It is an MD II lens, but no "MD" on bevel/name plate. And
it does not have MC lug nor the largest F-number is green.
$700 @2014

Rather large lens, focusing block moves toward the mount
when you set softness from 0(zero softness) to 1, 2, and 3,
the focus slightly shifts at the same time (a bit nuisance),
yes of course focus shift is a result of spherical aberration.