Let's compare,
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I shoot with D700 this time so can't exactly compare the ISO performance with the D3100.
But here's one taken last year with the D90.
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Similar condition as my friend's D3100, and the same lens.
Added on March 27, 2011, 1:16 pmWhen I saw 'bad', I'm referring to the noise. Look at the shadows, the noise is quite obvious there. If my memory serves me right, appears worse than my D90 :S. But been ages since I used my D90 so I don't really know haha!