Ron, It depends on the lens more than the camera. If your macro lens will focus at a 1:1 ratio without extension tubes, you obviously don't need it. My lens (55 f/3.5 Micro) focuses only to 1/2 half size, so I need the tube to get it to focus close enough to dupe the slide, which with a D700 will be essentially the same size as the sensor -- a 1:1 ratio. To get closer than 1:1 in order to crop the slide, I have to add the shorter PK 11 tube.
"One should photograph objects not only for what they are but for what else they are." -- Minor White