I was playing with the Nikkor f2.8 60mm Macro on the D700 body today and I noticed something strange. I'm sure some of you vets will know what's happening here. I was trying to set the lens to f2.8 when I noticed that it would stop me at f4.8 and not let me go larger. This confused me until I realized that if I turned the focus ring from where it was(closest focus) to infinity, the aperture then moved to f2.8. I rotated the focus ring completely both ways and realized that the camera was stopping down and up, based on the focal distance. Since when did primes do this?? I've used plenty of primes from all brands, a few of those were dedicated macros like this one, and I've never seen the aperture vary with the focal distance. Is this just a quirk of this particular lens or are there others I've net yet encountered?