What is the difference between the Mark I and Mark II fisheye lenses?
The MKI fisheye was designed for cameras such as the Sony VX1000 Mini DV camera. Many professional users objected to the amount of vignetting present in the MKI Ultra Fisheye. The MKII fisheye was designed for newer cameras such as Sony VX2000/PD150 and the Canon GL1/2, which have larger lenses, requiring a larger fisheye. Vignetting was eliminated in the Mark II design.