"PeterN" wrote in message
...
There is also a practical limit in noise level at a higher ISO. My D200 ws
quite noisy above 800. My D300 produced usable images at 1600-2000,
although there was some noise. Though with today's noise reduction
software, my guess is that the limits may be higher.

And many new cameras allow you to set the max ISO used by auto ISO, so you
can simply choose at what point you think noise is excessive for the camera
being used, and not go there.

Trevor.