Aglet: I would struggle if I did not use that lens... I find that it has a very useful focal length range..
But yeah the bokeh going by what we see here does seem weird. It is almost as if the camera was rotating on its axis as the shutter was pressed.
I hear ya. I'd love it if I could just use this lens and not be concerned about ugly bokeh showing up.
but it does, so be aware of the weaknesses of whatever gear you're using.
Just because it cost a lot and came with an "L" in the moniker does not mean it's perfect.
It's a lens with compromises, as most are, unfortunately.
My new Nikon 70-200 f/4 VR shows some of the same effect. I knew this before I bought it as I could see the radial blur effect in a sample image someone posted from an early production sample. The shot was of grass, at a shallow angle, so you could see the blur quality around the central focus area. In the full size shot it was hard to notice the radial blur but in the small thumbnail size image it was grossly obvious.
What I've seen from modern zooms is more of this radial
bokeh tendency. I'm no lens designer but I think this is the price we pay for zooms that are super sharp with well controlled CA. Subjects in the focus zone are rendered very accurately but those just in front and behind get some strange distortion that seems to be caused by the special elements which are used to provide the corrections that give the focused area its sharpness and color convergence.
For anyone shopping for zooms tho, you can see this effect in the viewfinder if you can aim at some suitable subject matter tho. I find that tree branches in backgrounds, especially those where you also have plenty of sky available for contrast between them, will often show this distorted bokeh. Just focus the lens in front of or behind the branches and play with focal length, focus position and aperture and you'll see the distortions show up as you make the changes. On my 70-200/2.8 v2 I noticed entire sections of blurred branch actually disappearing at some settings! Very strange!
In general, I'm finding these radial bokeh effects show up more at close focus distances and at wide aperture settings. They often diminish in effect when stopping down.
Your mileage may vary.
This is just another instance of where you need to be wary when everyone raves about how good some piece of gear is. There's often a catch that's not been discussed as well. Forums like this are good education opportunities.
Knowing this I've kept a lot of lower quality lenses on hand for just this reason. Altho a cheap lens will rarely provide the biting sharpness of the pro glass, they'll also rarely show these same distracting aberrations. They'll have their own problems of course. But a $200 lens may provide you a workable option when the $2000 one fails in this way. Some of my best images were made with second-hand consumer grade lenses merely because they provide a balanced "look" with adequate sharpness and smooth bokeh. I wouldn't expect these cheap lenses to perform well at a race-track though, they focus too slowly.