In article , at491@FreeNet.Carleton.CA says... (...)

>Do mirrored lenses have other drawbacks besides fixed aperature?
>Will my slides be noticeably less sharp than a standard fixed
>focal length lens? Does a mirrored lens compress/flatten the
>image more?
>I am looking at a used Nikon 500 mm mirrored lens (f8) in a local
>camera store for $500 (Cdn). The same store also has a new Samyung
>500mm mirrored lens (f8) on sale for $168. I looked through each
>(mounted on two Nikormat bodies), and the Nikon was considerably
>sharper and crisper. It was also considerably wider, longer and
>heavier, but still a featherweight compared to a standard 500 mm
>lens).

Mirror lenses usually have a center "hot spot" which can mislead
camera meters (I set the ASA 1/3 stop low when using a mirror),
and they are difficult to focus in the field (though I usually hit
focus accurately - it just seems hard). Some people hate the
"doughnut effect" produced when shooting out-of-focus highlights.
Since the mirrors are slow (and often 1/3-1/2 stop slower than rating),
hand-holding is practical only with film speeds at or above 400 on
bright sunny days, alas - so slide shooting is difficult (I do have
a gyrostabilizer to sell that helps mightily with hand-holding
mirror teles....;-). I would recommend looking for the older, larger
and heavier Nikkor 500mm f8, since it is a bit sharper at some
distances than the newer one, would be cheaper, and it works well
with the TC14 and TC14B converters (if you can stand the SLOW speed).
Hope This Helps