Barry_Green
Moderator
But, be aware that there is no given standard for noise level at base ISO, so -- you can't really directly compare them. If one manufacturer's tolerance for noise is higher than another's, then they might "rate" their camera faster, even though your particular tastes may be for less noise, so you may "prefer" the "slower" camera.
And, then again, there's the simple fact that not every manufacturer considers brightness equally. Look at the GH1 vs. 7D ISO discrepancy for example; many folks who have tested them have shown that the GH1 at 400 ISO is noticeably more sensitive than the 7D at 400 ISO, leading them to the conclusion that the GH1 is "faster" than its stated ISO, or that the 7D is slower than its stated ISO.
So actual ISO numbers should be taken as a ballpark and not much more than that.
And, then again, there's the simple fact that not every manufacturer considers brightness equally. Look at the GH1 vs. 7D ISO discrepancy for example; many folks who have tested them have shown that the GH1 at 400 ISO is noticeably more sensitive than the 7D at 400 ISO, leading them to the conclusion that the GH1 is "faster" than its stated ISO, or that the 7D is slower than its stated ISO.
So actual ISO numbers should be taken as a ballpark and not much more than that.