8mm is a circular fisheye - on FX, you'll get a a completely circular image in the middle, and everything is black beyond that. it is quite interesting, and a fun lens to play with. You can use it on DX as well, and you'll get a little more coverage, but you lose the complete circle (top and bottom chopped off).
the 10.5DX I believe is a rectangular fisheye, so it has the fisheye distortion, but the image stretch from corner to corner, filling the frame.
I have the 8mm, and it's fun. But thinking about adding a rectangular fisheye for my bag in the sorta distant future (I heard the Sigma 15mm is quite good). Too many toys, too little money... (of course, I want the 200-400 as well) *sigh
Chestnut wrote:
the 10.5DX I believe is a rectangular fisheye, so it has the fisheye distortion, but the image stretch from corner to corner, filling the frame.
No such thing as a rectangular fisheye. (Well, maybe some anamorphic cinema lens). The image that all non-anamorphic lenses project is round. The shape of the sensor is what makes the image rectangular. If you trim the built in hood on the 10.5 DX and use it on an FX camera, you get a round image.
