I think it is not necessary always done digitally. It just shows that camera is being operated out of the optimal ISO range, so something most likely is being sacrificed.
At high ISO's this might just be the level of reasonable quality, where extended mode clearly states that the camera is being pushed over its limits and you shouldn't expect anything good.
Maybe normal iso is just the range at which metering produces most useful results and you wont get weird Av/Tv combinations, like 1/2000@F4 in daylight.
Instead of increasing signal amplification, you could, for example decrease the reference level of ADC (analogue value which equals full digital range, like 1V=1024 or 0.5V=1024). In such case much lover analogue value per bit had to be converted, taking greater impact from conversion circuitry.
At the low site it could be not so good reference level. Because if you can get stable and clean 3V from 6V battery, you may not have enough headroom to get stable 5V reference if card writes, flash charges can AF current gulps can cause battery voltage drops to 4 volts.
Most likely the programmable amplifier has free enough choice of amplification, but again when inputting extreme values you may not know exactly when it's hitting power supply limitations or getting non-linear.
So with this i'm saying that this may not always be a digitally pushed mode, there are many other options that can be used and get out of their qualitative ranges.You cannot tell it for sure unless you do a qualitative, controlled test with a
pre-bayer,pre-dark RAW file.
Last edited by ytterbium; 09-30-2009 at 03:01 AM.