I borrowed a Catadioptric lens from the stores at college today, after one of our lecturers mentioned it earlier in the week. They're weird things. I might be doing the physics of this a diservice, but basically it has some sort of convex mirror arrangement, which bounces light and multiplies the focal length of the lens, so despite it being 500mm its much more compact that a telephoto lens. The main effect of the Cat lens is that it produces circular bokeh halos or "Iris blur".
I wandered about and gave the lens a bit of a testing this afternoon. Very heavy to hold steady, easier with a tripod. The smaller sensor on my D90 crops quite a lot of the shot out, so I'd get better results with a full frame.
None the less, its a lot of fun. The much increased focal length made surreptitious street photography less confrontational. I think I might try and take it down the coast over the weekend. Apparently water reflections can work really well with Cat lenses.
Some extra test shots.
- Nikon D90