Images shot at ISO 100 are clean and free of noise.
At ISO 200 there's the merest hint of softening, but it's nothing to worry about.
By ISO 400 the softening has become much more noticeable.
By ISO 800 image quality has really started to unravel, with shadow areas reduced to a near blur.
Image quality at ISO 1600 really isn't all that great.
While ISO 3200 is best avoided at all costs.