The Canon EF 70-200mm f/2.8L IS II has an image quality problem under certain conditions that include focal length and distance and apertures.
It’s a really odd problem because image quality goes from very good at f/2.8 to outstanding at f/4 to slightly degraded at f/5.6 to strongly degraded at f/8 and even worse at f/11.
I’ve never seen anything like it before, and it’s in the worst possible place: smack dab in the center! The issue shows itself clearly (blurrily?) at 200mm, but I suspect that it extends well down into the focal length range, based on the results at 135mm.
I’m exploring this issue further, but it’s a darn shame, because at f/4 the 70-200mm f/2.8L IS II can be outstanding.