Contrast is not as good, though can be adjusted though post process. Sharpness wise, may be comparable to tele zoom, but lose out to tele prime lenses. Because of f/6.3-8, it's dark through viewfinder, so only limited to good day light shooting.
mirror lens is smaller in size also (compare with actual lens), easy for carry and transport.
To me, the chance for bringing out a mirror lens is still way higher than long tele lens due to it portability :sweat:
It all boils down to money talk?
If you afford a 500mm F4 or 600mm F4.5 prime lens than the mirror lens sucks!
If you have cash constrain (like me) then the mirror lens is :thumbsup:
One thing for sure, you cannot compare mirror with prime! The cash outlay is world apart too. Mirror can be sharp (max 8R prints) any bigger you need prime.
Do a search in CS cos there's some pics taken by this Kenko Mirror.
Enjoy you search...........dun end up like me with 3 mirrors, kenna the BBB mirror virus.
Oh! It's manual unless you are using sony or minolta cos they have AF mirror but very X