D3 NEF Files Can Be Affected by Noise Reduction
Prepared 2008-03-07 (147/53340) by Bill Claff

I had previously researched this for the D70 but never published those results.
Due to some renewed debate on the subject for the D300 and D3; I retested the D300 and D200 (see D300 and D200 NEF files can be affected by Noise Reduction) and received some D3 data from a collaborator.

The test procedure is quite simple.
He took a pair of "lens cap" shots at every shutter speed at ISO 200.
The expectation would be that the noise would be level or rise slightly with longer exposures due to Dark Current.
(FWIW, the test shots were taken in order of longest to shortest duration.)

However, there is an abrupt drop in the noise (and signal) at a particular shutter speed; 1/4s.

Here is a chart of the results showing noise (signal is quite similar):