In article <323E6A14.20DE2219@cornell.edu>, gsp4@cornell.edu says...

>I've been contemplating getting compact mirror lens around 500-600mm or
>so for EOS mount, and was wondering a few things about them.
>
>I know their quality is pretty bad compared to a non-mirror lens, but
>just how terrible is it?

Actually, it can be nearly as good as a first-rate long tele, and they
are (potentially) essentially APO's, even into the infrared area.

>What brands are better than others?

Nikon (older version of the 500mm f8), Nikon 500mm (current, is OK),
Minolta (and Minolta "Leitz") mirrors, and maybe a few others - though
the cheap ones I have tried varied from really terrible to passable
in a pinch (Tamron 500).

>Are any of them capable of auto-focus at all?

Minolta 500mm.

>Can they be reliably used with a teleconverter to make them even longer?

The older Nikkor 500mm is excellent on the TC14/14B converter, giving
a really sharp, tiny (relatively speaking!) 700mm (S L O W, though...),
but I would hesitate to use converters with any other mirrors.

>On that note, what's the best brand of teleconverter I should try? Do
>they interfere with the AE, and TTL metering?

Can't tell you much about, uh, canon... ;-), ;-), ;-), though with Nikon,
about +1/2 stop compensation is needed to meter TTL correctly with or
without converters, and AE, should one want to use it.... (here may be
its most useful application, since the mirror has no diaphram, and AE can provide a continuously variable shutter speed), works fine with mirrors
and converters on Nikons.
Hope This Helps