d12e8b4e_sic_Dome_projection___Domerama__Spherical_mirror
[0] Convenience [Fisheye] There are no actual universal fitting. You often need to find the correct lens to a specific projector. [Spherical mirror] 
One is not limited to particular projectors for which fisheye lens can be fitted. Existing projectors can be used or a projector chosen for particular attributes such as brightness, resolution, or contrast.
Geodesic Dome projection » Domerama
Spherical mirror