Misha IMO b) 4 Seconds @ ISO 100 b) 4 Sec @ ISO 100 Because the ISO value has more impact that lenth of exposure. (unless its very long 30 sec or more) I have played with this a little, 800 ISO can be pretty noisy even with a fast shutter. Also noise shows up more in dark/uniform areas As Danob said it also depends on the type of sensor, and the CMOS seems to win out on this issue more than a CCD because of its lower power comsumption.

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