So my D90 offers "High-ISO Noise Reduction". Sounds like a good thing, but obviously there must be a cost of some kind. The settings are "Off", "Low", "Normal", and "High", and the default is "Normal".
What are the pros and cons of using this feature? Why not always set it to "High"? Or, should I be turning it off?
The pro's are self-evident:
The biggest con:
The high-iso noise reduction might remove detail mistakenly. While newer camera algorithms have gotten better at it, it's still not fool proof.
The settings between Off, Low, Normal and High dictate the amount of tolerance used for the setting, which affects the amount of detail that might be lost.
In general I wouldn't recommend doing anything in camera that is irreversibly "baked" into the image, as such things can always be done better, with more control, and more importantly the option to undo, in post on your PC.
There is another feature called Long Exposure Noise reduction which shoots a black frame (i.e. one in which the shutter is closed) in order to remove "hot pixels" and other artefacts which show up on long exposures. This feature is useful and can't be replicated in post, unless you shoot your own black frames (with the lens cap on and viewfinder covered).
Like many in-camera features, this boils down to how much do you trust your camera manufacturer vs. how much do you think you can do better yourself by doing it manually in post-production.
As others have noted, once you do something in-camera, you often can't undo it in post. With noise reduction, you'll be losing image detail just like you would when applying noise reduction via Lightroom, Noise Ninja, or other software. The difference is that when you do it yourself, you have more control.
