[Brightcolours]

Oh how ironic the world can be, while we're talking about large aperture F mounts.

 

Lenstips review of the Mitakon 85mm F1.2 in the Nikon mount... the Mitakon's vigneting..I quote:

 

"Employing the maximum relative aperture you have to take into account the loss of 45% of light (−1.73 EV) in the frame corners. It is not a low value but still the Mitakon is better than the Canon which lost as much as 51% of light. By f/1.4 the vignetting decreases to 40% (−1.49 EV). Once again that value is quite high but you should remember that the huge Otus by f/1.4 lost as much as 56% of light!" 

 

  Out bayoneted the Nikon F mount?  No........ how's that for a rabbit out of the hat-trick?

I think you are not taking into account lens design? The Canon lens is a very old design, going back to the end of the 1970's. That the current Canon with basically the same design, just a bit bigger back element, vignets a lot, it still vignets  less than the smaller mount diameter Canon FD relatives. There is more than one variable in vignetting.

The 55mm f1.2 lenses I have (you have) also a lot.

 

So yes, the 105mm f1.4 Nikkor vignets a lot due to the narrow mount's design limits. The Samyang 85mm f1.2 Vignets less than the Mitakon due to the wider mount diameter.