[Bassnut (Fred)]

I understand the ISO selection on a DSLR simply selects amplifier gain. From the results ive seen, I cant see any reason to not use the highest ISO available (on the 300, 350 and 400D say, 1600iso) except for short exposures on high brightness objects eg M42 to layer on deeper exposures to stop core blowout. Deep space exposures always require streching anyway, so why add noise streching lower ISO settings when higher ISOs need less of that with higher gain cam settings?.

From the pics at 1600ISO ive seen, the extra streching at a lower ISOs just adds more noise.