Mirror lenses, which are also known as ‘catdiotropic’ or ‘reflective,’ were all the rage in the ’70’s, and 80’s but dropped out of favour in the ’90’s . In the digital age do they have a purpose? This article tests several mirror lenses from different manufacturers, explains the advantages and disadvantages compared to conventional (refractive) lenses and shows how most of the disadvantages can be overcome in the digital darkroom. There are plenty of test pictures throughout and sample images taken in the years since I carried out the test all available in a Flickr album at up to full size.
Up until around 6 years ago, Tamron, Nikon, Zeiss and Minolta all still had mirror lenses in production. Now of the big brands only Sony have one available, and this is the previous Minolta model rebranded. There are some other cheaper makes such as Kenko, Vivitar and Centon new. There are plenty of lenses to choose from on ebay, and I bought 4 of them to evaluate, eventually selling all but one.
- 500mm f8 Mirror lenses from Nikon, Zeiss and Tamron
Articles about lenses and filters and tests.
Zeiss manual focus lenses for dslrs
Wayne Grundy's PhotoTech Blog 
this re very nice part of gadget, but can they work with canon cameras
Mirror lenses from all these makes in my test worked on my Canon EOS 5D mk2 with adapters I found on ebay.