(...) He uses the engineering definition of DR (dynamic range = raw saturation level divided by read noise). At base ISO both cameras have a DR of about 11.3 stops, and gain about 1/3 of a stop when going from 12 bit to 14 bit mode. It would appear that 12 bits would be sufficient for these cameras.
Bill, it's nice to check in objective figures what one suspected.
Moreover, I would say that this DR figure in terms of Sat_Level/Read_Noise (11.7 f-stops) is too optimistic when compared to what it's usable in real photography.
I shot a high dynamic range scene with my Canon EOS 350D at ISO100 to make a subjective but valuable calculation of the DR:
The histogram shows the scene contained information along around 12 f-stops.
I developed it linear and plotted its distribution in f-stops:
Looking at the texture detail in each f-stop:
Beyond f-stop -7EV there is nothing but noise grain. We can conclude that 8 f-stops
(0EV to -7EV) of usable dynamic range would be already quite optimistic for this camera. By repeating this test on the new 14-bit Mark III I don't think at all that bit depth will reveal as being determinant in defining the new achievable dynamic range; IMO still noise will set the low end of the DR
and probably the influence of the 2 extra bits will be almost negligible for DR. Allowing 1 f-stop or 1.5 f-stops of improvement in noise for the new sensors (which is not a joke), we would estimate the final USABLE DR in around 9 or 9.5 f-stops, still recordable using a 12-bit linear A/D. The improvement would thus be thanks to noise optimisation, not to higher bit depth.
Panopeeper, bit depth doesn't guarantee achievable DR, but sets a physical limit to it if linear RAW encoding is used (and this is the case of most sensors, not Leica's M8 for instance). To have N bits of bit depth is not a sufficient condition, but a necessary condition to capture N f-stops of DR. And that assuming that the lower f-stops would be poorly represented, so actually you will need more than N bits for properly recording N f-stops of DR (remember we are talking about capture, not about image post process encoding).
A 12-bit RAW has the following levels for each f-stop:
0EV: 2048 levels, 2048..4095
-1EV: 1024 levels, 1024..2047
-2EV: 512 levels, 512..1023
-3EV: 256 levels, 256..511
-4EV: 128 levels, 128..255
-5EV: 64 levels, 64..127
-6EV: 32 levels, 32..63
-7EV: 16 levels, 16..31
-8EV: 8 levels, 8..15
-9EV: 4 levels, 4..7
-10EV: 2 levels, 2..3
-11EV: 1 level, 1
As you can see, the lowest f-stops have a strong lack of tonal variety. There is a direct link between a maximum achievable DR and the minimum number of bits required for it.