In article <46826c$sen@alphabits.shr.dec.com>, russo@viis6.viis.shr.dec.com says...
> I would like to hear comments from anyone who has used a
>mirror style lens. I seen a Nikon 500mm F8 mirror lens the other
>day and was intrigued.

A "good" mirror lens can be very good, almost the equal of the big, expensive ED lenses, if used with an awareness of their shortcomings.
(BTW, the older 500mm f8 Nikkor is excellent near infinity, and still
excellent when used with a TC14B converter). Mirror optical quality
is distance-sensitive, as it is with other types of lenses like speed
lenses, some zoom lenses, some teles and wides. Mirrors are physically
short and light, which makes them great for packing, but very difficult
to use (the mass x length of standard design long lenses helps in
getting sharp pictures). A gyro-stabilizer is particlarly useful when
hand-holding the short, light mirror lenses. High shutter speeds,
and/or a sturdy tripod (possibly weighed down - with SLR mirror up) are necessary otherwise. Mirrors have poor viewing images, and appear hard to focus, but I rarely miss-focus my mirrors - just have a little faith and go ahead and shoot 4-5 frames of everything (be aware that there is no diaphram to stop down to begin to cover focus errors). Generally, it is a good idea to rate the film speed about 1/3 to 1/2 stop slower
to compensate for the center "hot spot" (especially with center-weighted meters) that mirrors produce. Out-of-focus highlights are rendered as doughnuts - distressing to some people, not to me. The out-of-focus image can be very high in contrast, providing for the appearance of greater than expected DOF. (I once shot a couple of magazine articles
[and covers] on humorous building details [most of which were, of course, WAY up THERE!] using the older version 500mm f8 Nikkor, and all the photos appear sharp all over, even when shooting down the side of a building, or up at a sharp angle. [Most of the photos were taken hand-held with Tri-X, with the covers taken with Kodachrome 64 using a tripod.]) Mirrors are convenient to carry, less expensive than standard teles, APO (even into infrared) - bargain lenses, if you buy a good one.
Hope this helps.