this is a great fisheye lens for canon with declicked aperture and focus gear for use with follow focus

from B&H website:
The Canon EF mount Rokinon 8mm T3.8 Cine UMC Fisheye CS II Lens was developed primarily for film and video applications. The cine version of Rokinon's 8mm lens features industry-standard gearing for the focus and aperture ring, and the aperture ring has been de-clicked for smooth iris pulls. The aperture and focus scales have also been relocated to the side of the lens, where it is easier for focus pullers to read them.

This lens is compatible with APS-C-sized sensors and provides a 35mm-equivalent focal length of 12.8mm. Its 180° angle of view makes it well-suited to creative applications. The optical construction incorporates one hybrid aspherical element to reduce chromatic aberration and distortion to produce sharper imagery. Additionally, a UMC coating has been applied to lens elements to minimize lens flare and ghosting for more contrast-rich images.

180° fisheye lens is ideally suited for creative applications.
One hybrid aspherical element reduces chromatic aberrations and distortions in order to produce sharper images.
UMC coating improves light transmission and suppresses lens flare and ghosting for more contrast-rich, color-neutral images.
Geared aperture and focus rings are compatible with standard follow focuses for greater control over adjustment.
De-clicked aperture ring facilitates smooth, quiet exposure adjustments during recording.
A removable petal-type lens hood is included to help minimize flare by deflecting stray light from entering the lens.