<< > I would say generally that mirrors are never quite going to perform like > regular lenses, however if you can provide a stable platform that will help > considerably. You know, I've seen this opinion expressed many times. It's a very common opinion within photographic circles. I've even fallen under its spell, though I have no experience with "mirror" lenses. >>
Doug. In my experience they seem to lack contrast. Also I think folks with less photographic experience than those here might be tempted to use the lens hand held - given the low weight that is a likely possibility. Then there's the cumulative effect of hand holding a lens of (relatively) limited aperture. I have used the Canon 500mm F8 (FD), Nikon 2000mm F11, Sigma 600mm F8, Tamron 350 and 500mm SP lenses. The nice thing about the Tamrons is (somebody else made this point) the great close focus. Kind regards Peter