum saturation level with a higher-than-zero black level...and may very well be the reason Canon sensors have been stuck below 12 stops of DR.
All that aside, Canon has made explicit
claims about improving
the dynamic range of their new sensors. From the Canon EU site (http://cpn.canon-europe.com/content/education/technical/inside_canon_eos_5d_mark_iii.do;
see under Image Quality, Processing & Playback):
Like the EOS-1D X’s sensor the full-frame CMOS sensor of the EOS 5D Mark III offers increased light sensitivity, image noise reduction at higher ISO speeds, and a wider dynamic range.
The above is from a caption. They also provide the below information:
CMOS sensors make use of microlenses to direct the light into each pixel well. Canon’s first full-frame sensor with a gap-less microlens design is found in the EOS-1D X and the sensor in the EOS 5D Mark III features the same technology for improved light gathering ability. Gap-less microlenses mean that no matter what angle the light arrives at the sensor from it is directed into a pixel well where it can be used most effectively. In essence it means that no light that gets to the sensor is wasted by not making it into a pixel.
Unless Canon truly does not have an issue getting caught in an outright lie (i.e. if their new sensors still don't achieve more DR than the 11.95 stops measured by DXO or 10.3 stops measured by DR), such a claim has to mean something
has been improved with 1D X and 5D III dynamic range. (Or at least, so one would hope...)