I played around with the circular end of the 8-15mm fisheye on a few dives in Komodo. It is kind of fun. I thought motion made it more interesting. The distortion and view of the reef is interesting as well. It certainly isn't something you would film with on a regular basis. Unless you had a specific idea you were going for. I am curious to know if there is a way to make the circle not cut off on the top and bottom.
Anyway, let me know what you think.