To measure and compare noise levels we photographed the standard Gretag Macbeth ColorChecker with each camera at each of their ISO settings. The D80's High ISO Noise Reduction was set to Standard.

The crops are taken from the original images and presented here at 100%. To compare typical noise in skies and dark shadows the crops were taken from patches 3 and 24 respectively.

Tonal and colour differences aside, the Canon 400D / XTi and D80 perform very similarly up to 400 ISO, with both delivering noticeably cleaner results than the Sony A100. At 800 ISO and above though, greater differences become apparent with the Canon crops appearing noisier than the Nikon and the Sony crops looking noisiest of all.

At first glance it would therefore appear to be a winning result for the D80, followed by the 400D / XTi in second and the A100 trailing in third place. But it's important to remember the Gretag test chart only shows solid colours and often hides smearing or loss of detail through noise reduction systems.

When comparing real-life results on the following page and in our Gallery samples, the 400D / XTi and D80 exhibit quite different approaches to noise and noise reduction. The Canon appears to accept greater noise in order to retain detail, while the Nikon appears to apply greater noise reduction (especially to chroma noise which is virtually absent), although often at the cost of smearing ultimate detail.