Check out this thread. A perfectly reasonable relay of information
from DXO about the differences in sensitivities of cameras. DXO is
probably the only site that deals properly with this clearly evident
issue. Dpreview tweaks the illumination levels on all its tests shots
when it does reviews, which explains why (despite real-world
experience being the opposite) all the shots appear the same from
camera to camera. I've owned a slew of different DSLRs and can state
that even with the same manual lens being used and the same manual
exposure, (thus eliminating t-stop arguments) different cameras render
different illumination levels in images, leading some to show even
more noise in shots than others when levels are equalized. Marked
ISOs are clearly not the same from camera to camera for raw shots.
P.S. Who cares about JPEGs? The camera manufacturer can create any
levels it wants for them so comparing them is insane, except to judge
artifact control.
http://forums.dpreview.com/forums/re...ssage=34086189