I know that the ground glass is described as spinning, but isn't it, in actuality, moving back and forth on the same axis? Is anyone familiar enough with the mechanism to clear this up for me?

nope, the 300 series spins like a record, hence the vortex which is visible as you close the lense up... the 400 spins on an elliptical path eliminating that spot, although I assume it can create a big circle if you know where to look... haven't seen a 400 series yet.

The 400 spins in a elliptical manner. You can see it when the camera is detached. I have not seen any type of artifact on the image regardng the spinnng I will try to capture ground glass spinning on video and post latter this week as media file.

See: http://stevecahill.home.comcast.net/mini35/min35.htm

for informaton about Nkon lens on min35.

Regards
Steve