In article <4nifns$i9m@freenet-news.carleton.ca>, ak926@FreeNet.Carleton.CA says... [....]

>Regarding the advantages or otherwise of using a 2X on a good >telephoto: in my experience, it depends on the quality of the doubler. >I did some tests a year or so ago, photographing the classified ads >from the local newspaper, filling the frame top to bottom, with a
>Nikon AF 180 with and without a) a Tamron 2X 7-element doubler and
>b) with a Nikon TC201, on Delta 100 film.
[rest of long, excellent post deleted for space reasons, alas....]

Wow! Nice post! I appreciate it when people take the time to actually
try something (instead of just quoting material someone else has
written, or expressing an unfounded opinion...), and then present the results. I would note that: Lens performance can change radically with focused distance (something often overlooked when chart-testing), and close-focus performance at wider apertures is often relatively poor in otherwise excellent lenses (the 180 AF, 85mm f1.8 AF, and 85mm f1.4 MF Nikkors [and the macros] are unusually free of this problem among the short/medium Nikkor teles); I have found the Vivitar 2X Macro
Converter to be the approximate optical equal of the Nikkor TC201;
I was not very impressed with the Tamron 500mm mirror either, but
the older-style Nikkor f8 mirror is excellent (except near closest
focus distance).
Hope This Helps