Ok, this is a kind of unique concept, that’s quite closer to older wet-plate camera lenses than to the modern conception.
Entaniya made the 250 (yes 250 degrees fisheye lens) into a lens system.
Given the front group is the same for everyone, and the 250 degrees of FOV is kept, by changing the mount and the rear group you change the coverage circle (and so, following, the focal length) in order to adapt to your cine camera mount and sensor size. Given the investment one of these lens represents, it’s a very interesting solution.
Here is the reference page of this incredible piece of engineering
All images are from Entaniya website.