We continuously see new patents for diffractive optics lenses, something Canon continues to work and that we’ll see in a new EF 600mm f/4 DO IS sometime in the future (Photokina 2018 perhaps?).
This latest patent selectively uses aluminum to reduce light scattering or flare in diffractive lens elements. Keith at Northlight Images, who is Read more. . . . canonrumors.com