HELP! Olympus E-PL1 Auto Iso vs. manual Iso

[ronyzmbow]

I am still new to my Olympus E-PL1 - so bare with me...
The default of Olympus E-PL1 Auto Iso starts with 200 Iso - the manual starts with 100 Iso. I can recall that some say the 200 Iso has a better Dynamic Range.
I have tried to compare the two option outdoors in a clear bright sunny day, and it seems as the 200 Iso images are more grainy and "dirty" look over all the image, mainly in darker areas of the image, while the 100 Iso images and cleaner. Other than this I did not notice any differences.
Any idea why and comments?

[mige0]

as far as I know, base ISO of the E-PL1 is somewhere at ISO 160.

So - anytime you are above base ISO, noise does increase (in the mentioned case its the increase for noise from 160 to 200 ISO).

If there is a ISO setting implemented below base ISO for whatever reasons (as is the case with the E-PL1) this can only be done by a trick that cuts DR but IMO does not improve noise. The latter I'm not 100% sure I have to admit (regarding no noise improvement beyond base ISO) haven't exhaustively tested myself