The whole CCD real iso range on MFD has been shrouded in some mystery over the years. Does a CCD really have a gain, i.e if you increase the iso, does it really increase the gain of the CCD, like on a CMOS chip. From what have been able to ascertain, is that no, basically a CCD is a one level iso chip, and any increases are just metadata increases. This changes on the IQ and P65+, with sensor plus I am not sure what the CCD gain increases to, but it has to be somewhere in the iso 400 range, as the files are notably cleaner than their full frame equivalents albeit at a loss of 3/4 of the total resolution of the chip.
I was surprised when the 50MP CMOS came in at a base of iso100, as I would still prefer 50 base.
As to the iso 50 real base vs 100, I really don't know the answer. I do "feel" from my shooting that at 50, with a IQ160 or 260, you do get a better performance in DR, especially in highlight recovery and a bit more in shadow recovery/noise. CCD shooting is much tighter than with CMOS in that you have so much less slop in iso recovery. You really have to be right on with the exposure, and the tech camera limitations due to Copal shutters doesn't help much. (One reason I had hoped to see the Arca FS come in at a bit more reasonable price point).
When I shoot in the field I often bracket iso ranges on my IQ260, 50, 100 and 200. There are sometimes that a shot will be best at 50, others 100 and even some at 200.
The data shared by Voidshatter is most interesting and I need to get out my DF and try a similar test. I don't have raw digger, but just working in C1 should show some interesting results.
Paul
