The D6 has almost the same sensor, if exactly the same sensor as the D5. I have followed Thom Hogan's suggestions from his D5 e-Book. As D6 advice is still scarce, I strongly suggest buying his ebook:
I hope quoting key advice here on pp 366-367 does not break rules .... [and note some of this relates specifically to shooting jpgs). This advice follows from the detailed justification / lessons he draws of sensor performance at intermediate ISOs in the zone 100 to 800 with respect to minimizing noise :
"Here’s my suggestion for a completely acceptable use of the
automatic ISO option on the D5:
• Set High ISO NR to Low.
• Set Maximum sensitivity to 800. Only use higher values if you’ve
ascertained that they are acceptable to you, or if you are
shooting an Image size of Medium or Small.
• Set Minimum shutter speed to the lowest value you believe you
can handhold, or set Auto tuned to your usage.
• Avoid the JPEG normal, JPEG basic, and certainly the non ★
settings.
• Avoid using the flash. If you must use the flash, strongly
consider getting out of Auto ISO sensitivity control and setting the
ISO manually to avoid the micromanaging the automatic
system tries to apply."
"ISO Operating Suggestions
To optimize image quality, follow these guidelines for setting ISO
values on the D5:
• Set the camera to ISO 800 normally (or Auto ISO set to
800). The D5 is basically state-of-the-art when using its base
ISO level. No, setting lower ISO values doesn’t tend to net
you any gain in dynamic range. There are some small gains
at some intermediary ISO values, but they’re too small to try
to micromanage.
• Don’t worry too much about pushing out to ISO 2500. The
net loss of dynamic range from ISO 100 to ISO 2500 is only
a little over a stop. The D5 is most certainly not acting
ISOless up until about ISO 3200. It’s only at ISO 3200 you
start seeing a clear, and almost full stop, loss of dynamic
range with each doubling of ISO.
• Expose to the right. Underexposure generates additional
noise when you post process an image to restore brightness,
even with the great shadow detail on the D5. Keep your
exposure histogram pushed towards the highlights (but don’t
blow out highlights or any channel’s highlights by going too
far and pushing it off the right edge). Indeed, the minimum
amount of noise for a low contrast, gray target would be
generated by overexposing the gray target so that the
histogram spike was well right of center, then using Capture
NX-D or Photoshop to re-center the exposure (Curves,
Gamma, Exposure Compensation, etc.). Again, note that the
NEF (raw) files tend to be slightly underexposed by the D5. I
often add in some positive exposure compensation when
shooting raw-only.
• ISO 6400 is still extremely usable on the D5 and shouldn’t
be avoided. Note that camera dynamic range is lowered
enough to be something you need to consider, though. Also,
consider lowering your sharpening value in the Picture
Control you use slightly in order to further minimize noise
production.
• Don’t be afraid to use ISO 12800 if the situation warrants it.
Expect a slight loss of color saturation and some visible noise
at the pixel level as you boost ISO. Dynamic range is
significantly reduced from the base ISO value. Seriously
consider using a High ISO NR value of Low and slightly lower
sharpening in the Picture Control you use in order to totally
minimize noise production, plus avoid all high JPEG
compression settings.
• ISO 25600 and higher warrants close examination before
you commit to them....."
