In Nikon parlance, long-exposure noise reduction off is called Mode 1, and on is called Mode 2.
Mode 3 is a trick for defeating the "star eater" (p. 17). It is not a menu setting. To use Mode 3, turn long-exposure noise reduction on, take the picture, and then, when the camera is taking the second exposure with the shutter closed, switch the camera off. At this point a "truly raw" image has already been stored on the memory card, and you are preventing the camera from replacing it with a processed image that shows fewer stars. Of course, no dark frame subtraction has been done either; you will have to take dark frames and subtract them later using your computer.
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