The crop factor you are showing for the BMPCC camera are more than a bit misleading since I don't recall ever seeing a 24mm FISHEYE lens. This needs to be approached from the standpoint of angle of view. A 15mm fisheye on a full frame Fisheye lens is 180 degrees, a 15mm rectilinear lens on full frame is 110 degrees.
The Samyang 8mm has an AOV of 180 degrees on the Nikon APS-C 1.5X sensor and an AOV of 167 degrees on the Canon 1.6X APS-C sensor so with this lens you need to do the crop from the APS-C size not the full frame size, it would be a circular fisheye on full frame like the Canon 8-15 fisheye zoom.
The Panasonic 8mm fisheye M43 lens has an AOV of 180 degrees on the M43 size sensor, these lenses have about a 1.3X crop on the BMPCC so you would be going from an AOV of 180 degrees to an AOV of around 135 degrees for the Panasonic 8mm, still quite fishy.
The Panasonic 7-14 rectilinear zoom M43 lens has an AOV of 114-75 would would come out at around 87-57, give or take a few degrees.
If you just take your 8mm full frame circular image and divide by 3 you don't really get a true picture of the final AOV of the lens. That would make the 180 degree fisheye a 60 degree fisheye, a 24mm rectilinear lens is 84 degrees so not even close. You would have to think in terms of a 60mm fisheye and I don't know how you do that. If you take the difference between the 15 Fisheye and 15 rectilinear and divide 180 degrees by 110 degrees you get 1.636 times the 60mm fisheye would make the AOV about a 98 degree fisheye also no where near the 84 degrees of a 24mm.
Edited by Phil Rudin, 17 August 2013 - 09:23 AM.