Great post, Chuck. Thanks for covering the "tweener" (1/3-stop) ISO settings. (FWIW, there are no 1/2 stop ISO settings.)

Quote Originally Posted by Chuck Lee
I would say it is safe to say to use higher ISO and slightly over expose rather than under expose and push inpost.
Agreed.

Quote Originally Posted by Chuck Lee
I'm wondering if anyone can confirm this for the 50D?
I confirm it.

By the way, Chuck, you might be interested to see the chart of dynamic range over ISO settings, made by John Sheehy:

http://forums.dpreview.com/forums/re...ssage=31378147

Quote Originally Posted by Chuck Lee
The 5D is straight up! I hope the 5D MII is as perfect.
[iND, you can probably ignore the discussion between Chuck and I -- we like to get technical with eachother.]

The read noise ("high ISO noise") is improved greatly in the 5D2, but it still has pattern noise. Canon changed the way tweener ISO are handled in the 5D2. Now they are 30D-style "digital" tweeners instead of analog tweeners like the 5D Mark 1 and 1D series. That's actually a good thing, because the analog tweeners on the 1D series and 5D1 are implemented by a separate gain amplifier that adds enough of its own noise to make it just as noisy as pushing a lower ISO. So to avoid 1/3 stop of clipped highlights, it's better to avoid the tweener ISO on those cameras. (Actually, there is slightly less noise under ISO 400 using the analog tweeners, but often the loss in highlight headroom is not nearly worth it.)