For a while I used a Tamron SP 8/500. It is compact, lightweight and easy to use from a tripod (which I use anyhow). Compared to the huge Novoflex follow-focus telephoto lenses and all those nice modern expensive telephoto lenses that are even bigger and heavier this small gadget is a pleasure to carry, and for what I do it's a great concept... and I admit that I like the look:
The Tamron has a reputation to be a better-than-average mirror lens. But though it has a built-in hood it does not like backlighting situations... and I love backlighting. I can take shots like these with an old 4.5/80-200 Nikkor-C hands down, but with the Tamron I could only see 24 x 36 mm of glare in the viewfinder:
(All made with Nikon F2, Kodak Ektar 100, scanned from 1-hour-lab prints)
Reflex Nikkors might be better... and most probably they are better than all those el-cheapo mirror lenses on ebay.
There were several versions of the 500mm Reflex Nikkor. The last version is still pretty expensive. Is it worth the extra money compared to its ancestors? Is anyone here who can share some experience with the various versions? How are these lenses in backlighting situations?