Nikon D5 High ISO NR
Nikon D5 High ISO Noise Reduction
The Nikon D5 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 D5 manual doesn't say at what ISO High ISO Noise Reduction begins to be applied, so we've included crops from ISO 50 on up here.
See for yourself how the Normal and Off settings work compared to RAW files with no noise reduction (or sharpening) applied. Click on any of the crops below to see the corresponding full-sized image.
High ISO noise reduction seems to kick in already at ISO 200, however it is quite subtle until ISO 800, where it starts to impact fine detail in our difficult red-leaf swatch. And as is usually the case, the Off setting is not truly off, at least at sensitivities above base ISO. At intermediate to high ISOs, we would probably elect to shoot with the Low or even the Off setting, to better preserve fine detail. As you can see, sensitivities above the maximum native ISO of 102,400 or perhaps extended ISO 204,800 are so swamped with noise we wonder why Nikon even included them, other than for pure specmanship.