Noob'ish question on Nikon ISO measurements

[ecnal]

Just a quick question - I'm looking at reviews/specs of the D90. Has an ISO range of 200-3200, but in parenthesis next to it it says "(100-6400 expanded)".

What does that mean, expanded? Looking for some clarification!

Thanks!

 

[TJ K]

Those are the high and lo settings. 3200 is the native iso but you can crank it up to 6400 but that will be horrible and unusable. Then you can go from normal iso of 200 and bring it down to iso 100 for even less noise and slower shutter speeds if you need it. They don't really intend for the 6400 also known on the d90 as Hi1. Hope that helped out.
tj