ePHOTOzine has completed their review of the brand new Canon EF 400mm f/4 DO IS II and have come away quite impressed. The original 400 DO was one of my favourite Canon lenses and I will definitely be replacing it with this lens.
“As you might expect from a lens that commands such a high price, this lens performs superbly as far as sharpness is concerned. Diffraction appears to be the ceiling for performance, with this lens delivering outstanding sharpness across the frame at maximum aperture. Although sharpness in the centre of the frame peaks at f/5.6, on the whole, performance is reduced gradually as the aperture is stopped down. It would be a big ask for Canon to defeat physics to improve performance in this respect. Sharpness remains excellent across the frame, until the aperture is stopped down beyond f/11.”