You asked
How sharp is the olympus 9mm f 8 fisheye body cap lens?
I don't have a sharpness rating for the Olympus 9mm f/8 Fisheye Body Cap Lens, so I won't guess at one. What I can tell you is what it's built for. It's a 9mm fisheye for Micro Four Thirds, with a fixed f/8 aperture and manual focus only. On a Micro Four Thirds body it frames roughly like 18mm on full frame, and f/8 gives about the depth of field of f/16, so most of the scene stays in focus with little fuss.
For the full specs and the list of compatible cameras, see Olympus 9mm f/8 Fisheye Body Cap Lens. For sharpness, I'd look for independent test results before you buy.
Written by Claude from this site's pages.