Newbie bokeh question - picture included

[tvtt]

another question - does the distance from the object in focus to the background make a difference in bokeh? For example, could my swirly be due to varying distances of the background from the focus?

It could be, and the oddities caused by the lens could be lessened by using a smooth background, but your best option really is just to stop down a little. Things further away from the focal plane will create larger and larger circles of confusion, which take the shape of the aperture; hence why for higher quality bokeh, more blades in the aperture (thus making it closer to a circle in shape) is a must. It also has partly to do with how well the blades are aligned in the first place so that they stay in roughly the shape of a circle.

Unfortunately with uneven rendering of bokeh like this, if you were to say, hold a stick near the dogs head about half a foot behind, the brown contrast against the green which is much farther away from the focal plane would indeed be harsh and not as, well, silky and creamy are probably the best words for it.

thanks, that helps a lot!