To compare noise levels under real-life conditions we shot this scene using the Canon 400D / XTi, Nikon D80 and Sony A100 at each ISO setting. The Nikon's High ISO Noise Reduction was set to Standard. The D80 again metered a brighter exposure, but for consistency here, compensation was applied.

Each camera was fitted with their respective kit lenses: the Canon EF-S 18-55mm, Nikkor DX 18-70mm and Sony DT 18-70mm. These were adjusted to deliver the same field of view and set to f11 in order to accommodate the high ISOs under bright conditions.

The image above was taken with the Nikon D80 at 27mm f11, with a sensitivity of 100 ISO; the original JPEG measured 4.23MB; the Canon 400D / XTi and Sony A100 images were taken with the same exposures and their 100 ISO samples measured 3.77 and 3.11MB respectively. The crops are taken from an area just below and to the left of the centre.

Starting with the lowest ISOs, the Nikon D80 clearly delivers the most detail in the crops below, although as explained on our first results page, the Canon is let down by its kit lens. Quality remains good through to 400 ISO, although at 800 ISO and above, greater differences emerge.

At high ISOs the Sony A100's noise levels become the highest in the group, while detail in turn becomes noticeably reduced. The Canon crops also appear increasingly noisy compared to the Nikon, although closer examination of these and other samples reveal a different noise reduction strategy. At high ISOs, the 400D / XTi sacrifices noise levels (especially chroma noise) for retained detail, whereas the D80 tends to smoothes out noise for cleaner results, but sometimes at the cost of a little smearing.

Which approach is preferable is entirely personal, although one thing's for certain: the Canon 400D / XTi and Nikon D80 perform better at high ISOs than the Sony A100.