Quote:
Originally Posted by andyc
1: I've been trying to read quite a lot about ISO settings, and so far as I can work out: you don't gain any more at all in sensitivity beyond about ISO800-1600, possibly even less; but you lose 50% in dynamic range per ISO doubling; and background noise covers a bigger fraction of that dynamic range. I'm still not perfectly sure about the details, but you may be better off shooting at ISO 800/1600 rather than 1600/3200 and then stretching with 'curves' in Photoshop? Perhaps that would make it a little less noisy?
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This is an interesting comment and one I'd like to see explored and clarified a bit more because it differs from my own understanding, which may well be wrong.
My understanding is that dynamic range is basically the range that constitutes the "intelligible" part of the signal and by increasing the ISO, a large part of the dynamic range loss actually comes from the increased noise drowning out the signal making it "unintelligible". The remainder would be highlights that get lost due to clipping that wouldn't otherwise take place. So unless I'm mistaken, you don't lose out with decreased dynamic range
and increased noise, I think they're one and the same.
The flip side to that is that some cameras, (some?) Nikons at least, clip values within a certain range of 0, so by upping the ISO and pushing the signal outside of that range you'd actually be increasing your dynamic range.
I saw a really good article on this a while ago that explained it much better than I can, but I have no idea where it is now. It indicated that there's a certain sweet spot with dSLRs where you get the most dynamic range... ISO 400 was a good spot for one of the particular cameras.