I have an odd theooy/question to propose. What if the "ISO1600" is the actual native resolution/sensitivity of the sensor and they are artificially tweaking and boosting the gain to simulate lower ISO?
Your theories are getting more and more exotic. If the base ISO were 1600, then ISO 100 would cause burning out the top FOUR stops.
Think what is happening at ISOs lower than the base ISO: plain overexposure; for example the A900 overexposes by 2/3 EV at ISO 100, indicating that the native ISO is around 160.
They did not have to "finally confirm" about the NR in the A700. Sony had freely published that they were doing NR on RAW, when they released the A700
That's right. I looked it up; the issue was, that there was no "off" setting.
One curious factor in the Canon 5DII, is that Canon swiftly came out with a firmware fix, that masked the "black dot" phenomenon (not present at all in the 21MP FF sensor in the 1DSMKIII). Is that not a clear indication that the RAW in the Canon is very well cooked and that the "black dot" masking, was again a further cooking of the RAW ? Any thoughts on that ?
The questions are justified, even though this has nothing to do with the actions of the A900.
1. The black dots have been caused by "stray" pixels. This needs an explanation.
Canon's CR2 (and at least one Olympus) creates a raw file containing the pixel values with an offset. This means, that a "black" pixel has the value around
128, 256, 512 or 1024, depending on the model. One theory is, that the A/D increases the voltage by a certain fixed amount, in order to catch irate values (negative charges) as well. Probably the other CMOS sensors are doing the same, but are not passing on the data. (The Nikon D300 is a notable exception.)
In this setting there can be and are pixels far under the "black level"; they will be changed to zero by the raw processing. This is happening all the time; there are a few hundred such pixels in the very dark areas
, usually with high ISO.
What was happening with the 5D2? Someone made a test shot directly before and after loading the new firmware version; these shots demonstrate the source of the black dots and the solution. Anyway, the cause of the black dots were very stray pixels: even with value 0 at the average black level of 1024, i.e. those pixel values represented -1024; they occured always directly at the right end of saturated pixels. These stray pixel values were overall in the negative range but concentrated at -1024, which indicates that they would be even lower but could not be represented.
This looked pretty much like overflow caused by sensor bleeding. I guess this is a limitation of the hardware; other sensors (like the D3/D700) create different phenomena caused by bleeding.
Now, back to the issue: the new firmware "puts these pixels into their context", probably by looking further to the right and using those pixel values. This is clearly "cooking" of the raw data; the same can be achieved in raw processing (and is done in DPP). I do not see any likeness to the noise reduction on raw data; I don't have any problem with *this* cooking (the problem is somewhere else: where the stray pixels arize). However, there *is* some other cooking in the 5D2 files, which I can not explain.
Looking at the file differences between a 5D MKII and a 1DS MK3 it does appear that the 5D MK2 is cooking more into the RAW
I am interested to see, how you came to this result.