What are the mechanical and optical differences between the two versions of the Noct. So far, I have read and am led to believe that the 7 blade is mechanically superior for the following reasons. - Ai body has a lens mount that is secured with 5 bolts instead of 3. - Aperture connecting lever is steal instead of aluminum. - Some weight savings changes were done that may affect durability. - Helical pitch of the focus mechanism is slower allowing for more fine tuned focusing. Optically, the 9 blade maybe superior: On the other hand, the 9 blade version might produce a slightly better bokeh stopped down because of a more circular opening of 9 blades. I don't know if there are any other improvements.