Nikon PC NIKKOR 35mm f-2.8 - Manual (Page 18)

Maximum Permissible Shift
Depending on the direction of shift, however, there is
a maximum permissible shift, beyond which distortion
and/or vignetting may occur in the picture corners,
because the film format is rectangular while image area
produced by the lens is circular. The amount of maxi­
mum permissible shift (7, 8 or 11) is indicated in
millimeters at each click-stop on the lens barrel. The
diagrams at right show the limits based on the direc­
tion of shift.
Note: When you use a Nikon polarizing filter in combination
with a lens hood, vignetting will occur even at the maximum
permissible amount of shift at each click-stop.