Nikon D800 High ISO Noise Reduction
The Nikon D800 offers four High ISO Noise Reduction settings: Off, Low, Normal (default), and High, allowing you quite a bit of flexibility in choosing how you want to make the trade-off between subject detail and noise levels in JPEGs. The Nikon D800 manual doesn't say at what ISO High ISO Noise Reduction begins to be applied, so we've included crops from ISO 50 up here. Note that the Nikon D800 manual does say when Off is selected, noise reduction is only performed at ISO 1,600 and higher, and the amount is less than Low.
See for yourself how the four noise reduction settings work. Click on any of the crops below to see the corresponding full-sized image.
The above crops show the effects of the 4 levels of high ISO noise reduction, under the HMI lighting we use to simulate standard daylight. As you can see, the High ISO Noise Reduction setting already has an effect at ISOs as low as 400. At higher ISOs, the trade-off between detail and noise can easily be seen.