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As the signal from the sensor is amplified, noise enters the picture. High ISO noise is not a differentiator when choosing between the T3i, T2i, 60D and 7D - I don't perceive any differences (other than that my T3i produces slightly brighter images). ISO 1600 and 3200 are the settings my tolerance for noise maxes out on. I reserve ISO 12800 for emergencies only.
The 5D II is obviously the winner in this competition.
The T3i's with-noise-reduction examples above have a range of noise reduction added - from 1,2 (Luminance,Chrominance) at ISO 100 up to 8,16 at ISO 12800. These examples clearly show that noise reduction reduces the visible noise - and reduces the fine details as well.
Here is another example that includes fine details.
Back to the Canon EOS Rebel T3i / 600D Review.
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