yup, double lines.

stopping down unavoidably reduces spherical aberration. if the lens is overcorrected for spherical aberration, stopping down will therefore improve the bokeh behind the plane of focus. it won't be quite as blurry, and the aperture blades become a factor, but it's something to keep in mind.

a lens with undercorrected spherical aberration will have smooth bokeh behind the focal plane, either wide open or stopped down, especially if the aperture blades form a more perfect circle.

i wish lens designers would just say whether a lens is overcorrected or undercorrected for spherical aberration. that would make things a lot easier!