I agree with James that you need a shade.
But these days it is not so essential. This is because unlike on film - most fisheye shots are taken with the sun, rather than against it (Rand, I added the "most" for your benefit, there).
Om film photographers would almost always try an include the sun in their fisheye shots. This would mean a shade to protect against flare from the dome and lens was essential. These days we shoot away from the sun and it is less essential. Just a thought.
Alex
Here is a shot of mine take with the 10.5 on digital.

While here is an example from Linda Dunk's 1996 winning BSoUP portfolio. Taken on film - note the sun:
