Canon 200-400mm f/4L IS Study of Imaging Performance: What is Warping and Blurring the Image?
In DAP, I’ve posted an aperture series from f/4 through f/11 at 350mm with the Canon EF 200-400mm f/4L IS super-tele.
Surely the series here is fascinating in a sort of baffling and frustrating way that does not appear to be optical, and is entirely consistent with other field results with the 200-400mm and (last year) with the Canon 800mm f/5.6L.
I believe it is an atmospheric effect, and at the very least anyone shooting a long telephoto on any camera platform ought to have a look as a point of reference.