I owned a 500mm Nikkor Cat a number of years back and found the lens far too soft for my liking (I ended up giving the lens away); my other telephoto Nikkors (300, 400 and 600mm) are IF-ED glass so maybe my basis of comparison is unfair. That said, I did find the "donut effect" interesting, but not something I would use on a regular basis. From time to time, however, I have been tempted to give a try out to the 500mm Nikkor Cat ("New") to see if any improvement is evident in the last release of the design...