Robert - thanks. These were all taken wide open, so f/2 for the 135mm. Closing down, even to f/2.8, makes the disk edges non-circular. The 135 DC is a favorite lens. Still fairly expensive second-hand, though prices came down quite a bit after release of the 105mm f/1.4.
Erik and Charlie, thanks, that's good news - something I can get at to clean. I'd wondered if I was seeing diffraction around something internal, with the lens so far out of focus. I did try to clean the rear element with a blower, but probably left a few specks that I'll need to take off with a cloth.
Cheers again, John