Quote Originally Posted by AtlantaTerry View Post
Polyglot, I am familiar with the term "bokeh" but never heard of "nisen-bokeh". What is that?
It simply means harsh or distracting bokeh, often characterised with a double line effect with straight edges that are out of focus, or a kind of onion ring or doughnut effect in out of focus highlights. For example (Edit, the effects below where created artificially but they illustrate the point):

vs
or
vs

It's worth noting however that the same lens will often have a very harsh bokeh one side of the plane of focus and quite smooth on the opposite side. Some lenses are smooth on both sides.