Sharpening (CSM 23)
Through custom setting 23 you can select from four levels of sharpening: None, Low, Normal and High.
|CSM 23-0: Normal|
|CSM 23-1: Low|
|CSM 23-2: High|
|CSM 23-3: None|
At anything above Low the sharpening algorithm has a tendency to introduce sharpening artifacts such as joined pixels, speckle artifacts and white halos around black lines. I steered clear of using too much sharpening by setting CSM 23 to 1 (Low) and (if necessary) sharpened the images later in Photoshop (even this isn't necessary if you shooting for resolutions lower than native - for the web for instance), this procedure produced a far cleaner image.
Tone (CSM 24)
Through custom setting 24 you can select one of 5 custom tone curves: Auto, Normal, Contrast -, Contrast + and Custom. Custom curves can only be programmed through the Nikon Capture application. Each of these settings applies a different "correction curve" to the RAW data before it's turned into a JPEG / TIFF. (In RAW mode the Tone is recorded in the header of the RAW file but image data is not modified).
Majority of pixels level 11 - 229
|CSM 24-0: Auto|
Majority of pixels level 5 - 229
|CSM 24-1: Normal|
Majority of pixels level 5 - 203
|CSM 24-2: Contrast -|
Majority of pixels level 5 - 235
|CSM 24-3: Contrast +|
Generally speaking the Auto setting produced the best results, with the camera selectively choosing (this is an assumption base on observation) either Normal or Contrast - curves. Contrast - is useful if you're going to be post-processing the images as it produces the "flattest" image without clipping the low or high end of the grayscale.