Well, the Nikkor TC20E (designed for the AF I/S Nikkors [only])
arrived today, and since I finally found one at a good enough price
to take a screw driver to it to remove the front bayonette so that
I could file off a small tab that prevents the mounting of anything
but those big and horribly-expensive EDIF-AF-I/S Nikkors with the
built-in focus motors, I can now report a bit of preliminary findings
(having just processed and glanced at the second roll of film shot
with it on a few lenses...;-). (Whew! I trust you didn't get as lost
reading that as I did writing it!;-) With the small tab removed,
the relatively compact (compared with the TC300/1), but surprisingly
heavy (3/4 pound) TC20E will fit a few lenses the TC300/1 won't, plus
the usual ones 300mm and over that it will. On the AIS 135mm f2.8,
performance was not very good (the TC200/1 would be better).
On the 80-200mm f2.8 AF, it was fairly good at the short end of
the zoom range by f4, and quite good by f5.6. At the long end, it
was OK at f4, and fairly good by f5.6. This converter works better
on the 80-200mm f2.8 than the TC200/1 does, though it is not ideal
(and not as good as the performance of the TC14C on this lens).
It is also very hard to focus the 80-200 with the TC20E installed.
The TC20E was disappointing on the 300mm f4 AF - the 100-500mm Cosina
zoom on its own easily beat this combination (though it is only 500mm
instead of 600mm). With it on the older 500mm f8 mirror, conditions
may not have been good enough to see the limits of this combination,
but results were not high-quality. I did not have time to try the
converter in a macro set-up, where I often use converters for increasing
magnification. Preliminary conclusion: this converter probably ought
to be left for use on the lenses it was designed for, though it
does provide decent performance (better than other 2X converters)
on the 80-200mm f2.8 AF Nikkor, and it MAY be good for use with long
extension tubes on the front when doing high-magnification macro work.
Hope This Helps
(web page coming soon, if all goes well - under the name David Ruether;-)