Just a side note, the lowest ISO isn't always the cleanest noise wise, the best is usually the base ISO, on my 5D the lowest noise is at ISO 100, ISO 50 is an expansion it's shooting at ISO 100 then dialing exposure minus one.
FWIW on my 30D I used extensively the best noise performance was at ISO 160, although it had ISO 100 and 130
I hear that about Cannons. I'm a nikon guy, and its simply the lowest noise I've ever seen! It reminds me of the medium format from school, but the colour noise is even better than the older ccd on the medium format!.. I'll post a sample when I get a minute.
I was reading a bit and I guess you get 2/3 more light squeezed into the base 64ISO vs ISO100, so you get a much cleaner image vs100 on D810 and D850. I haven't really compared at ISO100 so I don't know how they look yet. I guess thats why they looked so clean!
"One of the D810's most significant features was its ability to shoot at ISO 64. There are two main factors that influence the Raw (saturation-based) ISO rating: efficiency and full-well capacity. Higher efficiency (a higher proportion of photons being registered) would push base ISO upwards, while an increased full-well capacity (capacity for electronic charge) pushes it down.
The D810 offered a lower ISO by increasing its full well capacity (or, at least, finding a way to squeeze a bit more out of it). This meant it was able to capture just as much of the light it was exposed to as the D800 but could tolerate more light before it started to clip. This meant it could be given greater exposure, which improves the signal-to-noise ratio and gives cleaner tones across the image: an improvement often interpreted as improved tonality.
This ability to tolerate an extra 2/3EV exposure is why we say that the D810 is able to compete with the latest batch of medium format cameras, whose 44 x 33mm sensors would capture 2/3EV more light at the same F-number and shutter speed."