At the risk of taking this slightly off topic, Although I normally use Av mode to control DOF and use a lens's sweet spot, I also use +ve EC these days to minimise noise by shifting the histogram to the right, I think it's now known in some circles as the "Mosley Method" - (exposing to the right).
However I have recently been experimenting with ISO settings, until recently I have been using the lowest ISO available, wherever possible shooting at ISO 100 on my 30D believing this to give the lowest noise for a given exposure.
It was recently explained to me that on the 30D ISO 100 & 6400 are only accessible by activating the ISO expansion mode and are not in fact values recognised by the camera but are interpolated values, therefore the lowest noise setting on the 30D is in fact ISO200 in most cases for RAW shots and ISO 160 for JPEG (I still don't understand why there is a difference here). It was also advised that I should try not to use the other intermediate (interpolated values) and stick to 200,400.800&1600. as in low light conditions interpolated values will add noise. Basically the advice was to stay away from any interpolated ISO settings.
After using ISO200 for some weeks now I feel that shadow noise is lower at ISO 200 than 100 and this advice seems to work for me on the 30D. I would be very interested to hear of anyone else's experiences.
Just to get this back on topic - Av mode it is for me then!
Cheers, Peter.
Oh Lord, please help me to be the person that my dog thinks I am.