Canon classifies the Canon EF 400mm f/5.6 L USM Lens as a "Super Telephoto" lens. It issuper in image and build quality, but is not super in size.
The Canon EF 400mm f/5.6 L USM Lens is relatively light in weight but very solidly built
The 400 f/5.6 L internally focuses very fast and quietly thanks in part to a Ring USM (Ultrasonic Motor). FTM (Full Time Manual) focusing is featured and attached filters do not rotate.
CA (Chromatic Aberration) is very well controlled. Color, saturation and contrast are excellent. Bokeh (background blur quality) is very nice thanks in part to an 8-blade aperture. Vignetting is very well controlled. Very minor pincushion distortion is present, but it will not be noticed in most (if any) of your images.
The Canon EF 400mm f/5.6 L USM Lens performs superbly in the sharpness department. Even wide open, the 400 f/5.6 produces very sharp images right into full frame corners.