Thanks for the link... very interesting!
I guess this explains why my dark frames don't work quite as well as I'd expect them to (even when manually subtracting layers in Photoshop)!
It's interesting that Craig comes to the conclusion that ISO 400 is the "best" setting to use on his camera, (primarily) on the basis of the potential dynamic range.
While a 12 min @ ISO 400 exposure theoretically has better dynamic range and more detail than a 3 min @ ISO 1600 sub, I've found two other equally important factors
during recent shooting:
1. Blooming. When exposed for the skyglow/nebulosity, I see blooming from the bright stars even at ISO 1600. At ISO 400 with the equivalent exposure value, they become huge ugly blobs - and often they seem to bloom more in one colour channel (e.g. red) than others, making them big weirdly-coloured bright blobs.
2. Noise and hot pixels. Shooting 12 min subs back-to-back on my Canon 5DmkII (even with ambient temps close to 0 deg C) has a huge amount of noise and hot pixels compared to 3 min subs. This noise reduces the effective dynamic range on the bottom end (and creates lots of black dots where the hot pixels are located).
I'm not looking forward to summer!